Energy Usage During Exercise: How It Affects Your Workouts

By Jessica Smith, Fitness Consultant


While most people know that aerobic exercise is good for the heart and that resistance training helps build lean body mass, most people don’t fully understand how these different types of exercise elicit very different responses within our bodies. A basic understanding of how our body uses energy during different forms of exercise is critical for designing an effective exercise program. We will focus on energy systems—i.e., how the body utilizes fat, carbohydrate, and protein to produce energy—and how these energy systems are relied upon during different forms of exercise.

This article will give you a better understanding of how your body converts the food you eat into usable energy and how targeting specific energy systems will help you achieve your personal health and fitness goals.

Energy Systems Review

In general, there are three basic energy systems: (1) the phosphagen system (also referred to as the immediate energy system), (2) the glycolytic energy system (also referred to as the nonoxidative or anaerobic system), and (3) mitochondrial respiration (also referred to as the oxidative or aerobic system).

Regardless of what energy system is used, the end result is the production of adenosine triphosphate (or ATP). ATP is extracted from the food we eat (fat, carbohydrate, and protein) and is required for the biochemical reactions involved in any muscle contraction. The intensity and duration of the activity dictates which foodstuffs are broken down as well as which energy system predominates. It is important to keep in mind, however, that no energy system acts alone.

The relative contribution from each system depends on the intensity and duration of the activity. The Phosphagen or Immediate Energy System The phosphagen system is active during all-out exercise that lasts about 5 to 10 seconds such as a 100-meter dash, diving, jumping, lifting a heavy weight, dashing up a flight of stairs, or any other activity that involves a maximal, short burst of power. This system relies on stored ATP and to a larger extent, creatine phosphate to provide immediate energy. For any maximal intensity exercise lasting longer than 10 seconds, assistance from other sources of energy is required.

Glycolytic Energy or Anaerobic System The glycolytic energy system (also called glycolysis) involves the partial break down of glucose to a molecule called pyruvate. During this process, a relatively small amount of energy is produced. When oxygen demands exceed the oxygen supply, pyruvate is converted to lactate. Under these circumstances, glycolysis is often referred to as “fast” or “anaerobic” glycolysis. Anaerobic glycolysis is a key contributor to the total energy requirements for moderate to high intensity exercise lasting about one to two minutes. Although this system can provide a rapid source of energy, it is only about half as fast as the phosphagen system.

When there is enough oxygen to meet the oxygen demands of the activity, such as during prolonged light to moderate intensity exercise, glycolysis proceeds much slower and the pyruvate that is formed participates in the formation of additional energy via aerobic processes (see Aerobic System discussion below). In this case, glycolysis is sometimes referred to as “aerobic” or “slow” glycolysis.

We often think of low to moderate intensity aerobic exercise as a good way to burn a significant amount of fat. While this is true, aerobic energy can be derived from carbohydrates and to a much smaller extent, protein. In fact, most people don’t realize that even during light to moderate exercise, carbohydrates can provide up to 40 to 60 percent of the total energy requirements. (See Table 1.) In contrast, protein is not a preferred source of energy during any form of exercise (assuming an adequate diet) and generally contributes less than 10 percent of the total energy requirements.

Monitoring Your Energy Usage

One of the most effective methods of determining the predominant energy system during a specific form of exercise is by monitoring your heart rate. Heart rate monitoring can help you determine the intensity of your workout as well as estimate the heart rate at which you transition from aerobic to anaerobic exercise (i.e., from carbohydrate and fat usage to predominantly carbohydrate).

While the transition point differs from person to person, you can get a general idea of where you transition from aerobic to anaerobic exercise by watching for substantial increases in heart rate, muscle fatigue, or in breathing depth and frequency. If you are truly engaging in anaerobic exercise, you will not be able to sustain the intensity of the exercise for longer than about one to two minutes.

If you notice your intensity dropping off, you were probably performing anaerobic exercise. In contrast, if you are able to sustain your exercise intensity longer than about two minutes, you are probably exercising aerobically. As your fitness improves, you will be able to perform higher intensity exercise for longer periods of time.

Exercise Mode and Energy Usage

Keep in mind that although resistance training doesn’t necessarily burn a significant number of calories, it can provide significant health and fitness benefits. Not only does resistance training increase lean body mass (i.e., muscle), which burns more calories than fat even while at rest, engaging in a regular resistance training can have positive effects on elements such as cholesterol, glucose metabolism, and bone density, to name a few.

Circuit Training Circuit training is sometimes considered a type of resistance training, but it is actually a compromise between resistance training and cardiovascular training. Essentially, circuit training can improve muscle endurance as well as provide modest gains in aerobic capacity. Because it is generally a low to moderate intensity workout that is sustained for an hour or more, circuit training is primarily an aerobic activity.

Aerobic Exercise: Walking, Jogging, Traditional Hi-Lo Aerobics, and Step Aerobics “Aerobic” exercise is typically touted as a great way to burn a lot of fat. While this is not necessarily incorrect, it can be misleading. For example, at about 25 percent of aerobic capacity (i.e., low intensity exercise), fat is the primary source of fuel, but you are not burning a significant number of calories. If your goal is to lose weight, the key consideration is the net deficit in calories, not where the calories come from. As exercise intensity increases, the number of calories burned also increases. Therefore, while it is true that fat contributes a greater percentage of the total energy during lower intensity exercise, at higher intensity exercise, the total quantity of fat utilized may be greater for exercise performed for an equivalent period of time.

So How Does Energy Usage Affect Your Workout?

If you don’t have a specific goal in mind, but simply want to improve your overall health, the American College of Sports Medicine recommends moderate intensity physical activity performed for at least 20 to 30 minutes, excluding time spent warming up and cooling down, 3 to 5 times a week. If, on the other hand, you are training for some type of competitive event, make sure that your training program emphasizes the type of activity involved in that event.

For example, if you are training for a triathlon, engaging in a power lifting training program three days a week will not make the best use of your time. You need to actively engage in running, biking, and swimming. Finally, if your goal is to lose weight, caloric deficit is key. You should aim for a caloric deficit of about 500 calories a day through decreased energy intake, increased energy expenditure, or a combination of the two. Although there are numerous types of exercise that are effective for weight loss, a combination of regular aerobic exercise and resistance training is a good place to start.

Table 1. Nutrient usage at different exercise intensities

About Jessica Smith

Jessica Smith Jessica Smith, Fitness Consultant. Jessica has a Master’s degree in Bioengineering with an emphasis in biomechanics. She presently has her own consulting business and provides expertise in the areas of health and fitness, exercise physiology, and biomechanics, among others. Jessica has been involved in a number of projects including the development of health and fitness related website content, fitness equipment design, and program development for group exercise classes. She has also authored several articles for fitness magazines. Jessica was a member of the 1990 NCAA championship gymnastics team and is now an avid recreational athlete. She currently holds certifications through the Aerobics and Fitness Association of America and the American College of Sports Medicine.

Understanding Energy Systems: ATP-PC, Glycolytic and Oxidative – Oh My!

Human bioenergetics is an interesting topic. However, energy systems function is understood by few and/or can be confusing to many. Open a quality exercise physiology text and it can leave you saying “huh?” when reading about aerobic, anaerobic, and immediate energy metabolism. It can get even worse when sifting through all the biochemical processes.

