Six Week Shred: Torch Fat With HIIT 100s

If we had a dollar for every well-intentioned person who’s centered his or her fat-burning efforts around low- to moderate-intensity cardio sessions, we could make Fort Knox our summer retreat. This “I’m trying to lose weight, so I’m just doing cardio” attitude has become epidemic, as people waste countless hours on ellipticals, treadmills, and stationary bikes, with very little to show for it. The results they’re after, of course, are washboard abs and an overall leaner physique, which is best accomplished through high-intensity lifting at appreciable volumes.

Enter HIIT 100s, M&F’s most efficient program to date for whittling away stubborn body fat in a short period of time. Stick to the following workouts for a full six weeks while keeping your diet clean, and that shredded body you could never achieve through endless cardio sessions will be yours very soon.

Greatest HIITs

You’re probably familiar with high-intensity interval training (HIIT). When it comes to cardio, HIIT is definitely the best way to strip off body fat, to the extent that there’s literally no reason to hop on a treadmill and run at a steady pace for 30 or more minutes unless you’re an endurance athlete. And if you’re reading this magazine, chances are you don’t desire the physique of a marathoner.

For those of you who aren’t familiar with HIIT, it involves intervals of high-intensity exercise (such as running at 90% of your max heart rate) followed by low intensity (walking at a moderate pace) or complete rest. This is in sharp contrast to the typical steady-state cardio most people do at a moderate intensity, such as walking on a treadmill at 60-70% of their max heart rate.

HIIT was originally developed by track coaches to train runners, but it has crossed over to the fitness industry due to its fat-burning benefits confirmed many times over in scientific studies (see “HIIT Findings”). A lot of these studies found that subjects performing HIIT burned significantly more body fat—and in less time—than those who did steady-state cardio programs.

The major reason HIIT works so well for dropping body fat is due to the greater calorie burn (or EPOC—excess post-exercise oxygen consumption) that’s maintained after the workout is over. In other words, you burn more calories and more body fat while you’re sitting around doing nothing. In addition to this increase in resting metabolism, HIIT is effective at enhancing the mechanisms in muscle cells that promote fat burning and blunt fat storage.

Volume 100

When most people think of HIIT they think of it as applicable only for cardio, yet it can also be used in weight training. After all, weight training itself is a form of HIIT—you do a set with all-out effort, rest, then do another set, rest, and repeat. Resting two to three minutes between sets, however, is too long for a training session to be considered an effective form of HIIT. But all you have to do is shorten rest periods and you’re doing a kind of HIIT that burns fat.

For this HIIT 100s program, I’ve combined HIIT not only with weights but also with two very popular, intense, and effective weight-training techniques: German volume training (GVT) and Hundreds training. With GVT, aka 10×10, you do 10 sets of 10 reps on a given exercise. Hundreds, as the name implies, involves doing 100-rep sets. With Hundreds, you’ll do 10 sets of 10 reps for one exercise per muscle group. Sounds the same as GVT, right? Not exactly.

HIIT is incorporated via the rest periods between those 10 sets. You’ll start with just 60 seconds between sets at the beginning of the program and progressively drop rest periods by 10 seconds over six weeks until you have no rest and are doing 100 reps straight through.

The two forms of training are technically different, but late in the HIIT 100s program, when you’re resting only 10 or 20 seconds between sets of 10, there’s little to distinguish them as far as the toll they take on your body.

Method To The Madness

The following workouts are simple to follow, just not very easy to do. For each major muscle group, after following the HIIT 100s protocol on your first exercise, you’ll do three more sets to failure of the same exercise using your 10-rep max (10RM). Of course, after doing 10 sets of 10 reps, you’ll no longer be able to complete 10 full reps with your 10RM weight—probably more like 5-7 reps. On the third set, you’ll do a dropset with the same weight you used for HIIT 100s (50% of your 10RM) and do as many reps as possible.

Three sets of one or two more exercises and you’ll be done with that muscle group for the day. Rest between all sets following the HIIT 100s exercise is limited to one minute to maximize fat burning. You’ll follow the muscle group-specific weight training with one last dose of HIIT 100s using a full-body exercise such as barbell or dumbbell cleans; kettlebell swings; barbell or dumbbell deadlifts; barbell, dumbbell, or kettlebell snatches; or my own unique lift known as the dead/curl/press.

On HIIT 100s sets during Weeks 1-3, when rest periods are 30 seconds or more, perform the first three sets of 10 as fast and explosively as possible. This will help build more muscle power and strength, despite using such light weight. On Sets 4-6, keep the movement slow and controlled, focusing on the contraction and squeezing each rep at the top for one to two seconds. This helps establish a strong mind-muscle connection, which is critical for muscle size, shape, and separation.

During Weeks 4-6, when rest periods are down to 20 seconds or less, your goal is to simply complete the 100 reps. Don’t worry about rep speed or control; just get the reps done with the best form possible while your muscles are on fire.

Get Started

On HIIT 100s exercises, select a weight that’s equal to 50% of what you could normally do for 10 reps. Don’t worry about going too heavy. If you can’t complete all 10 reps before the eighth set, drop the weight by 5-10 pounds. If you can’t complete 10 reps during or after the eighth set, finish all 10 sets doing as many reps as possible for each.

The next time you train that muscle group, decrease the starting weight by 5-10 pounds. If any of the HIIT 100s exercises are new to you, you’ll need to spend some time figuring out how much weight you can do for 10 reps. The week before you start the HIIT 100s program, work these exercises into your training to get a gauge on appropriate weights. When estimating your 10RM, be sure to do the HIIT exercise first for that muscle group.

For example, if you don’t know what your 10RM is on the bench press, do bench as the first exercise in your chest workout, aiming for a weight that allows you to complete exactly 10 reps, then follow with your typical chest routine.

Hundreds Of Benefits

While the major benefit of this program is rapid fat loss, the fringe benefits are just as impressive. Even though the weights you use will need to be light, your muscles will still get the signal to grow. HIIT 100s make a very light weight brutally difficult to move. This pushes muscle fatigue to new levels, which stimulates the release of muscle-building hormones.

Another obvious benefit of doing 100 reps with progressively shorter rest periods is increased muscle endurance, which will boost your conditioning—a big advantage if you play sports. Even if you’re not an athlete, this benefit will ring loud and clear in your workouts.

When you go back to your regular regimen, where you’re resting a couple of minutes between sets, your muscle recovery will be quicker, thus allowing you to get more reps with the same weight on successive sets and delivering a greater stimulus.

