PT on the Net Research

HIIT Regular to Ripped: The New Fat Burning Zone


Learning Objectives

  1. Describe how there is more to high intensity interval training than the Tabata training protocol.
  2. List the benefits of high intensity interval training compared to medium intensity continuous training for reducing body fat in various populations of subjects in research studies.
  3. Write training programs for clients based on the protocols used in the research studies.

Many fitness professionals think high intensity interval training (HIIT) is a relatively new method of training, when in fact it’s first documented use was in 1912.  High intensity interval training certainly has come into the mainstream of fitness in the past decade.  Ironically, perhaps the most famous HIIT training program is “Tabata.”  Izumi Tabata (1996) and his colleagues conducted their research based on the request of the coach of the Japanese speed skating team.  The coach wanted to know if there was a training method that can be used for his skaters that decreased volume, but maintained aerobic and anaerobic capacity, skating speed, and winning medals.  Tabata discovered his four-minute high intensity interval training program not only maintained aerobic and anaerobic capacity, it improved them both.  This finding was exciting to Tabata and the coach, not to mention the skaters.

Yet, the actual research done by Izumi Tabata (1996) has limited use in a group exercise class or Boot Camp.  This is because the Tabata work-out has people training at 100% of their maximal capacity.  In terms of using a Tabata work-out for fat reduction, Izumi Tabata not only did not calculate fat loss, he did not calculate calories burned during his work-out.  Not to worry however, many other researchers have done HIIT and medium intensity interval (MIIT) training programs where they calculated total calories burned as well as many calculations to determine fat loss.  

More Then Tabata

One of the most interesting studies that gets little or no recognition was done by Tremblay, Simoneau, and Bouchard (1994).  They compared medium intensity continuous training (MICT) & medium intensity interval training (MIIT) on fat loss and muscle metabolism.  The MICT group did 20 weeks of endurance training on a cycle ergometer, four - five times/week, for 30 to 45 minutes, at an intensity of 60% - 85% of heart rate reserve.  The MIIT group did 15 weeks of training which consisted of 25, 30-minute aerobic training sessions at 70% of maximal heart rate reserve plus 19 short interval sessions (10 – 15 work bouts, duration of 15 – 30 seconds) and 16 long intervals (4 – 5 work bouts, duration of 60 - 90 seconds).  The intensity of the interval training was 60% - 70% of maximal work output.  Recovery was when the heart rate lowered to 120-130 beats per minute.  The results indicate the total calories burned for the endurance group for the entire study was 28,757.04 and the MIIT group burned 13,829.17, a difference of 14,927.87.  The remarkable finding in this study was that the MIIT group decreased their sum of six skinfolds nine times less than the endurance group.  The MIIT group also had a significant increase in enzymes promoting fat being used as energy for muscle contraction.  The important conclusion about this study is that most clients will embrace an interval training intensity of 60 – 70% of their maximum effort.

Jumping ahead 18 years, Heydari, Freund, and Boutcher (2012) conducted a study on the effect of high intensity interval exercise (HIIE) on fat reduction on young overweight males.  They measured the following variables:  total body fat, abdominal fat, trunk fat, visceral fat mass, and fat free mass.  There was a HIIE and a control group.  The HIIE group did 8-seconds of exercise at 80 – 90% of peak heart rate at a cadence between 120 and 130 rpm on a cycle ergometer, followed by 12-seconds of recovery at 40 rpm.  They performed this work-to-rest ratio for 20-minutes, three times/week for 12 weeks.

The results for the HIIE group are remarkable considering there was actual work of 8-minutes per work-out, and 24-minutes per week.  These are the results for the HIIE group:  aerobic power improved 15%, weight loss = 3.3 pounds, total fat mass decreased by 4.4 pounds, abdominal fat decreased by 0.22 pounds, trunk fat decreased by 3.3 pounds, visceral fat decreased by 17%, waist circumference decreased by week six 3.5 cm, fat free mass increased 0.88 pounds for the legs, and fat free mass increased 1.5 pounds for the trunk.  The researchers conclude that exercise prescriptions with minimal work, but producing fat reduction are the key to improving exercise compliance.

Trapp, et al., (2008) investigated the effect of a 15-week high-intensity intermittent exercise (HIIE) program on subcutaneous and trunk fat and insulin resistance.  Forty-five women with mean BMI of 23.2 and average age of 20.2 years were in the study.  Subjects were randomly assigned to one of three groups: HIIE (n=15), steady-state exercise (SSE; n=15) or control (CONT; n=15).

For the HIIE protocol, each subject performed 8-seconds of cycle sprinting and 12-seconds of active recovery pedaling 20 and 30 rpm for a maximum of 60 repeats a session.  At the beginning of the 15-week training period, HIIE subjects started with a lower pedal resistance and worked at their maximum when sprinting.   In the steady state group, the subjects did a 5-min warm-up at a comfortable workload after which they exercised at 60% VO2peak.  Subjects started the 15-week program exercising for 10–20 minutes. The duration of the exercise was gradually increased to a maximum of 40 minutes per session. When subject's fitness improved, the resistance was increased by 0.5 kg increments.  The results show that both groups improved their cardiovascular fitness.  Only the HIIE group had a significant reduction in total body mass, fat mass, trunk fat, and fasting plasma insulin levels.