Is it important to be able to explain the chemical breakdown of the oxidative Krebs cycle or anaerobic glycolysis if you’re a coach or an athlete in training? Not really. However, knowing the basics of how we generate energy can be helpful in understanding how we fatigue and what training measures can be used to minimize it. Let’s get going as simply as possible. I will do my best, but some “high-tech” discussion is necessary.

The first thing to remember is that ANY muscle contraction/force exertion is due to a molecule called adenosine triphosphate (ATP). When an ATP molecule is combined with water the last of three phosphate groups splits apart and produces energy. This breakdown of ATP for muscle contraction results in adenosine diphosphate (ADP). The limited stores of ATP must be replenished for work to continue; so chemical reactions add a phosphate group back to ADP to make ATP.

How ATP Is Produced

Take three different activities and put them on a continuum. On one end would be a quick, explosive burst such as throwing a punch. On the other end would be an extended, lower-level event such as walking five miles. Between the two could be anything: an intense twenty-second activity, one minute of constant force exertion, or a five-minute event with varied intensities of effort.

As you can see, there are many expressions of energy output depending on the amount of force required and the length of the activity. What then, is the energy source for activities that fall on the continuum at various points? This is the essence of bioenergetics – so many possibilities and so many factors involved.

The Three Energy Systems

Conventionally, there are three energy systems that produce ATP: ATP-PC (high power, short duration), glycolytic (moderate power/short duration), and oxidative (low power/long duration). All are available and “turn on” at the outset of any activity. What dictates which one (or two) is relied upon the most is the effort required.

Take home point: ATP must be present for muscles to contract. It can be produced via the ATP-PC system, the glycolytic system, or the oxidative system. If depleted, it must be replenished if further muscle contraction is to continue.

Perform an explosive, one-time movement such as a standing long jump or vertical jump and you exert maximal effort, but guess what? You will not become fatigued from this single exertion. However, jump multiple times and eventually you will become fatigued. Going all-out for as long as possible will deplete immediate ATP stores, then glycolytic stores. Continuing effort must be fueled by the oxidative system at a lower intensity, all other factors being equal. The most pure aerobic activity that exists is sleeping or lying comatose.

The ATP-PC Energy System – High Power/Short Duration

ATP and phosphocreatine (PC) compose the ATP-PC system, also sometimes called the Phosphogen system. It is immediate and functions without oxygen. It allows for up to approximately 12 seconds (+ or -) of maximum effort. During the first few seconds of any activity, stored ATP supplies the energy. For a few more seconds beyond that, PC cushions the decline of ATP until there is a shift to another energy system.It is estimated the ATP-PC system can create energy at approximately 36 calories minute.

Examples: a short sprint, lifting a heavy resistance for three repetitions, or pitching a baseball.

The Glycolytic System – Moderate Power/Moderate Duration

Now it becomes more complicated as energy demands shift to this system. The glycolytic system is the “next in line” tool after the ATP-PC system runs its course. Dietary carbohydrates supply glucose that circulates in the blood or is stored as glycogen in the muscles and the liver. Blood glucose and/or or stored glycogen is broken down to create ATP through the process of glycolysis. Like the ATP-PC system, oxygen is not required for the actual process of glycolysis (but it does play a role with the byproduct of glycolysis: pyruvic acid). It is estimated glycolysis can create energy at approximately 16 calories per minute.

Here is where it gets interesting. After maximum power declines around 12 seconds, further intense activity up to approximately 30 seconds results in lactic acid accumulation, a decrease in power, and consequent muscle fatigue. This high, extended effort is labeled “fast” glycolysis. Exerting further effort up to approximately 50 seconds results in another drop in power due to the shift in dependence on the oxidative system. Bottom line: it is getting tougher.

Example: think of an all-out sprint, to a slower jog, to an eventual walk. That is the progression of the three energy systems when going all-out.

Enter “slow” glycolysis into the discussion (warning: more science jargon ahead, but hang in there). Recall the byproduct of glycolysis is pyruvic acid. In fast glycolysis, more power can be generated, but pyruvic acid is converted to lactic acid and fatigue ensues quickly. Slow glycolysis is different. Relatively less power is generated, but pyruvic acid is converted to acetyl coenzyme A (acA), fed through the oxidative Krebs cycle, more ATP is produced, and fatigued is delayed. Thus, extreme fatigue can be avoided (but relatively less-intense effort can continue to be expressed) in slow glycolysis as compared to fast glycolysis.

Examples: any moderately-long runs such as 200-400 yards, a 1:30 effort of all-out MMA maneuvers, or a one-minute full-court press – offense display – and another full-court press effort in basketball.

The Oxidative System – Low Power/Long Duration

Your maximal effort was fueled initially by the ATP-PC, but your performance declines. Continued effort results in further decline, either via fast glycolysis (quick decline) or slow glycolysis (slower decline). You’re now entering the complex world of the low power but longer duration oxidative system, which is estimated to create approximately 10 calories per minute.

Examples: 6-mile run, low-level manual labor on an eight-hour work shift, or a 3-mile walk.

The effort demand is low, but ATP in this system can be produced three ways:

  1. Krebs cycle
  2. Electron Transport Chain
  3. Beta Oxidation.

Let me explain the science, and then I’ll get back to you in plain English. The Krebs cycle is a sequence of chemical reactions that continues to oxidize the glucose that was initiated during glycolysis. Remember the acA? It enters the Krebs cycle, is broken down in to carbon dioxide and hydrogen, and “poof” two more ATP molecules are formed.

Here is the problem: the hydrogen produced in the Kreb’s cycle and during glycolysis causes the muscle to become too acidic if not tended to. To alleviate this, hydrogen combines with the enzymes NAD and FAD and is sent to the electron transport chain. Through more chemical reactions in the electron transport chain, hydrogen combines with oxygen, water is produced, and acidity is prevented. Notice this takes time due to the need of oxygen, which is why the oxidative energy takes a while and intensity of effort declines (i.e., all-out sprinting becomes slow jogging/walking).

The Krebs cycle and the electron transport chain metabolize triglycerides (stored fat) and carbohydrates to produce ATP. The breakdown of triglycerides is called lipolysis. The byproducts of lipolysis are glycerol and free fatty acids. However, before free fatty acids can enter the Krebs cycle they must enter the process of beta oxidation where a series of chemical reactions downgrades them to acA and hydrogen. The acA now enters the Krebs cycle and fat is metabolized just like carbohydrates.

In Plain English

Due to the time-line, the oxidative system provides energy much more slowly than the other two systems, but has an almost unlimited supply (in your adipose sites – yeah, that stuff you can pinch!). The oxidative system by itself is used primarily during complete rest and low-intensity activity. It can produce ATP through either fat (fatty acids) or carbohydrate (glucose).

Because fatty acids take more time to breakdown than glucose, more oxygen is needed for complete combustion. If efforts are intense and the cardiovascular system cannot supply oxygen quickly enough, carbohydrate must produce ATP. However, in very long duration activities (i.e., marathons), carbohydrates can become depleted and the body looks to fat as the energy producer.

A Few Words on Protein

In extended activities protein can be used as a “last resort” for energy production (in rare cases where carbohydrates are depleted and stored fat is minimal). In such cases, it can supply as much as 18% of total energy requirements. The building blocks of protein – amino acids – can be either converted into glucose (via gluconeogenisis) or other sources used in the Krebs cycle, such as acA. But understand protein cannot supply energy at the same rate as carbohydrates and fats, thus it’s basically a non-issue).