2-Weeks Worth Of Workouts

Week 1

Workout 1: Chest/Back/Abs 1 10 sets, 10 reps (60 sec rest, 50% 10RM) 3 sets, Failure 10RM from test (On the last set, do a dropset by reducing the weight to the same amount you)+ 9 more exercises

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Workout 2: Legs/Triceps/Calves 1 10 sets, 10 reps (60 sec rest, 50% 10RM) 3 sets, Failure 10RM from test (On the last set, do a dropset by reducing the weight to the same amount you used for HIIT 100s and doing as many reps as possible to failure.) + 9 more exercises

The Strength HIIT Workout That Burns Calories for Hours

Repeat after us: Weights are not the enemy. Lifting weights won’t bulk you up-it will help you build strength and boost your metabolism. Combine strength training with HIIT, and you have possibly the best body-blasting workout there is. Sarah Kusch, a personal trainer at Equinox in Santa Monica, CA, designed this one with optimized interval blocks to encourage your body to burn calories post-workout by entering into a state of EPOC (excess post-exercise oxygen consumption). And who doesn’t want to burn more calories outside the gym?

How it works: You’ll need a set of medium or heavy dumbbells and an exercise mat. Follow along with the video to work through the five-minute dynamic warm-up, 24-minute workout, and a five-minute mobility and static stretch cool-down. During block one and block three, push yourself at 80 percent of your maximum effort. During block two, go at 90 percent.


Good Morning: Stand with feet wider than hip-width apart. Hinge forward at the hips, until torso is parallel, then squeeze glutes to stand.

Isolated Squat: Stand with feet wider than hip-width apart. Hinge at the hips and bend knees to lower into a squat. Hold.

Inchworm Windmill Reach: Stand with feet hip-width apart. With soft knees, walk hands out to a plank, then walk back, placing hands on knees. Raise right arm to the ceiling, spiraling chest open to the right. Repeat on the other side.

Lateral Lunge Reach: Stand with a wide stance. Bend the right knee to lower into a lateral lunge, tapping right toes with the left hand. Repeat on the other side.

Around-the-World: Stand with feet hip-width apart. Circle torso to the right, forward, and around, engaging right obliques at the top. Reverse direction.

Arm Circles: Stand with feet hip-width apart. Circle both arms forward, then backward.

Block 1 (80% Max Effort)

Squat Thrust Curl

A. Stand with feet hip-width apart and dumbbells in hands by sides.

B. Squat down to place dumbbells on floor and jump feet back to a high plank.

C. Jump feet back up to hands, then stand and curl the dumbbells up to shoulders, palms facing up.

D. Lower dumbbells to start. Repeat for 1 minute.

Lateral Lunge with Single-Arm Row

A. Start in a wide stance with dumbbells in hands by sides.

B. Shift weight to the right and bend right knee to lower into a lateral lunge, tapping left hand to right foot, and rowing right dumbbell up to chest.

C. Immediately shift weight to the left to repeat on the other side. Continue alternating for 1 minute.

Overhead Triceps Chop

A. Stand with feet wider than hip-width apart and dumbbells together overhead.

B. Lower dumbbells behind head, elbows pointing up. Extend arms to raise dumbbells overhead, then swing them across body to right hip, pivoting on left foot.

C. Reverse movement to raise dumbbells overhead. Repeat on the opposite side. Continue alternating for 1 minute.

Deadlift Wide Row

A. Stand with feet wider than hip-width apart and dumbbells in hands by sides.

B. Hinge at the hips and bend knees to lower into a squat with arms extended slightly forward.

C. Draw elbows back and out to the sides to row dumbbells up to chest height, engaging upper back.

D. Lower dumbbells in front of knees, then stand, pushing hips forward and bringing dumbbells by sides. Repeat for 1 minute.

Reverse Lunge with Overhead Arm Circle

A. Stand with feet together and dumbbells in hands. Elbows are tight to sides, forearms parallel to the ground, and palms facing up, pointing out to the sides.

B. Step backwards with the right foot into a reverse lunge, then circle arms overhead to tap dumbbells together, maintaining the same bend in the elbows.

C. Lower arms to return elbows to sides, then push off back foot to return to starting position. Continue alternating sides for 1 minute.

Single-Leg Deadlift Row to Single-Arm Press

A. Stand on right foot, left foot hovering off the floor, and dumbbells in hands by sides.

B. Hinge at the hips, extending dumbbells toward feet, lowering torso and lifting left leg parallel to the ground.

C. Row dumbbells up to chest with elbows tight to ribs. Lower dumbbells, then engage core to lift chest back to vertical and draw left leg into a high knee.

D. Curl right dumbbell up to shoulder, then press overhead while extending left leg forward.

E. Return to starting position. Repeat for 1 minute, then repeat on the opposite side for 1 minute.

Lat Pullover to Sit-Up

A. Lie faceup on the floor, feet planted and knees pointing toward the ceiling, holding one dumbbell extended overhead.

B. Engage core and press spine into the floor while pulling dumbbell over chest.

C. Lift torso off the floor to sit up, pressing weight directly overhead.

D. Slowly reverse movement to return to starting position. Repeat for 1 minute.

Block 2 (90% Max Effort)

Curtsy Touch

A. Stand with feet together.

B. Take a big step to the right, cross left foot behind, and lowering into a curtsy lunge to tap fingers to the floor, framing front foot.

C. Stand, reaching arms overhead and hopping sideways to land on left foot, repeating the movement on the other side.

D. Continue alternating quickly for 1 minute.

Push-Up Frog Pop

A. Stand with feet wider than hip-width apart and lower into a deep squat so hamstrings are resting on calves.

B. Place hands on the floor between feet, then jump back into high plank and lower into a push-up.

C. Hop feet outside of hands to return to the frog squat, immediately lifting hands off the floor. Repeat quickly for 1 minute.

Dip Kick Crunch

A. Start in reverse tabletop position with weight in hands and feet and hips lifted.

B. Lift right hand and left foot off ground and crunch to tap elbow to knee.

C. Tap hand and foot to the floor, then immediately kick straight left leg up to touch right hand to left toes.

D. Return to starting position, then repeat on the opposite side. Continue alternating for 1 minute.

Forearm Dolphin Kick

A. Start in a low tabletop position on elbows and knees. Hover knees a few inches off the floor.

B. Maintaining this position with left leg, kick right foot back, forming a straight line from head to heel.

C. Return to starting position, then repeat on the opposite side. Continue alternating for 1 minute.

Thruster with Jump

A. Stand with feet wider than hip-width apart and dumbbell on floor between feet.

B. Hinge at the hips and bend knees to grab dumbbell, swinging it up to chest height and thrusting hips forward.

C. Reverse motion to return dumbbell to floor, then immediately hop forward into a squat then backward to return to starting position. Repeat for 1 minute.