Zhang, et al., (2017) compared the effect of moderate-intensity continuous training (MICT) and high-intensity interval training (HIIT) on reducing abdominal visceral fat in obese young women.  Forty-three participants did either HIIT (n = 15), MICT (n = 15), or no training (CON, n = 13) for 12 weeks.

The abdominal visceral fat area (AVFA) and abdominal subcutaneous fat area (ASFA) of the participants were measured through computed tomography scans pre-and post training. Total fat mass and the fat mass of the android, gynoid, and trunk regions were assessed with dual-energy X-ray absorptiometry.

MICT group participants did continuous exercise on a cycle ergometer at an intensity of 60% of V̇O2max until the targeted 300 kJ of work was achieved.  The pedal frequency was 60 rpm during each training session.  HIIT group participants repeated 4-minute cycling exercise bouts at an intensity of 90% of V̇O2max, followed by a 3-minute passive recovery until the targeted 300 kJ of work was achieved.

For the first four weeks, the participants in the two experimental groups exercised for 200 kJ (excluding warm-up and cool-down) for one session per day, 3 days per week.  During the fifth through twelfth weeks, the training frequency was increased to 4 days per week, and the total work done in each session was increased to 300 kJ in both groups.

 HIIT
 Weeks  1-4  5-8  9-12
 Exercise Time (min)  29.4  37.8  34.4 = 33.86 min/week
 Heart Rates  between 164-169 bpm

MICT
Weeks 1-4 5-8 9-12
Exercise Time (min) 51.2 74.4 62.6 = 62.73 min/week
Heart Rates between 164-169 bpm

The results show that the reduction in AVFA, ASFA and combined AVFA and ASFA were the same for both training groups.  Fat percentage, total fat mass, and fat mass of the android, gynoid, and trunk regions did not differ between HIIT and MICT.  The authors conclude that the obvious choice for reducing fat content is HIIT considering the same results were achieved in half the time.

Higgins, et al., (2016) investigated the effects of sprint interval training (cycling) (SIT) and moderate-intensity continuous cycle training (MICT), with equal estimated energy expenditure during training, on body composition and aerobic capacity.  The training lasted six weeks.  The subjects were previously inactive overweight/obese women (n = 52; age, 20.4 years).  Training was performed in a group-exercise format similar to cycling classes in commercial gyms, and included 3 sessions/week of 30-seconds "all-out" cycling sprints followed by 4 minutes of active recovery (2.5 - 3.5 minutes of near-maximal effort interspersed with 16-28 minutes of recovery), or continuous cycling for 20 – 30 minutes at 60%-70% heart rate reserve to expend a similar amount of energy duration of training.

Without significant changes in body mass, there were greater relative reductions in SIT than in MICT in total fat mass and android fat mass.  Aerobic capacity increased in both groups, but the relative increase was 2-fold greater in SIT.  The authors conclude that SIT cycling reduces fat mass and increases aerobic capacity more than continuous MICT cycling in overweight/obese young women.

Conclusions

Many researchers have investigated the effect of HIIT and MIIT on calories burned (during and after training), waist and hip circumferences, skin folds, total body fat, abdominal fat, trunk fat, visceral fat mass, fat mass of the android, gynoid, and trunk regions, and abdominal visceral and subcutaneous fat.  Researchers have also looked at the effect of HIIT on resting fat oxidation rate 24 hours post-work-out, fat free mass of the legs and trunk, and aerobic and anaerobic capacity.

Most studies show that HIIT, and one that used MIIT, causes an increase in fat burning and an increase in fat being used as energy during exercise, a reduction of fat percentage and fat mass, a decrease in skinfolds, and a decrease in waist and hip circumference.

References

Heydari, M., Freund, J., and Boutcher, S.H.,  (2012), The effect of high-intensity intermittent exercise on body composition of overweight young males, Journal of Obesity. 2012;2012:480467. doi: 10.1155/2012/480467.

Higgins, S., et al., (2016) Sprint interval and moderate-intensity cycling training differentially affect adiposity and aerobic capacity in overweight young-adult women.  Applied Physiology Nutrition and Metabolism. 41(11):1177-1183.

Tabata, I., et al., (1996).  Effects of moderate-intensity endurance and high-intensity intermittent training on anaerobic capacity and VO2max. Medicine and Science in Sports and Exercise, 28 (10): 1327–1330.

Trapp, E.G., et al., (2008) The effects of high-intensity intermittent exercise training on fat loss and fasting insulin levels of young women.  International Journal of Obesity, 32, 684–691.

Tremblay, Simoneau, and Bouchard (1994). Impact of Exercise Intensity on Body Fatness and Skeletal Muscle Metabolism. Metabolism 43(7): 814–818.

Zhang, H., et al., (2017) Comparable Effects of High-Intensity Interval Training and Prolonged Continuous Exercise Training on Abdominal Visceral Fat Reduction in Obese Young Women.  Journal of Diabetes Research. 2017;2017:5071740. doi: 10.1155/2017/5071740. Epub 2017 Jan 1.