Programming for the Energy Systems

It is estimated that the ATP-PC and glycolytic systems can be improved up to 20% and the oxidative system by a whopping 50% (but in untrained subjects only). Regardless, sport-specific conditioning plans and optimal nutritional intake need to be implemented. But be aware of the reality of genetics: your unalterable muscle fiber composition plays a huge role. If you possess predominately slow type I fibers (endurance) or fast type II fibers (strength), you can only do so much. For me, this explains why I never got a sniff of any national-level competitions back in the early 1980s.

Photos courtesy of .


The fuels used in anaerobic exercises—sprinting, for example—differ from those used in aerobic exercises—such as distance running. The selection of fuels during these different forms of exercise illustrates many important facets of energy transduction and metabolic integration. ATP directly powers myosin, the protein immediately responsible for converting chemical energy into movement (Chapter 34). However, the amount of ATP in muscle is small. Hence, the power output and, in turn, the velocity of running depend on the rate of ATP production from other fuels. As shown in Table 30.3, creatine phosphate (phosphocreatine) can swiftly transfer its high-potential phosphoryl group to ADP to generate ATP (Section 14.1.5). However, the amount of creatine phosphate, like that of ATP itself, is limited. Creatine phosphate and ATP can power intense muscle contraction for 5 to 6 s. Maximum speed in a sprint can thus be maintained for only 5 to 6 s (see Figure 14.7). Thus, the winner in a 100-meter sprint is the runner who slows down the least.

Table 30.3

Fuel sources for muscle contraction.

A 100-meter sprint is powered by stored ATP, creatine phosphate, and anaerobic glycolysis of muscle glycogen. The conversion of muscle glycogen into lactate can generate a good deal more ATP, but the rate is slower than that of phosphoryl-group transfer from creatine phosphate. During a ~10-second sprint, the ATP level in muscle drops from 5.2 to 3.7 mM, and that of creatine phosphate decreases from 9.1 to 2.6 mM. The essential role of anaerobic glycolysis is manifested in the elevation of the blood-lactate level from 1.6 to 8.3 mM. The release of H+ from the intensely active muscle concomitantly lowers the blood pH from 7.42 to 7.24. This pace cannot be sustained in a 1000-meter run (~132 s) for two reasons. First, creatine phosphate is consumed within a few seconds. Second, the lactate produced would cause acidosis. Thus, alternative fuel sources are needed.

The complete oxidation of muscle glycogen to CO2 substantially increases the energy yield, but this aerobic process is a good deal slower than anaerobic glycolysis. However, as the distance of a run increases, aerobic respiration, or oxidative phosphorylation, becomes increasingly important. For instance, part of the ATP consumed in a 1000-meter run must come from oxidative phosphorylation. Because ATP is produced more slowly by oxidative phosphorylation than by glycolysis (see Table 30.3), the pace is necessarily slower than in a 100-meter sprint. The championship velocity for the 1000-meter run is about 7.6 m/s, compared with approximately 10.2 m/s for the 100-meter event (Figure 30.19).

Figure 30.19

Dependence of the Velocity of Running on the Duration of the Race. The values shown are world track records .

The running of a marathon (26 miles 385 yards, or 42,200 meters), requires a different selection of fuels and is characterized by cooperation between muscle, liver, and adipose tissue. Liver glycogen complements muscle glycogen as an energy store that can be tapped. However, the total body glycogen stores (103 mol of ATP at best) are insufficient to provide the 150 mol of ATP needed for this grueling ~2-hour event. Much larger quantities of ATP can be obtained by the oxidation of fatty acids derived from the breakdown of fat in adipose tissue, but the maximal rate of ATP generation is slower yet than that of glycogen oxidation and is more than tenfold slower than that with creatine phosphate. Thus, ATP is generated much more slowly from high-capacity stores than from limited ones, accounting for the different velocities of anaerobic and aerobic events.

ATP generation from fatty acids is essential for distance running. However, a marathon would take about 6 hours to run if all the ATP came from fatty acid oxidation, because it is much slower than glycogen oxidation. Elite runners consume about equal amounts of glycogen and fatty acids during a marathon to achieve a mean velocity of 5.5 m/s, about half that of a 100-meter sprint. How is an optimal mix of these fuels achieved? A low blood-sugar level leads to a high glucagon/insulin ratio, which in turn mobilizes fatty acids from adipose tissue. Fatty acids readily enter muscle, where they are degraded by β oxidation to acetyl CoA and then to CO2. The elevated acetyl CoA level decreases the activity of the pyruvate dehydrogenase complex to block the conversion of pyruvate into acetyl CoA. Hence, fatty acid oxidation decreases the funneling of sugar into the citric acid cycle and oxidative phosphorylation. Glucose is spared so that just enough remains available at the end of the marathon. The simultaneous use of both fuels gives a higher mean velocity than would be attained if glycogen were totally consumed before the start of fatty acid oxidation.

A List of 14 Types of Cardio Exercises to Get You Moving

When most people think of cardiovascular (cardio) exercises, the first activities that come to mind are running, cycling, or swimming.

Yes, these are great ways to get your heart rate up, but not everyone enjoys them. Cardio should be a key part of your healthy lifestyle. Luckily, there’s no “one-size-fits-all” approach.

If you’re looking to incorporate more cardio into your exercise routine, don’t be intimidated by the seasoned marathon runners you see around your neighborhood. Heart-healthy workouts don’t have to involve spending hours on the treadmill. There are plenty of fun and creative ways to get your cardio in and actually enjoy it.

Why Do You Need Cardio in the First Place?

Cardio is defined as any type of exercise that gets your heart rate up and keeps it up for a prolonged period of time. Your respiratory system will start working harder as you begin to breathe faster and more deeply. Your blood vessels will expand to bring more oxygen to your muscles, and your body will release natural painkillers (endorphins).

The physical and mental benefits of this type of exercise are seemingly endless.

  • Manage your weight: The Centers for Disease Control and Prevention (CDC) say there’s extensive scientific evidence that 150 minutes of moderate-intensity cardio per week will help you maintain your weight over time.
  • Ward off heart disease: Research has shown that getting your heart rate up with regular cardio exercises can help prevent cardiovascular disease, which accounted for 31 percent of global deaths in 2012.
  • Mood improvement: It’s probably no surprise to you, but research supports the role that cardio exercise plays in improving your mood and increasing your happiness. Cardio ups the production of those feel-good painkillers called endorphins.
  • Live longer: The Mayo Clinic suggests that people who regularly perform cardio exercise will live longer./li>

Your Cardio Exercise Options

Think outside the box and try something new with these fun cardio options. The key to sticking with any successful workout plan is discovering an activity that you enjoy.

Once you find an exercise you love, you’ll be having so much fun that you’ll have to be reminded that you’re improving your health, too!

1. Jump Rope

Chances are, you haven’t jumped rope since 4th grade recess. If that’s the case, go get yourself a jump rope today! This form of cardio can be done just about anywhere. Turn up your favorite playlist and jump to the beat. Tossing your jump rope in a backpack, suitcase, or purse will help you squeeze in your 150 minutes of exercise per week whenever you have some spare time.

2. Dancing

Whether or not you think you have two left feet, dancing is a great way to blow off some steam while also getting your cardio in. You may think that dancing’s limited to Zumba classes, but what’s keeping you from simply dancing around your room? Crank the tunes and dance yourself silly.