Triceps Push-Up Hold Tuck

A. Start in a high plank position. Lower chest until arms are bent at 90 degrees, elbows tight into sides. Hold this position.

B. Jump feet forward and out to the sides so knees are almost under hips. Hop feet back out to the push-up hold position. Repeat for 1 minute.

Block 3 (80% Max Effort):

Low Squat Curl

A. Stand with feet wider than hip-width apart, dumbbells racked on shoulders with palms facing in.

B. Lower into a deep squat, then lower dumbbells and curl weights up to shoulders, palms still facing in.

C. Press up to stand, then lower into squat to begin next rep. Repeat for 1 minute.

Static Lunge Chop Chest Press

A. Start in a lunge position with left leg forward, holding one dumbbell horizontally in both hands at chest.

B. Press dumbbell forward, then lower across body to left hip. Reverse movement to return dumbbell to chest, maintaining lunge the whole time.

C. Repeat for 30 seconds, then repeat for 30 seconds on the opposite side.

Frog Squat Knee Drive

A. Start with feet wider than hip-width apart, holding a dumbbell in a goblet squat position by chest.

B. Lower into a deep squat, then press into heels to stand. Exhale and drive left knee up, rotating torso to the left.

C. Lower left leg to return to starting position, then repeat on the opposite side. Continue alternating for 1 minute.

Side Plank Press

A. Start in a right high side plank position with feet staggered, holding a dumbbell in the left hand next to left shoulder.

B. Press dumbbell to extend left arm directly in line with shoulders. Lower to return to starting position. Repeat for 30 seconds, then repeat for 30 seconds on the opposite side.

Superman Flutter Kick

A. Lie facedown on the floor with arms and legs extended.

B. Lift arms and legs off the ground, alternating lifting right and left arm and leg.

C. Repeat for 1 minute.

Kneeling Windmill

A. Kneel on both legs with dumbbells in both hands, elbows glued to sides and palms facing up.

B. Sit back onto heels, then press hips up to return to kneeling while pressing the right hand overhead, turning palm to face out, and lowering left dumbbell by side.

C. Reverse the motion to return to starting position, then repeat on the opposite side. Continue alternating for 1 minute.

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Back and Biceps Day

  • Hyperextentions (use hyperextension bench for this)- 3 sets – 10, 8, 6 reps
  • Bent Over Barbell row – 3 sets – 10, 8, 6 reps
  • Pulldowns or narrow grip chin ups – 1 set – 8 reps
  • Barbell curls superseted with incline hammer curls – 2 sets – 8, 6 reps
  • Barbell shrugs – 2 sets – 8, 6 reps

Dorian Yates HIT Workouts

Dorian Yates is a British bodybuilding champion. He was born in Sutton Coldfield in the West Midlands in 1962. At the age of 30 in 1992 he became a World bodybuilding champion when he won Mr. Olympia. He then won a further 5 times in a row until 1997 when he also retired.

Dorian Yates has adopted and adapted the HIT principal. With HIT training the number of work reps is reduced to the bare minimum, with more weight and more intensity applied.

With the more traditional high rep approach to bodybuilding people either work a set number of reps and sets on an exercise or stop at initial failure. With HIT the aim is to fail sooner, but to put vastly more effort in to trying to work through the point of failure, i.e. it is more intense.

HIT Debate

The HIT method is still being debated. Those that use it feel very strongly that the research done by Mentzer, and subsequent research, provides proof that the system works better at building muscle. In a nutshell, with HIT training, you lift fewer reps, and in doing so you give your body more time to recover, and can actually train more often.

The research done by Mentzer showed that about 95% of muscular gains are made in the first work set, and that working to failure is the best way to generate new muscle growth. Performing the following sets does not lead to much additional muscle growth, and can potentially lead to overtraining.

Dorian Yates used the 1 set method for compound exercises. For all the big movements he would perform just one set, usually less than 8 reps. Compare this to Arnold Schwarzenegger who reportedly spent about 6 hours some days in the gym pumping iron.

Dorian is a great believer that no training system is universally applicable to all and that any system should be modified to one’s personal characteristics. We are all different and all respond to different levels of intensity in different ways.

Dorian Yate’s Stats at his Peak in 1994

  • Height: 5′ 10″ (1.78m)
  • Competitive weight: 240 lbs
  • Off-season weight: 300 lbs
  • Chest 53″
  • Arms 20″
  • Waist 44″
  • Yhigh 30″
  • Calf 20″

Dorian Yates’ Weekly HIT Workout Training Plan

Note that for each exercise only the last set is the work set. The first set, or in some cases the first two, are warm up sets. The first warm up set should be done with a weight 50% of the work set. The second warm up set should be done with a weight 70% of the work set.

1 Delts Seated dumbbell presses 1 12
1 10
1 6 – 8
Dumbbell lateral raises 1 10
1 6 – 8
One-arm cable lateral raises 1 8 – 10
Traps Dumbbell shrugs 1 12
Triceps Cable pressdowns 1 12
1 10
1 6 – 8
Lying EZ-bar extensions 1 10
1 6 – 8
One-arm Nautilus extensions 1 10
1 6 – 8
Abs Roman-chair situps 1 20
Crunches 1 20
Reverse crunches 1 20
2 Back Hammer Strength pulldowns (reverse grip) 1 12
1 10
1 6 – 8
or Nautilus pullovers (alternate each workout) 1 12
1 10
1 6 – 8
Barbell rows 1 10
1 6 – 8
One-arm hammer rows 1 6 – 8
Seated cable rows (overhand grip) 1 6 – 8
Rear delts Rear-delt Hammer Strength flyes 1 6 – 8
Bent-over lateral raises 1 6 – 8
Back extensions 1 6 – 8
Deadlifts 1 8
1 6 – 8
3 Total Rest
4 Chest Incline barbell presses 1 12
1 10
1 6 – 8
Machine seated presses 1 10
1 6 – 8
Incline dumbbell flyes 1 10
1 6 – 8
Cable crossovers 1 8 – 10
Biceps Incline dumbbell curls 1 10
1 6 – 8
Standing EZ-bar curls 1 10
1 6 – 8
Preacher machine curls 1 6 – 8
Abs Roman-chair situps 1 20
Crunches 2 20
Reverse crunches 2 20
5 Total Rest
6 Quadriceps Leg extensions 1 15
1 12
1 10 – 12
Leg presses 1 12
1 12
1 10 – 12
Hack squats 1 12
1 8 – 12
Hamstrings Lying leg curls 1 8 – 10
1 8 – 10
Stiff-leg deadlifts 1 10
Single-leg curls 1 8 – 10
Calves Standing calf raises 1 10 – 12
1 10 – 12
Seated calf raises 1 10 – 12
7 Total Rest

Keep a Weight Training Log

If the final set is too easy, just increase the weights of each set in the next session. Remember that it is important to keep a good training log if you are planning this sort of training, as it is difficult to remember where you fail and what is easy otherwise.