3. Organized Sports

You may not think of yourself as a “sports person,” but there are tons of adult sports leagues out there that are full of people just like you — people who want to have fun and be healthy. Sign up for soccer, flag football, basketball, or whatever suits your fancy. Running around a field or court is guaranteed to increase your heart rate. Check your community for noncompetitive sports leagues. Maybe you’ll even make a new friend while you’re at it!

4. Power Walking

You don’t have to look like one of these power walkers to reap the benefits of this type of cardio. Step outside (or stick to the treadmill if the weather is bad) and pick up the pace.

5. Swimming

This low-impact form of cardio is a great way to get your heart rate up while protecting your joints. If you’re not fully confident in your swimming skills, grab a kickboard and do a few laps. This will engage not only your legs, but your abs, too.

6. Boxing

We can’t all be Rocky Balboa, but anyone can use boxing to get healthy. Just 30 minutes of boxing can help you burn up to 400 calories.

7. Trampoline-ing

If you have a huge, bouncy trampoline in your backyard, that’s awesome. Jumping and playing around is not only good for you, but fun, too!

If you don’t have a huge trampoline, don’t count yourself out of this one. You can get a compact trampoline to keep in your apartment. Putting on your favorite tunes and running or bouncing in place can be just as effective.

8. Cycling

There are plenty of ways to fit this type of cardio into your day. Swap your car for a bike on your next trip to the grocery store. Switch it up and ditch the treadmill for the stationary bike on your next trip to the gym. Bite the bullet and try that indoor cycling studio you’ve been eyeing for the past six months, or buy a trainer so you can ride your road bike in your house or garage.

9. Hiking

Love the outdoors? Hiking might be just the ticket to increase your ticker’s health. Getting moving outside will not only increase your cardiovascular fitness, but also boost your emotional well-being.

10. Rowing

Think that rowing machine is just for those who want bulging biceps? Think again! Squeezing rowing into your gym routine can give you an extra cardio boost, as well as strengthen your abs and back muscles. If you’ve never tried it, challenge yourself with something new.

11. Hula-Hooping

Sure, you probably haven’t done it since the last kids’ birthday party you went to, but why not? Swinging those hips around will up your heart rate and improve your core strength. And don’t worry — they make them in adult sizes.

12. Walking

You may be wondering if walking counts as cardiovascular exercise. Of course! This is a great starting place for people who are new to exercise. Even a 10-minute walk can get you on the road to improved heart health. Experienced exercisers benefit from it, too.

13. Jumping Jacks

If you haven’t done these since high school gym class, you’re missing out! This equipment-free activity can get your heart rate up in no time. Plus, they’re easy to do from anywhere. Start jumping first thing in the morning, when you need a break from your desk, or while you’re waiting for your dinner to finish cooking.

14. Stairs

Climbing stairs is a fantastic way to get your heart pumping and your body sweating. Find a park with a big set of stairs, or just a stairwell at a nearby building. Any climb will do. And if you need to stay indoors, the Stairmaster is your friend.

The Takeaway

There’s no debate that cardiovascular exercise is a key part of a long and healthy life. But that doesn’t mean it’s easy to make cardio a regular routine. Just remember that if you keep an open mind and get creative, there are plenty of ways to get your heart rate up. You shouldn’t feel confined to the treadmill.

The most important part of any fitness routine is finding what you enjoy. You’re much more likely to stick with a routine if it’s something you actually like. So experiment, try new things, and figure out how to relish breaking a sweat.

7 Types of Basic Cardio Workouts

Cardio workouts involve moderate to vigorous activity that uses large muscle groups to spike the heart rate to at least 65 percent of its maximum capacity. While this intensity isn’t the go-to for building muscle, but it can help you burn fat and lose weight with more benefits to boot:

“It increases the efficiency of the heart, and endurance of the muscles and heart,” explains Michele Olson, PhD, fellow at the American College of Sports Medicine (ACSM), and adjunct professor of sports science at Huntingdon College in Montgomery, AL. “It also reduces the risk of heart disease by making the heart a stronger muscle.”

RELATED: How Exercise Burns Fat

This improves the organ’s efficiency and stamina, according to Marius Maianu, ACSM certified exercise physiologist and fitness consultant at Cooper Clinic in Dallas.

So how much cardio do you need? Maianu recommends at least 20 minutes, but preferably 30 to 60 minutes, three to five times a week. While that can amount to quite a bit of time, there’s good news: Cardio workouts don’t have to be boring. Here are the different types of cardio workouts, their benefits, and why you might want to try them—especially if your goal is to achieve the fastest weight loss.

7 Basic Cardio Exercises

1. Circuit training

If running on a treadmill isn’t your thing, circuit training may be a good way to get in cardio. Safe for beginners and advanced gym-goers alike, “it’s all about moving from one exercise to another,” explains Olson. While you can stick with traditional cardio moves like jumping rope, box step-ups, and jumping jacks, a weight-training circuit that alternates between resistance-training moves like jumping jacks and dumbbell squats, skipping rope and push-ups, or step-ups and back rows can make your workout even more efficient: You’ll burn calories, reap benefits of cardio, and strengthen your muscles while you’re at it.

2. High-intensity interval training

Also known at HIIT, this technique calls for an all-out effort during quick bursts of exercise. Afterward, you rest for a short period of time, insuring you get the most out of every minute of your workout. Compared to other cardio techniques, “it’s more effective at reducing belly fat and has an after-burn effect, too,” Olsen says, describing the way the body burns calories after the activity in its effort to recover. The downside is that you really have to push yourself to about 90-percent of your max heart rate to truly be doing HIIT, he adds—meaning this approach isn’t for beginners.

RELATED: Beginners Guide to Interval Training

3. Kettlebell training

While you might think kettlebells (those round weights with handles) are a resistance-training tool, any exercise that involves swinging the bells can deliver a nice cardio benefit. “They’re designed to develop muscular endurance rather than pure strength and use the entire body, including the legs, core, back, shoulders, and hips,” Olson says. Don’t be fooled though—using them properly isn’t as simple as you might think since form is super important. If you’re new to kettlebells, learn how to correctly use them to avoid cardio injuries.

RELATED: Everyday Kettlebell Workout Routine

4. Non-impact workouts

Biking, rowing, and swimming can deliver the benefits of cardio and help with fat burn plus they can be adjusted to meet your fitness level and capabilities. “Rowing and swimming more actively engage the upper body and core, but all three are low impact so they can be beneficial for people with frail bones, such as individuals with osteoporosis or other orthopedic issues including back pain from a herniated disk,” Olson says.

RELATED: Beginners Guide to Rowing

5. Sprints or speed work

Running fast for short periods of time—about 30 seconds or less—is an anaerobic type of exercise that can count toward your weekly cardio. And speed work is similar, but you may also be running backwards, or laterally side to side. “Sprints and speed work improve balance, power, strength, and running efficiency, utilizing fast twitch muscle fibers, which tend to be less functional as we age,” Maianu says. That said, speed work might not be the best choice for you if you’re typically sedentary since you’ll need to work up your strength to partake without injury.

6. Low intensity, steady state cardio

This method of cardio gets your heart rate up to an aerobic level, or 60 to 85 percent of your max heart rate, and keeps it there for 30 minutes or more—think a long brisk walk on the treadmill or the elliptical. If your doctor has approved you for exercise, steady state cardio is a great place to begin, even if you’ve never done cardio before, Maianu says.

RELATED: 3 Ways to Walk

7. Tabata

Discovered by a doctor and team of researchers in Japan, Tabata, which is an intense and precise type of HIIT, is all about intensity and precise timing: It involves 20-second bouts of exercise followed by 10 seconds of rest. “It raise the heart rate between 85 and 100 percent of its max,” Maianu says, adding that the benefits include an after-burn effect, improvements in your body’s ability to metabolize sugar, and the ability to improve your fitness level efficiently. Again, because of its intensity, this type of training is best suited for those who are already familiar with cardio and interval training. When taking part, three to four times a week with at least one day of rest between training sessions is ideal.

RELATED: 5 Reason to Try HIIT Workouts

This playground pastime is back! In addition to improving your balance and coordination, jumping rope burns more than 10 calories per minute. You’ll also tone the muscles in your back and arms as you swing the rope.

4. Cycling

Cycling is another great low-impact exercise that you can do, even when you’re on your period. Stationary bikes allow you to change the gears to increase or decrease resistance so you can adjust the intensity of your workout. A spin class at your local gym can burn up to 600 calories in a 45-minute session.

5. Rowing

The rowing machine may be less common than the treadmill at the gym, but that doesn’t make it any less effective at giving you a full-body cardio workout. A moderate rowing session uses 80% of the muscles in your body and burns up to 300 calories in 30 minutes.

6. Burpees

Burpees combine jumping, squats, and planks in one swift movement. A great warm up on their own, burpees can also be combined with an interval training routine to mix up your cardio exercises.

7. Rollbacks

Rollbacks are a form of abdominal exercise that can be done on the mat or on an exercise ball. You can do rollups with free weights in your hands to tone your upper body as well. Try doing 5–10 reps and 2–3 sets of rollbacks as part of your cardio routine.

8. Mountain climber push-ups

Mountain climbers are like running on the spot — but from a push-up position. Alternate bringing the knees into the chest and add 5–10 pushups in between sets. Combine mountain climbers, rollbacks, and burpees for an intense cardio circuit workout!


High-intensity interval training (HIIT) is a workout that combines short bursts of different bodyweight exercises like burpees, pushups, and mountain climbers with cardio exercises like jump rope, running, or rowing. With HIIT, you want to alternate between high-intensity and low-intensity exercises for several sets.

On top of being the best cardio workouts, many of these exercises are ones that you can do just about anywhere! As with any type of exercise, be sure to talk to your doctor before starting a new activity or training program if you are pregnant, over 40, or have a health condition or injury. Stay hydrated throughout your workout and wind down with gentle stretching exercises to alleviate stiff muscles.

Check out for more great tips on having a healthy and active lifestyle!

Endurance exercise is one of the four types of exercise along with strength, balance and flexibility. Ideally, all four types of exercise would be included in a healthy workout routine and AHA provides easy-to-follow guidelines for endurance and strength-training in its Recommendations for Physical Activity in Adults.

They don’t all need to be done every day, but variety helps keep the body fit and healthy, and makes exercise interesting. You can do a variety of exercises to keep the body fit and healthy and to keep your physical activity routine exciting. Many different types of exercises can improve strength, endurance, flexibility, and balance. For example, practicing yoga can improve your balance, strength, and flexibility. A lot of lower-body strength-training exercises also will improve your balance.

Also called aerobic exercise, endurance exercise includes activities that increase your breathing and heart rate such as walking, jogging, swimming, and biking.

Endurance activity keeps your heart, lungs and circulatory system healthy and improves your overall fitness. As a result, people who get the recommended regular physical activity can reduce the risk of many diseases such as diabetes, heart disease and stroke.

How much do I need?

Building your endurance makes it easier to carry out many of your everyday activities. If you’re just starting out on an exercise routine after being sedentary, don’t rush it. If you haven’t been active for a long time, it’s important to work your way up over time.

Start out with 10-15 minutes at a time and then gradually build up. The AHA recommends that adults get at least 150 minutes (2 1/2 hours) of moderate to vigorous activity per week. Thirty minutes a day five days a week is an easy goal to remember. Some people will be able to do more. It’s important to set realistic goals based on your own health and abilities.

Making Progress

When you’re ready to do more, you can build on your routine by adding new physical activities; increasing the distance, time, or difficulty or your favorite activity; or do your activities more often. You could first build up the amount of time you spend doing endurance activities, then build up the difficulty of your activities. For example, gradually increase your time to 30 minutes over several days to weeks by walking longer distances. Then walk more briskly or up hills.

Examples of endurance exercise:

  • Walking briskly
  • Running / jogging
  • Dancing
  • Swimming
  • Biking
  • Climbing stairs at work
  • Playing sports such as tennis, basketball, soccer or racquetball

What if I’m recovering from a cardiac event or stroke?

Some people are afraid to exercise after a heart attack. But regular physical activity can help reduce your chances of having another heart attack.

The AHA published a statement in 2014 that doctors should prescribe exercise to stroke patients since there is strong evidence that physical activity and exercise after stroke can improve cardiovascular fitness, walking ability and upper arm strength.

If you’ve had a heart attack or stroke, talk with your doctor before starting any exercise to be sure you’re following a safe, effective physical activity program.

What Is Cardiovascular Training?

Gym & Workouts

‘Cardio’, ‘CV session’ and ‘cardiovascular workouts’, are all common expressions referring to cardiovascular training. But what exactly is cardiovascular training and how much of it should you be doing?

‘Cardio’, ‘CV session’ and ‘cardiovascular workouts’, are all common expressions referring to cardiovascular training. But what exactly is cardiovascular training and how much of it should you be doing?

Cardiovascular (CV) training

The dictionary definition for CV training is: ‘physical conditioning that exercises the heart, lungs and associated blood vessels’. In other words, when you do a cardio session, you’re giving your heart, lungs and circulatory system – in addition to any other muscle groups that you use – a good workout. Cardio exercise is extremely important because this system is effectively your body’s engine – and without a strong engine you’ll be going nowhere, no matter how good your bodywork is!

How do I measure my CV system?

There are two useful ways to measure the efficiency of your CV system:

  • Resting heart rate (RHR)

Your RHR is the number of times your heart beats in 60 seconds – with each beat a single contraction of your heart as it pumps blood around your body. The lower your RHR is, the more blood your heart can pump in a single contraction and effectively the stronger it is. The average value for an adult’s RHR is 72 beats per minute, but with cardiovascular training that figure will reduce, providing you with a measure of your improvement. Elite athletes can have extremely low RHR values – for example the former double Olympic gold medallist Sebastian Coe reputedly had a RHR of 29!

  • Blood pressure (BP)

Blood pressure has two values, which are usually displayed as two figures, one above the other – for example 120/70. The upper figure is the systolic pressure and is the pressure when the heart contracts or pumps blood out, while the lower figure is the diastolic pressure and is the pressure when the heart is relaxed. Your target figure for your BP should be no higher than approximately 140/85 – and, similarly to RHR, CV exercise will lower your BP, which will provide you with a measure of your CV health.

Different types of CV exercise

There are many different types of CV exercise, but the most effective CV exercises are those that use the largest muscle groups in the body and require you to support your own bodyweight while exercising. So, walking, jogging and running, while excellent fat burning exercise, are excellent for your CV workout because they fulfil both criteria: they use the large muscles of the legs and you have to stand up throughout your workout.