Keep notes on how easy or difficult each final lift was, this way you can prepare before for the next workout. The warm up set should be about half of the final lift, and the first work set should be about 75% of the final set. But really you need to find a routine that you enjoy and that is giving you results.

Some people prefer to warm up with much lighter weights and perform a couple of sets of 20 to ensure good blood flow, others ignore the warm up sets completely and start with a slightly easier 10 rep set.

Mike Mentzer developed his training methods, to eventually reduce both reps and numbers of exercises. Compare an early Mike Mentzer HIT workout to the one here.

If you plan to start a H.I.T. routines you really need to plan and split your routine to ensure you work your whole body (or the areas that require most work) over the week, and that you do not overwork the same groups which can have detrimental effects and increase the risk of injury. For more on split routines read Standard Push & Pull Split Routine.

If you prefer bodyweight resistance programs, take a look at our page on high intensity circuit training using body weight.

HIT Weight Training References and Scientific Research Papers

“Training to Failure and Beyond in Mainstream Resistance Exercise Programs“. Willardson, Jeffrey M PhD, CSCS; Norton, Layne; Wilson, Gabriel MS, CSCS. Strength & Conditioning Journal:June 2010 – Volume 32 – Issue 3 – pp 21-29 doi: 10.1519/SSC.0b013e3181cc2a3a

“Moderate Volume of High Relative Training Intensity Produces Greater Strength Gains Compared With Low and High Volumes in Competitive Weightlifters”. González-Badillo, Juan José; Izquierdo, Mikel; Gorostiaga, Esteban M. Journal of strength and conditioning research / National Strength & Conditioning Association (J Strength Cond Res) Vol. 20 Issue 1 Pg. 73-81 (Feb 2006) ISSN: 1064-8011 United States.

Dorian’s training philosophy on hos personal website –

“The age of intensity: Dorian Yates dominated bodybuilding in the 1990s —these are the training philosophies and particulars that set him apart and propelled his rule” by Julian Schmidt for Flex Magazine, May 2008 Issue.

Jon Wade studied Health Sciences at the Open University, specializing in Nutrition and Obesity. He has trained in many martial arts, including kickboxing, kung-fu and karate, has played cricket and plays badminton. He started weight training to support his martial arts during the 1990s and still lifts today. He has been researching and writing on fitness, weight training and health since 2006.

Whether you’re looking to trim your waistline or get totally ripped, combining both strength training and cardio into your workout regimen is key.

For cardio junkies, incorporating a strength-training routine can help you improve your form, endurance, and daily calorie burn. Adding muscle has the benefit of increasing the efficiency of movement, allowing you to go farther and move with more power. The added muscle also has the benefit of increasing your metabolism. Thus by adding strength training, you can break through weight-loss plateaus and/or your personal record time.

Conversely, if you are a meathead that’s always in the weight room, you will find that incorporating cardio is a more effective way of burning off body fat than weight training alone. Certain brands of cardio, like HIIT (see below), will also help you build muscle – not deteriorate it.

Combining cardio and strength training can also complement each other, even when done on the same day. That is, studies show that strength training does not negate the gains of endurance training when done on the same day. Likewise, cardio will not negate the growth of muscles when done on the same day.

To effectively combine strength training and cardio, follow one of these three strategies:

High Intensity Interval Training (HIIT)

HIIT is by far the most efficient way to burn fat, burn calories, and improve aerobic capacity. For instance, a 10-minute HIIT routine can burn as many calories as 30 minutes on the treadmill. Another study by the American College of Sports Medicine found that engaging in just two weeks of HIIT is equivalent to six to eight weeks of endurance training.

So what exactly is it? HIIT combines super high-intensity cardio with recovery intervals (like strength training exercises) at a 1:4 ratio. High-intensity intervals are at 80% of your maximum capacity, while recovery intervals are around 40% of your maximum capacity.

An example of an interval cycle can include one minute of mountain climbers, followed by one minute each of squats, deadlifts, handstand pushups, and planks. Repeat this cycle four to six times, or follow up with different 1:4 combinations.

Close Out a Weight-Training Session with 5-10 Minutes of Cardio Sprints

You can still reap the benefits of incorporating cardio by doing 5 to 10 minutes of cardio sprints after weights. This is good option for meatheads who avoid cardio because of boredom, and don’t normally get their heart rate up through aerobic exercise.

One way of doing cardio sprints is the Fartlek workout, which means “speed play” in Swedish. You combine fast-paced intervals with recovery intervals, at whatever distance and pace you want. During the recovery intervals, however, you’ll want to go slow enough to recover your breath to the point you can breathe deeply again before engaging in another sprint interval.

Train Every Major Muscle Group Once Per Week

If you are a cardio junkie looking to incorporate strength training, keep in mind you need to train every muscle group – core, legs, back, etc. – once per week. By training every muscle group, you’ll be maintaining physical balance. You’ll also be reducing your risk of injury by not over training. Muscles need between 48 – 72 hours to fully recover and grow from resistance training. Without that rest, training muscles too frequently will lead to atrophy and/or loss of strength.

One strategy is to intensely hit one major muscle group for a 30-minute workout for five out of seven days per week. Another strategy is to do a longer full-body workout, two days per week.

Either way, you can do the strength training workout alone, or before your cardio session that day. Most experts agree that strength training is best before cardio to ensure you have enough energy to perform the exercises with proper form.

Note, however, if you’re an endurance athlete, a study on endurance runners suggests you should combine the two only on days the cardio will be at “submaximal intensities.” The study found a strength training session of the lower extremities can hamper a hard run for up to 24 hours, but has no effect on light or moderate running sessions.

For more workout ideas, or to find a personal trainer in the Denver area, contact us at Shape Plus.

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Combining HIIT and weight training is not usually something that comes to mind when people think of High Intensity Interval Training (HIIT), so you may be surprised to find out just how well they go together.

Done individually, HIIT and weight training are quite demanding. When combining them, your sessions will be even more challenging than doing one alone, so you will need to take precautions to prevent injury occurring.

In this article, we will look at how to combine HIIT and weight training. We will also discuss the benefits doing so will bring and the measures you will need to take to avoid injury and burnout.