On the other hand, a hand-cycling machine – which you could find in a gym – is a far less effective CV exercise, because you will be using the smaller muscles of the arms and will be seated throughout your workout. The following list will give you some ideas for your CV workout:

Swimming; cycling; rowing; aerobics; circuit training; walking; jogging; running; dancing; using gym machines such as a stepper, treadmill, rower, or cross-trainer; and team sports such as football.

Cardio training benefits

In addition to keeping your heart and lungs in shape, CV training burns calories and is your primary tool for weight management. For example, walking, jogging and running burn approximately 100 calories per mile covered – so walking two miles each way to and from work will burn off the equivalent of a half a kilogram of body fat in a fortnight! Also, you will tone up the muscles employed – usually the legs – and release endorphins during exercise. Endorphins are the ‘feel-good’ hormones that give you that buzz after a workout.

How much cardio exercise should I do?

To get health and fitness benefits, you should aim to do at least 30 minutes of continuous CV exercise five times per week. Although this may seem like a lot, if you factor in activities such as walking as well as specific exercise sessions, it is easily achievable. Statistics show that 17 per cent of car journeys are less than one mile – which include trips to drop the kids off at school or going to the local shops – whereas a mile can easily be covered in 15 minutes on foot and will give you numerous health and fitness benefits.

Cardio exercise precautions

If you are at all unsure about starting a CV exercise programme or have not exercised for some time, then get the all clear from your doctor before you begin. There are also certain forms of CV training that are unsuitable for some people – for example, if you suffer from arthritis or joint problems then impact activities such as jogging and running will not be good for you. Also, asthmatics will find CV exercise easier to do in moist, warm conditions – so swimming in a heated, indoor pool is ideal for people who suffer from asthma.

To fully exercise your CV system you need to carry out at least five sessions per week, but you should always factor in one complete rest day each week to avoid excessive fatigue and overtraining, and to allow your body to recover and rebuild stronger.

Your cardiovascular workout

Keeping your heart and lungs in good shape has to be a priority for your fitness programme, because CV training is essential for long-term health and fitness. In addition to the whole host of health and fitness benefits that you can gain from regular cardio exercise, CV workouts can be fun and enjoyable, leaving you feeling great for hours afterwards! The ‘runner’s high’ is a well known phenomenon that runners often experience after a session – but this can equally be experienced through any of the different forms of CV activity.

The Three Metabolic Energy Systems

We usually talk of energy in general terms, as in “I don’t have a lot of energy today” or “You can feel the energy in the room.” But what really is energy? Where do we get the energy to move? How do we use it? How do we get more of it? Ultimately, what controls our movements? The three metabolic energy pathways are the phosphagen system, glycolysis and the aerobic system. How do they work, and what is their effect?

Albert Einstein, in his infinite wisdom, discovered that the total energy of an object is equal to the mass of the object multiplied by the square of the speed of light. His formula for atomic energy, E = mc2, has become the most recognized mathematical formula in the world. According to his equation, any change in the energy of an object causes a change in the mass of that object. The change in energy can come in many forms, including mechanical, thermal, electromagnetic, chemical, electrical or nuclear. Energy is all around us. The lights in your home, a microwave, a telephone, the sun; all transmit energy. Even though the solar energy that heats the earth is quite different from the energy used to run up a hill, energy, as the first law of thermodynamics tells us, can be neither created nor destroyed. It is simply changed from one form to another.

ATP Resynthesis

The energy for all physical activity comes from the conversion of high-energy phosphates (adenosine triphosphate—ATP) to lower-energy phosphates (adenosine diphosphate—ADP; adenosine monophos-
phate—AMP; and inorganic phosphate, Pi). During this breakdown (hydrolysis) of ATP, which is a water-requiring process, a proton, energy and heat are produced: ATP + H2O —© ADP + Pi + H+ + energy + heat. Since our muscles don’t store much ATP, we must constantly resynthesize it. The hydrolysis and resynthesis of ATP is thus a circular process—ATP is hydrolyzed into ADP and Pi, and then ADP and Pi combine to resynthesize ATP. Alternatively, two ADP molecules can combine to produce ATP and AMP: ADP + ADP —© ATP + AMP.

Like many other animals, humans produce ATP through three metabolic pathways that consist of many enzyme-catalyzed chemical reactions: the phosphagen system, glycolysis and the aerobic system. Which pathway your clients use for the primary production of ATP depends on how quickly they need it and how much of it they need. Lifting heavy weights, for instance, requires energy much more quickly than jogging on the treadmill, necessitating the reliance on different energy systems. However, the production of ATP is never achieved by the exclusive use of one energy system, but rather by the coordinated response of all energy systems contributing to different degrees.

1. Phosphagen System

During short-term, intense activities, a large amount of power needs to be produced by the muscles, creating a high demand for ATP. The phosphagen system (also called the ATP-CP system) is the quickest way to resynthesize ATP (Robergs & Roberts 1997). Creatine phosphate (CP), which is stored in skeletal muscles, donates a phosphate to ADP to produce ATP: ADP + CP —© ATP + C. No carbohydrate or fat is used in this process; the regeneration of ATP comes solely from stored CP. Since this process does not need oxygen to resynthesize ATP, it is anaerobic, or oxygen-independent. As the fastest way to resynthesize ATP, the phosphagen system is the predominant energy system used for all-out exercise lasting up to about 10 seconds. However, since there is a limited amount of stored CP and ATP in skeletal muscles, fatigue occurs rapidly.

2. Glycolysis

Glycolysis is the predominant energy system used for all-out exercise lasting from 30 seconds to about 2 minutes and is the second-fastest way to resynthesize ATP. During glycolysis, carbohydrate—in the form of either blood glucose (sugar) or muscle glycogen (the stored form of glucose)—is broken down through a series of chemical reactions to form pyruvate (glycogen is first broken down into glucose through a process called glycogenolysis). For every molecule of glucose broken down to pyruvate through glycolysis, two molecules of usable ATP are produced (Brooks et al. 2000). Thus, very little energy is produced through this pathway, but the trade-off is that you get the energy quickly. Once pyruvate is formed, it has two fates: conversion to lactate or conversion to a metabolic intermediary molecule called acetyl coenzyme A (acetyl-CoA), which enters the mitochondria for oxidation and the production of more ATP (Robergs & Roberts 1997). Conversion to lactate occurs when the demand for oxygen is greater than the supply (i.e., during anaerobic exercise). Conversely, when there is enough oxygen available to meet the muscles’ needs (i.e., during aerobic exercise), pyruvate (via acetyl-CoA) enters the mitochondria and goes through aerobic metabolism.

When oxygen is not supplied fast enough to meet the muscles’ needs (anaerobic glycolysis), there is an increase in hydrogen ions (which causes the muscle pH to decrease; a condition called acidosis) and other metabolites (ADP, Pi and potassium ions). Acidosis and the accumulation of these other metabolites cause a number of problems inside the muscles, including inhibition of specific enzymes involved in metabolism and muscle contraction, inhibition of the release of calcium (the trigger for muscle contraction) from its storage site in muscles, and interference with the muscles’ electrical charges (Enoka & Stuart 1992; Glaister 2005; McLester 1997). As a result of these changes, muscles lose their ability to contract effectively, and muscle force production and exercise intensity ultimately decrease.

3. Aerobic System

Since humans evolved for aerobic activities (Hochachka, Gunga & Kirsch 1998; Hochachka & Monge 2000), it’s not surprising that the aerobic system, which is dependent on oxygen, is the most complex of the three energy systems. The metabolic reactions that take place in the presence of oxygen are responsible for most of the cellular energy produced by the body. However, aerobic metabolism is the slowest way to resynthesize ATP. Oxygen, as the patriarch of metabolism, knows that it is worth the wait, as it controls the fate of endurance and is the sustenance of life. “I’m oxygen,” it says to the muscle, with more than a hint of superiority. “I can give you a lot of ATP, but you will have to wait for it.”

The aerobic system—which includes the Krebs cycle (also called the citric acid cycle or TCA cycle) and the electron transport chain—uses blood glucose, glycogen and fat as fuels to resynthesize ATP in the mitochondria of muscle
cells (see the sidebar “Energy System Characteristics”). Given its location, the aerobic system is also called mitochondrial respiration. When using carbohydrate, glucose and glycogen are first metabolized through glycolysis, with the resulting pyruvate used to form acetyl-CoA, which enters the Krebs cycle. The electrons produced in the Krebs cycle are then transported through the electron transport chain, where ATP and water are produced (a process called oxidative phosphorylation) (Robergs & Roberts 1997). Complete oxidation of glucose via glycolysis, the Krebs cycle and the electron transport chain produces 36 molecules of ATP for every molecule of glucose broken down (Robergs & Roberts 1997). Thus, the aerobic system produces 18 times more ATP than does anaerobic glycolysis from each glucose molecule.

Fat, which is stored as triglyceride in adipose tissue underneath the skin and within skeletal muscles (called intramuscular triglyceride), is the other major fuel for the aerobic system, and is the largest store of energy in the body. When using fat, triglycerides are first broken down into free fatty acids and glycerol (a process called lipolysis). The free fatty acids, which are composed of a long chain of carbon atoms, are transported to the muscle mitochondria, where the carbon atoms are used to produce acetyl-CoA (a process called beta-oxidation).

Following acetyl-CoA formation, fat metabolism is identical to carbohydrate metabolism, with acetyl-CoA entering the Krebs cycle and the electrons being transported to the electron transport chain to form ATP and water. The oxidation of free fatty acids yields many more ATP molecules than the oxidation of glucose or glycogen. For example, the oxidation of the fatty acid palmitate produces 129 molecules of ATP (Brooks et al. 2000). No wonder clients can sustain an aerobic activity longer than an anaerobic one!

Understanding how energy is produced for physical activity is important when it comes to programming exercise at the proper intensity and duration for your clients. So the next time your clients get done with a workout and think, “I have a lot of energy,” you’ll know exactly where they got it.

Metabolic Energy Systems 101

At certain points during exercise your body uses the three energy systems (that we know about as of now…there may be more energy systems that we don’t yet understand) APT-Phosphocreatine, Anaerobic Glycolysis and Aerobic. Your body converts carbohydrates, and in fasting situations fatty acids and amino acids, into glucose. Glucose will then be broken down through Glycolysis to make ATP (energy). This can be done anaerobically (without oxygen) and aerobically (with oxygen). When we are working out at a high enough intensity to cause rapid breathing (above 75% max heart rate) we are working anaerobically and challenging our phosphagen system and glycolysis. When we are working out aerobically (under that 75%) our body can breakdown glucose and perform many other aerobic metabolic processes that keep our body fueled with ATP. Glucose is then taken into the cell and converted into a chemical energy molecule called adenosine triphosphate, or ATP.

Your muscle has a small amount of ATP floating around that it can use but not a lot- only enough to last for about the first three seconds of an exercise. To replenish these levels, the body uses a high-energy phosphate compound called creatine phosphate (you may have heard of the supplement creatine-monohydrate…this is what it is used for) to make more ATP. This cycle keeps adding a phosphate to make ATP once it has been used for energy. The ATP and creatine phosphate together are called the phosphagen system. The phosphagen system can supply energy needs to a working muscle for about 10 seconds before needing to go through this conversion cycle again.

Analysis of the Rest Periods

Perhaps you’ve already asked yourself what the benefit is of a rest period, when to use it and why. It is easy to get confused concerning this topic, but the answer is related to goal and intensity level. Rest periods are an amount of time between sets ranging from 30 seconds to 5 minutes. According to American College of Sports Medicine, ACSM, Resources for the Personal Trainer, 3rd edition, rest periods can be categorized using this scale:

  • Very short rest periods- 1 minute or shorter
  • Short rest periods- 1-2 minutes
  • Moderate rest periods- 2-3 minutes
  • Long rest periods- 3-4 minutes
  • Very long rest periods- 5 minutes or longer

According to research, it takes approximately 2.5 to 3 minutes for complete resynthesis of APT stores and 8 minutes for complete creatine phosphagen repletion after an intense exercise (both translate to anaerobic energy). There is increased use of both glycolytic (aerobic and anaerobic breakdown of glucose as energy) and ATP-CP during high intensity. Glycogen stores and blood glucose will lower in addition during high intensity, which equates to multiple metabolic processes (aerobic and anaerobic) being stressed.

According to National Strength and Conditioning Association, NSCA, The Essentials of Strength Training and Conditioning, 3rd edition, phosphagen concentrations during high-intensity training anaerobic exercise can decrease (50-70%) during the first 5-30 seconds of high-intensity and can be depleted to almost eliminated upon complete exhaustion. On the other hand, to improve the body’s bicarbonate, phosphate, blood and muscle buffering systems, less rest is required. So, which yields greater benefits?

Strength athlete/ power= optimal rest period is 3 to 5 minutes.
A strength athlete will train explosive (fast, powerful movements), low repetition activities of short duration. It is also common to see plyometrics (drills that increase speed, agility and quickness) incorporated into the program. A strength athlete (includes power lifters and athletes involved in sports that require high intensity, short bursts) is usually concerned with performance in relation to maximal power that can be produced. This type of routine focuses on strength and not hypertrophy or endurance. This high intensity style training will increase the heart rate (utilizing and depleting all the anaerobic energy within the set) and will increase the release of testosterone to produce maximal muscular output. The recommended rest period for anaerobic activity should be from 3 to 5 minutes.

Muscle growth/ endurance conditioning= optimal rest period is 30 to 60 seconds.
For increased hypertrophy as well as endurance sport conditioning training, the workout should have a slower tempo, 8- 12 repetition range, and the goal is to achieve close to maximal force output by a muscle over a time period. The typical rest period for this type of programming is between 30 to 60 seconds, or a 1:1 ratio of work to rest. The body buffers the effect of increased lactate in the muscles. This type of training increases production of Human Growth Hormone and thus hypertrophy of the muscle.

Circuit/ superset training= optimal rest period is 30 seconds.
Circuit or superset training is designed to combine the effects of strength and aerobic training, so rest periods are minimal from 30 seconds to a 1:1 ratio, and thus limits max output. This type of training can have multiple benefits (sometimes less measurable in strength, but definitely measurable in aerobic capacity), and can be useful in weight loss and toning. According to research, strength gains are limited to only 30-50% the benefit of strength training.

One study done by NSCA in the Journal of Strength and Conditioning Research, Effects of Different Weight Training Exercise/Rest Intervals on Strength, Power, and High Intensity Exercise Endurance, tested if short rest periods between sets enhances high intensity exercise endurance (HIEE). Their findings concluded that sufficient rest between sets are more likely to lead to greater increase in maximum strength and performance; intensity has great importance in relation to performance (especially concerning maximum strength); and short rest periods have less positive effect on HIEE than incorporating additional sets or repetitions.