*NB This type of workout is very strenuous. If you haven’t exercised before, build some strength and fitness before attempting it or any other HIIT workout.

Table of Contents

HIIT and Weight Training Overview & Precautions

HIIT and weight training each provide a fast means of developing muscle tone, strength, and endurance. They also burn calories and body fat and provide cardiovascular benefits. HIIT comes with the added advantage of increasing our body’s HGH (Human Growth Hormone) level. This hormone is said to burn body fat, stimulate muscle development and substantially slow down visible signs of aging.

HIIT and weight training can be individually taxing, so it’s important not to overdo it. Your body and muscles need time to recover between sessions when doing either form of exercise. When doing both together, it’s even more vital to be conservative. Adding extra time to your workouts, or additional sessions, won’t bring about faster results.

Do too much, and it’s almost certain you will injure yourself and have to give up exercising until you recover. Aim for a maximum of three combined HIIT and weight training sessions per week.

HIIT and Weight Training Dietary Precautions

When doing either HIIT or weight training, it is important to follow a healthy diet. When doing both simultaneously, it is imperative.

Two macronutrients you must never skimp on when doing HIIT and weight training are protein and carbohydrates. Protein is essential for muscle development, while carbs are needed to restore glycogen (the muscle’s primary energy source), as the latter will be depleted during workouts.

Fiber and fats are also necessary to help keep energy levels up, so be sure to take in enough fruit, veggies, nuts, and whole grains. Drink plenty of water to stay hydrated.

HIIT and Weight Training Workout

How to Start Combining HIIT and Weight Training

Creating a routine that combines HIIT and weight training isn’t difficult. Follow the six easy steps outlined below, and you can quickly be up and underway.

1. Select Your Equipment

With HIIT, you only get a very short rest between exercises, so there will be no time for you to switch from dumbbells to kettlebells or a barbell. Choose which of these you want to work with, and stick with it for the entire session.

2. Use Light Weights

HIIT and weight training workouts involve many reps. To lower the risk of injury, use light weights, especially when

starting out. If you’re a woman who hasn’t been exercising for long, start with 2lb or 3lb weights. If you are reasonably fit, you may be able to start with 5lb weights. Males will usually be able to use heavier weights.

The idea is to use a weight that challenges you, but not to the point that you can’t complete your workout, or you have to resort to using poor form to do so. As your strength and fitness improve, you can progress to using heavier weights.

3. Decide Which Muscle Groups to Target

HIIT and weight training can be used to target a single muscle group, for example, your chest or core. It can also be used to target multiple muscle groups, such as the triceps and biceps, or upper back and shoulders. It can also give you a total body workout.

You will, of course, need to do different exercises to target different body areas. The time you spend working out will be shorter if you are targeting just one muscle group, as opposed to working two muscle groups or your entire body.

4. Decide Upon the Length of Your Workout

HIIT workouts typically run anywhere from 5 minutes to 30 minutes. It’s preferable to start with short workouts, building up to longer ones over time.

If you only want to target one or two muscle groups, you will get a good workout in 5 minutes. For a total-body workout, plan on spending 20 to 30 minutes exercising. However, with HIIT and weight training being such an effective combination, short workouts can be as efficient as long sessions of many other types of exercise.

5. Choose Your Exercises

When choosing your exercises, select those that target the muscle group or groups you want to strengthen and tone. Working on the basis that each exercise will take around 30 seconds to complete, factor this in when deciding how many

exercises to include in your session. If you plan on working out for 5 minutes, you will be able to select ten different exercises at the most.

6. Decide on an Intensity Ratio

The standard intensity ratio for many HIIT workouts, including the type covered in this article, is to alternate between high-intensity weight lifting and rest at a ratio of 2:1. An example is 20 seconds of high-intensity weight lifting, followed by a 10-second rest. This cycle would be repeated for the duration of the workout.

If you are just starting out and you find the 2:1 ratio too strenuous, try a ratio of 1:1 or even 1:2. In other words, 20 seconds working at high intensity, followed by 20 seconds working at low intensity. Or 15 seconds working at high intensity, followed by 30 seconds working at low intensity.

Tying it all Together

After completing the six steps above, you will be ready to do your first HIIT and weight training workout.

Before you begin, set a timer to alert you when it’s time to rest. Next, grab your weights, kettlebell or barbell and go through the exercises one by one, until you complete your workout.

HIIT and Weight Training Summary

By adding HIIT and weight training workouts to your existing exercise regimen, you will be able to enjoy a range of health and fitness benefits including muscle building and strengthening, increased stamina, a reduction of body fat and cardio conditioning. You will also be able to experience the anti-aging properties of HGH.

These benefits and more can be yours, all by doing 1 to 3 workouts per week that are never boring and don’t take long to do.

For more information on HIIT, read What is a HIIT Cardio Workout?

A 30-Minute Functional HIIT Circuit Anyone Can Try

How To Warm Up For This Workout

If you’re going to get the most out of a HIIT workout, you need to be firing on all cylinders from the start, and that means doing a proper warm-up beforehand. Now, you might well be doing HIIT because you’re short on time to exercise, but trust us when we say that a worthwhile warm-up need only take a few minutes.

The key to a good warm-up is thinking about the specific muscles you’re about to use and focusing on getting those muscles ready to go. Ahead of this HIIT workout you’ll want to start with some dynamic stretches – here’s a great seven-move warm up routine to use – and then go into a few exercise-specific warm-ups. The simplest way to do this is to run through a round of the exercises from the workout you’re about to do, completing just a few reps rather than working flat-out to time, and reducing the weight you’d use for any move that calls for a kettlebell or dumbbell.

Once you’ve done that, you’ll be able to hit your first circuit proper at full speed safely. If that means your workout is 40 rather than 30 minutes, that’s a fair trade-off. And if you really do only have 30 minutes max, then it’s usually smarter to shorten the workout than to skip the warm-up.

Functional HIIT Workout

The circuit involves nine functional exercises, most of which are bodyweight exercises, although you will also need a kettlebell and a pair of dumbbells.

For each exercise complete as many reps as you can within 35 seconds, then rest for 25 seconds before moving on to the next exercise.

Complete three rounds of the circuit. If you’re not sure how to do any of the moves click the header for a full explanation, and make sure to bear in mind the dos and don’ts from the F45 coaches.