So, which routine and rest period is best for you? Many certification bodies recommend a systematic approach to periodization generally consisting of a strength base, followed by power, and then a recovery phase. Each of these should have a different intensity and rest period associated with them. Remember your approach to programming should be focused on stimulation and finding challenge in the activity.

For more information, please contact Amber Walz.

Fitness Advice, Health News, Sports Conditioning

Athletic, club, gym, health, Personal Trainer, Seattle, Training

“Regardless of the type of effort, the body never closes off all energy systems completely.”

Learn about the three major systems are energy:

  1. Anaerobic – Phosphocreatine (PCr) System (ATP; triphosphate, as in three phosphates)
  2. Glycolytic or Lactic Acid System
  3. Aerobic System

The body draws on all three, regardless of the type of effort, never closing one off completely. They merely change in the percentage and amount of energy they contribute depending on the duration and intensity of the effort.

Before we look at these systems in more detail we can get an understanding of how they are used in cycling via Dr. Andy Coggan’s Power Levels. If you’re not familiar with these levels, they are a way of categorising how intense an effort is, which dictates how long the effort will last and which systems will predominantly supply energy for the effort.

There are a few variations out there, but for cycling with power – Coggan’s Power Levels stand out as the most popular, or at least the most publicized. There are 7 levels or zones each representing an intensity and time frame and now an energy system.

Zones 1-3 represent the aerobic system.

Z1 / <55% Active Recovery / 70-80 years

Z2 / 56-75% Endurance / 2.5 hours to 14 days

Z3 / 76-90% Tempo / 2.5-8 hours

Zones 4-6 represent the lactic system.

Z4 / 91-105% Lactate Threshold / 10-60 minutes

Z5 / 106-120% V02 Max / 3-8 minutes

Z6 / >120% Anaerobic Capacity / 30 seconds to 2 minutes

Zone 7 stands out on its own and represent the ATP system.

Z7 / N/A Neuromuscular Power / 5-15 seconds

And that’s where we are going to start:

Energy System 1: Anaerobic – Phosphocreatine (PCr) System

The first phase is called the ATP- CPr (Adenosine Triphosphate)- (Phosphocreatine) system. ATP is stored in all cells, particularly muscles. It is the only system that doesn’t require a blood supply and has no by products.

There are not many steps in the chemical reactions that make up the ATP-PCr system. The reactions can take place in the absence of oxygen and phosphocreatine is a relatively high energy molecule. As a result, the ATP-PCr system can provide a lot of energy quickly but only for immediate and short (10s) maximum intensity efforts.

In a sense, it is free energy because the body stores ATP to make it available for immediate use, however, you can only use it once and it needs recovery time to restore the storage. Once you have depleted you Phosphocreatine stores in a sprint it can take as long as 5 minutes to restore them to their resting levels, ready to sprint again. Making it a high rate – low capacity system.

Energy System 2: Anaerobic – Lactic Acid System (LA)

The next major phase is called the Lactic (LA) system. After the 20 seconds of the ATP-PCr system, the body requires another ingredient– muscle glycogen (glucose) to be added to continue.

This system breaks down carbohydrate, a fuel in limited supply in the body, to produce medium amounts of power for medium amounts of time. The energy is produced without oxygen using carbohydrate > sugar > glucose > glycogen > ATP.

The body’s stores around 500 grams worth of carbohydrate in the tissues of the liver and muscles in the form of glycogen. This amount of energy would fuel approximately 2000 Kilojoules of mechanical work on the bike, as recorded by a power meter.

Regardless of how long an effort is, carbohydrate is always initially broken down through a chemical reaction called anaerobic glycolysis. Oxygen is not required for this reaction and whilst only about 5% (2 ATP molecules) of the energy potential of a glucose molecule can be realised the energy is liberated quickly, so this energy system is well suited to high intensity efforts greater than 10 seconds to 2 minutes.

Because anaerobic glycolysis can only supply short efforts, it only makes a small dent in the 2000 Kilojoules of stored carbohydrate available, so the time limitation is related to the chemical processes involved in anaerobic metabolism and their interaction with the body, rather than a lack of availability of carbohydrate.

Its by-product, lactic acid, comes from the breakdown of the glucose released from the muscles. Most cyclists have heard of lactate or lactic acid. Lactate is not a waste product but is actually an important part of anaerobic and aerobic metabolism.

During high intensity efforts lactate is produced in greater amounts than can be removed and contrary to popular belief, fatigue may not simply be the result of lactic acid accumulation – there is a lot of misunderstanding around this molecule. For one, lactate does not cause muscle soreness. Another, fatigue from exercise is not due simply to lactate accumulation.

Energy System 3: Oxidative (Aerobic) System

The first or third system is the Oxidative phase. In this phase, as the term indicates you are using oxygen to fuel the breakdown of carbohydrates first, free fatty acids second and if the exercise continues long enough -protein. Whereas, the previous systems have related to higher intensity work (or power) the aerobic system is more for moderate or low intensity work, but of longer duration.

It can draw on your stores of glucose but only for ~90 minutes at max. This is why you need to replenish your glucose stores with CHO during your ride.

The oxidative system should be developed to aid in the lactic system. The development of the aerobic system aids in lactate removal so that you can tolerate more lactate.

It is only able to produce a relatively small amount of energy, so cannot produce enough energy for any sprinting, but can produce power for extended periods of time, making it the predominant system used during any endurance ride.

What Does Mean For You?

No matter if you’re a road rider or an MTB racer you use all their energy systems to ride in all types of terrains. Individually you have strengths and weaknesses for specific durations and intensities relative to others. Whether it’s being a better sprinter than long climbs, or hammering short-steep hills your energy systems can be improved through training.

As mentioned before when on the bike all systems are providing a portion of energy depending on the intensity of work being done. This can actually be tested in a lab. Similar to the equipment used to analyses the Fatmax test.

If you were to do a 120 second sprint test. The first 10-15 seconds is fueled almost entirely by the PCr system, producing a huge burst of power, but very quickly fatiguing. After around 10 seconds the Phoscreatin system is completely exhausted and the lactate acid system starts to kick in. By 30 seconds the LA system has fully taken over but rapidly starts to fatigue as lactate acid accumulates. By 40 seconds, the aerobic system has begun to kick in as oxygen has made it to the working muscle and begins to assist with the aerobic contribution of energy production.

You can test this without a lab. But really you’re just better off doing a Power Profile Field Test. This will highlight the main areas that need working on because you aren’t producing enough power or you’re predisposed to one type of event.

What about training? Training should address all of your energy systems, combining efforts from sprints to long rides over multiple hours.

The awareness of your energy systems may also come in handy when racing. Anytime you are on the bike ask yourself ‘where is my energy coming from’ or ‘what energy have I burnt recently?’ Put it on the Focus Room Checklist and base your decisions on the % of W you are putting out over specific durations. Know where you are drawing energy from will help you to know how much you might have in reserve. Or how long you should rest before you can go again at max capacity.

This is still a guessing game at this stage and links in with the idea of ‘matches’ and the work on W Prime / Functional Reserve Capacity. These are only new ideas (relatively) and there isn’t much literature around yet but there’s no harm in trying to work out what works for you, and how you can best optimise your energy systems.


  • Ted King
  • Impact of training intensity distribution on performance in endurance athletes
  • BMC Racing Team Pre-Season Training

Different types of cardio

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