1. Kettlebell swing

Do: Initiate the move with the hips, not the arms
Don’t: Swing higher than eye level

2. Burpee

Do: Raise your hands above your head when you jump
Do: Consider skipping the press-up at the bottom of the move, it’s optional

3. Bear crawl

Do: Keep your knees close to the floor to engage your core
Don’t: Let your back arch

4. High knees

Do: Keep knees high and tempo fast
Don’t: Dip your head and hunch your shoulders

5. Press-up

Don’t: Flare your elbows – keep them tucked in
Don’t: Let your hips dip – keep your core engaged

6. Star jumps

Do: Bend your knees to land softly

7. Dumbbell overhead press

Do: Bring the dumbbells all the way to your shoulders and push then above your head
Don’t: Curve your back as you extend the dumbbell

8. Bodyweight squat

Do: Get as low as you can
Don’t: Round your back or look down

9. Bicycle crunch

Do: Keep your shoulders off the floor

F45 offers high-intensity, 45-minute, circuit-based group training sessions. Visit

Circuit Training Insanity: 3 Hardcore Workouts to Burn Body Fat

If you’re looking to shave some points off your body fat percentage, circuit training workouts are about to become your new best friend. These whole-body workouts combine strength and cardiovascular training into one killer muscle-building, fat-burning session.

The secret is in cutting out rest. While most strength training workouts advise (and wisely so) rest between sets, circuit training workouts are built to cut out downtime. Targeting different muscles, one after the other, enables you to rest the muscle you just worked without resting the whole body. As a result, you’ll get all the strength building benefit plus an infusion of cardio and endurance. Mixing resistance training with a cardiovascular workout in this way has been shown to increase your metabolism. You’ll burn fat while you build muscle, shaving off body fat percentage points as you go.

Circuit training is also incredibly efficient. You’ll be amazed at how quickly you can get an effective full body workout while working through these circuits. Of course, achieving that efficiency means you’re cramming a lot of hard work into a short amount of time. You may find yourself having to go into beast mode to make it through these workouts. Moving continuously without rest demands major mental endurance, focus, and discipline – all of which you’ll build as you train.

There are three major types of circuit training workouts. The first two are similar, and in some cases interchangeable, but have some small differing advantages. Read below to find out more and see which is most appropriate to your goals. We’ve also included a sample bodyweight training circuit for each. These are fairly advanced, hardcore workouts. If you can’t do an exercise included with good form, simply substitute in something accessible to you that works the same muscles.

Before the first two (MRT and HIIT), be sure to warm up with light exercises and mobility drills to gently increase your heart rate and keep the joints safe. As Finisher circuits are designed for the end of a workout, you won’t need to warm up first.

1. Metabolic Resistance Training (MRT)

If your focus is on building strength, MRT is the way to go. MRT circuits consist of a series of four to eight exercises, usually multi-joint in nature, with little-to-no rest between sets. Built to up the metabolic output of exercise, these workouts fire up your body’s circuits, leaving them revving long after your post-gym shower. The effect is shockingly rapid results, maximizing your body’s “change capacity” for improvements of 50% in just 6 weeks.

This works on three levels: First, basic energy expenditure. A MRT workout’s burn can easily approach, or even surpass, 600 calories. Secondly, MRT massively increases excess post-exercise oxygen consumption, which is a fancy way of saying afterburn. This is the energy it takes to return to status quo post-workout. An MRT workout can up this energy consumption for over 38 hours. Thirdly, MRT counteracts the negative effects of lactic acid, building intense endurance that can lead to massive muscle growth.

Madman MRT Circuit:

Move through the sequence, resting 30 seconds or less between exercises. Rest 60 seconds or less after the last exercise, and then begin the sequence again. Try to move through the entire sequence three times. As your endurance grows, reduce the amount of rest, until you’re taking no rest between exercises and 30 seconds or less between circuits. Remember: if you can’t yet do any of these exercises with good form, replace it with something similar (regular squats for one-legged squats, for example), adding in the more advanced exercises as strength grows.

2. High Intensity Interval Training (HIIT)

HIIT workouts alternate between high intensity and low-to-moderate intensity intervals as the circuit progresses. If you’re looking to burn fat while building endurance, you’ll want to work some HIIT workouts into you plan. Like MRT, HIIT does crazy things for your EPOC, keeping your metabolism going strong long after you’ve left the gym. Because they work at such a high level of intensity, HIIT workouts also up levels of muscle-building hormones. This killer combination means you’ll gain muscle mass while burning off body fat. As an added bonus, you’ll get your heart rate way up, powering up your cardiovascular endurance.

Hardcore HIIT Circuit:

Move through the four exercises without rest in between. When you finish the circuit, take 30 to 60 seconds of rest, then repeat. Aim for three to five circuits. For the AMRAP (As Many Reps As Possible) intervals, you can increase intensity over time both by squeezing in more reps and lengthening the interval. You can also lengthen the static holds as strength grows. Be careful to maintain good form, even when trying to squeeze in more reps. Doing more reps won’t do you any good if you’re not doing them with integrity.

  1. Squat thrusts, 60 seconds, AMRAP
  2. Static squat, hold 60 seconds
  3. X-Pushup, 60 seconds, AMRAP
  4. Missing Arm Hold, hold 30 seconds each side
  5. V Up Exercise, 30 seconds, AMRAP
  6. Frozen V Sit Exercise, hold 30 seconds

3. Finishers

Finishers are for those days you need a little something extra. They’re quick, dynamic workouts you can add to the end of your normal routine. The goal is to finish your workout having given literally everything you’ve got. After a good finisher, you shouldn’t feel like working out any more for the day.

Finishers are extremely versatile. You can plan one in at the end of a workout for a little extra fat-burning power. You can also spontaneously add one in on days when you’ve got some extra energy left to burn. They’re also great for evening out a workout. If you’re wondering whether you’ll be able to climb stairs after a leg workout, but your chest feels like you could lift cars, you could restore equilibrium with an all-out, no-holds-barred chest-focused finisher.

The Total Exhaustion Circuit

This one is the definition of a “finisher,” built to squeeze out every last drip left behind from the day’s workout. It’s designed for strong bodies. If you’re a beginner, you can cut down on sets, and work you’re way up to the full four minutes per exercise.

It’s simple: Tabata push-ups + 60 seconds rest + Tabata squats.

(Tabata method is 20 seconds of all-out exercise, followed by 10 seconds of rest, repeated eight times. This adds up to four minutes per exercise, meaning this Tabata-style finisher will leave you wiped-out in 9 minutes flat.)

Todd Kuslikis is the founder of, a bodyweight exercise site that helps people build muscle and strength using only bodyweight exercises. He has created many bodyweight based training routines including his most popular 3 Month Bodweight Training Plan.

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Strength Training VS HIIT

When you engage in a healthy lifestyle, there are certain goals you will find yourself setting. Milestones to celebrate all the hard work you plan to put in. One key component a program that gets you results is having the proper elements working together. Strictly lifting weights and not doing cardio, may get you decent\xC2\xA0results, but you will be neglecting your cardiovascular health. On the flip side, doing cardio alone may burn fat temporarily, but it does nothing to alter the composition of your body concerning lean mass and fat mass.

Strength training is a great way to change body composition permanently, which leads to a whole host of health benefits. It serves as the number one way to add muscle mass to your frame, which in turn boosts your metabolic rate. A popular myth is that 1 lb. of muscle weighs less than 1 lb. of fat…not true. One pound of fat\xC2\xA0weighs the same as one pound of mass. What differentiates one from the other is that one pound of muscle is much more compact. Therefore it takes up much less space than one pound of fat. As a result, the more muscle mass you have, the tighter and more toned you appear.

Cardio Sessions Don’t Have to Be Long

As far as cardio is concerned, many people tend to think that long, drawn-out sessions are critical. The truth is, once the body hits a certain amount of time during a cardio session, doing more does more harm than good. Secondly, most people just don’t have the time to slave away on a machine, and could instead better utilize that time to get a lift in. One of the most efficient and time-saving forms of cardio is something referred to as HIIT, high-intensity interval training.

HIIT training involves all-out effort, often in the form of sprints, for up to 30 seconds. This type of training is considered anaerobic (takes place in the absence of oxygen), unlike other low to moderate intensity exercise, which is considered aerobic. Why does this matter? In the anaerobic state, our body can still build muscle. So even though an HIIT session is seen as cardio, you can still build muscle from it as a result.

Afterburn: Fire Up Your Metabolic Furnace

One of the huge perks of HIIT training is something referred to as the afterburn. The Afterburn is the period in which your metabolism experiences a boost, therefore turning your body into a furnace. The afterburn can last up to a whole 24 hours after an HIIT workout. Typical cardio burns calories during the cardio session itself, but once the session ends, so does the calorie burn. This is not ideal for long-term sustainability and reaching weight/fat loss goals.

Ideally, combining both\xC2\xA0strength training and HIIT will yield remarkable results. Why? Strength training alone will add muscle and lead to a tighter, stronger appearing physique. It will not work the cardiovascular aspect of a well-rounded fitness program. Doing cardio, specifically HIIT, will accelerate body fat loss at a faster rate than if you were to do strength training alone.

So how can you make the two work together to reach your goals quicker and in better condition than anticipated? The key is to ensure the elements of your strength training program include hitting all muscle groups throughout your workout rotation. Also, throw in 2 HIIT workouts per every 7-day workout cycle. Some examples of HIIT workouts can include airbike sessions, sled pushes, kettlebell swings, or total-body workouts that consist of bodyweight exercises done intensely (think Tabata-style).

The Key is Finding Balance

No matter your fitness or physique related goal, finding the right combination of cardio and resistance training, along with a proper, health-based nutrition regimen, you can reach your goals sooner than expected. Take advantage of what both strength training and HIIT offer to get the most out of your time and workout routine.

Bring Your Training Home

Having a home gym can save you a lot of time and money, while also avoiding lineups for equipment and allowing you to create your own “judgment free” zone. And it does not have to be expensive. Our exclusive Blitz Air Bike is the perfect piece of equipment to start or augment your HIIT program, and it’s less than $700 CAD. And check out our garage gym builder for big discounts getting the exact weightlifting setup you need!

HIIT is changing the way we work out, here’s the science why it works

Few forms of exercise have been as highly and intensely researched – or publicised – in recent years as high-intensity interval training (HIIT). In 2018, HIIT headed up the yearly survey of worldwide fitness trends by the American College of Sports Medicine (ACSM). It has remained in the top five since it entered at the top spot in 2014. HIIT is proving to be an enduring hit.


True, HIIT is down to number three in the ACSM’s 2019 chart, behind wearable tech (number one) and group training (number two). But if you’ve been to a fitness class lately, then there’s a strong chance that you did HIIT, even if you didn’t realise it at the time. “The best way to explain it is repeated bouts of high intensity followed by a bout of recovery,” says Tom Cowan, an exercise physiologist at the Centre for Human Health and Performance (CHHP) on London’s Harley Street.

What is HIIT and what does it do?

According to the ACSM, high-intensity intervals are exercises that you typically perform at 80 to 95 per cent of your maximum heart rate, for anywhere from five seconds to eight minutes. Generally, the shorter the interval, the higher the intensity and vice versa. The work intervals are alternated with periods of complete rest or active recovery performed at 40 to 50 per cent of your maximum heart rate, lasting for the same duration (although they can be longer or even shorter depending on your fitness).

HIIT is highly adaptable for varying fitness levels and goals, which partly explains its popularity among everybody from elite athletes to cardiac rehab patients. It can be performed on gym equipment such as static bikes, treadmills and rowing machines (cardio HIIT), or via exercises such as press-ups (bodyweight HIIT).

Its popularity is welcome news, because HIIT has been shown to improve fitness, cardiovascular health, cholesterol profiles and insulin sensitivity, which helps stabilise blood glucose or sugar levels – of particular significance to diabetics. HIIT also reduces fat – both abdominal and the deep, visceral kind that engulfs your inner organs – while maintaining muscle mass or, in less active individuals, increasing it.

HIIT is said to improve the function of the mitochondria in your cells (the orange cross-section in this illustration), so they get better at converting oxygen and nutrients into fuel for your muscles © Getty Images

More strikingly, according to a small study in Cell Metabolism in 2017, HIIT effectively halts ageing at the cellular level, by increasing the production of proteins for the mitochondria, your cells’ energy-releasing powerhouses, which otherwise deteriorates over the years. Other forms of exercise such as strength training do likewise, but HIIT is more effective. The study also stated that muscle cells, like those in the brain and heart, wear out and aren’t easily replaced, so if exercise prevents deterioration of mitochondria in muscle cells, or even restores them, then it likely does so in other tissues too.

Similarly, HIIT beats continuous moderate-intensity exercise when it comes to releasing brain-derived neurotrophic factor (BDNF), a protein that protects nerve cells. This promotes plasticity (the forming of new connections, which aids learning and memory) and may even help regulate eating, drinking and body weight.

Perhaps HIIT’s biggest selling point is its efficiency: a workout can last up to an hour, but it can also be completed in 20 minutes or less. Tabata, one of the most well-known HIIT protocols, consists of 20 seconds of work followed by 10 seconds of rest, repeated eight times for a total of just four minutes, not counting the warm-up and cool-down.

Dr Izumi Tabata (in the lab coat) has lent his name to a HIIT protocol that produces greater improvements in fitness than longer bouts of moderate exercise

In a famous 1996 study by Tabata’s namesake Dr Izumi Tabata, people who performed the four-minute protocol on an exercise bike five times a week improved their VO2max – the uppermost rate at which your body can utilise oxygen for energy during exercise – by 15 per cent after six weeks. People who exercised for 60 minutes at moderate intensity five times a week only improved their VO2max by a mere 10 per cent. Moreover, the Tabata group boosted their anaerobic capacity – the body’s ability to produce energy without oxygen, used for short bursts of hard effort – by 28 per cent. The continuous exercise group’s stayed the same.

HIITing the spot

It sounds like the fanciful stuff of home shopping channel infomercials, but HIIT is legit – even The One-Minute Workout, a book published in 2017. The workout (three 20-second intervals interspersed with one to two minutes of recovery) improved the fitness of people who performed it three times a week for 12 weeks, just as much as those who did traditional cardio for 50 minutes three times a week. It was devised by Dr Martin Gibala of Canada’s McMaster University, who is one of the leading researchers into HIIT. “It’s not a fad,” confirms CHHP’s Cowan. “It’s completely got the backing, and there are more and more studies coming out.”

While it might seem like a recent trend, HIIT isn’t a new concept. It’s been employed for at least a century by athletes. For example, legendary Finnish distance runner Paavo Nurmi set a 1,500m world record in 1924 by running repeated hard sprints in training. What is new is the scientific research, which began in earnest at the start of this century.

Finnish middle-distance runner Paavo Nurmi (right) incorporated high-intensity interval training into his regime. He broke 22 world records and won nine Olympic gold medals during his career © Getty Images

HIIT has been heralded as a powerful weapon in the fight against unhealthy lifestyle-related diseases such as obesity and type 2 diabetes. And if nothing else, it’s convenient: one of the most-cited obstacles to physical activity is lack of time.

“Also, a lot of cool, fashionable gyms and studios that are all glammed-up with music – not just in London but there are plenty there – follow a HIIT-based approach, with circuit-type or spin classes,” says Cowan. “That’s quite appealing to a lot of people, as opposed to having to jog for an hour in the park, which is a bit more monotonous.”

This variety is what makes HIIT so impactful. “Because you get the rest between , you can spend more time doing each one at a higher intensity, which you couldn’t sustain otherwise,” says Cowan. “If you do 10 two-minute work intervals, you’ve actually managed 20 minutes.”

Ramping up the intensity forces your body to tap into its anaerobic system for energy, because it can’t supply the oxygen required to work aerobically quickly enough; in the recovery intervals, your body reverts to its aerobic system. As the session goes on, your body relies less on the anaerobic system, because quick-release energy sources of phosphocreatine and glycogen (glucose stored in your muscles) become depleted. Your body will therefore start to rely more on the aerobic system, which releases energy more sustainably but slowly from fat. You won’t be able to achieve quite as high an intensity as you could at the start, but the upshot is a double whammy. “You’re essentially using a mixture of the anaerobic and aerobic systems, so you get an improvement in both,” says Cowan.

The release of brain-derived neurotrophic factor (BNDF), which protects nerve cells, is boosted by HIIT training © Alamy

Respiring anaerobically has knock-on effects. “It’s like when you’re puffing and panting after running for a bus, you’re trying to repay the oxygen deficit,” says Cowan. This excess post-exercise oxygen consumption, which is more pronounced with HIIT than continuous exercise, burns a further 6 to 15 per cent more calories as your body replenishes itself.

Lactic acid and hydrogen ions produced during anaerobic respiration have to be cleared, as do hormones such as adrenaline; your body temperature and heart rate also need bringing back down: “All of those things increase the workload following the exercise.” Workload is one of the reasons why we’re not all doing HIIT all the time: you have to recover adequately between sessions. “Three sessions a week is probably okay but it’s not something that you’re recommended to do every day,” says Cowan.

If you don’t sufficiently replenish your glycogen after HIIT with quality carbohydrate sources, you won’t be able to achieve a high-enough intensity in subsequent sessions. “And, actually, diet in combination with exercise is what’s really going to help with fat loss,” says Cowan. “It’s no good training like this and eating rubbish.” Bodyweight HIIT meanwhile will, like other forms of resistance training, cause micro-tears in your muscle that need time and protein intake to repair. Research recommends 60g of carbs with between 10g and 20g of protein post-exercise to optimise glycogen synthesis.

HIIT’s risks

You can have too much of a good thing, though especially if you’re a beginner and don’t have a qualified professional on hand to ensure that the intensity isn’t too high for you. A study in the Federation Of American Societies For Experimental Biology Journal showed that interval training can actually halve the function of mitochondria in newcomers. And just one overzealous spin class can be enough to trigger rhabdomyolysis, where muscle fibres break down and leak into the bloodstream, which can in turn lead to kidney failure.

There is growing evidence that repeated, short bouts of intensive exercise is better at burning off the fat that sits around your abdomen and internal organs than longer, more sustained bouts of exercise © Alamy

HIIT is considered safe for most if correctly prescribed, although it may raise coronary risk for sedentary people. But Cowan stresses that you should consult a doctor if you’re new to exercise or have any kind of clinical diagnosis. He also recommends starting off with six weeks of continuous, lower-intensity training before transitioning to sessions of three to four moderate-intensity reps.

Even when you can manage sessions of six to 10 reps at high intensity, you should offset them with continuous lower-intensity sessions, plus strength training to maintain muscle. Penn State University advocates no more than 30 to 40 minutes a week above 90 per cent of your maximum heart rate to prevent injury, weakness, tiredness, illness, disrupted sleep and low mood.

Another risk with HIIT is that it’s perceived as an easy option when it’s not. “You’ve really got to push yourself,” says Cowan. “It’s not that enjoyable for some people.” That said, HIIT has been rated in some studies as more enjoyable than continuous vigorous and even moderate-intensity exercise. That might be because it’s less mind-numbing, but the University of Turku, Finland, also determined that HIIT releases more painkilling endorphins in the brain. This negates the negative feelings and enhances motivation more than continuous moderate-intensity exercise.

Finally, while short workouts sound enticing, and remove the excuse of lack of time, they may give the impression that only a little exercise is necessary when most people should be getting more, not less. As the ACSM admits: “Meeting the goal of 75 minutes of vigorous activity per week may prove challenging through HIIT alone.” Alternatively, the ACSM recommends 150 minutes of moderate-intensity exercise per week spread over five days, or a combination of the two. HIIT gets the arduous exercise out of the way quickly, not so you can put your feet up, but so you can enjoy more activities that feel less like hard work.

This is an extract from issue 331 of BBC Focus magazine.

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