HIIT (High Intensity Interval Training) has increased in popularity in the last decade as the benefits of HIIT become widely known and it takes less time to complete than more traditional steady state cardio sessions.

Swapping a 60-minute cardio session to one that is a third in length, whilst helping to preserve lean muscle mass and burn body fat? Sign us up!

Reasons for HIIT

The higher the exercise intensity the greater the metabolic impact which is ideal when body composition changes and reduction in body fat is the goal. A 2008 study showed that high intensity-exercises over 6 weeks at 3 sessions per week, were beneficial to increase the body’s ability to burn fat along side cardiovascular improvements.

Steady State Cardio VS HIIT – Excess Post-Exercise Oxygen Consumption Benefit

HIIT also produces Excess Post-Exercise Oxygen Consumption (EPOC). EPOC is the metabolic rate’s recovery back to pre-exercise levels. It also used within the body to:

  • Produce ATP (energy) to replace the ATP used during the workout
  • Resynthesis of muscle glycogen from lactate
  • Restore oxygen levels within the body
  • Aid in the repair of muscle tissue damaged tissue during the workout
  • Restore body temperature to resting levels

Your metabolism will increase during training whether you are performing a

strength session or a cardio one. Post cardio training, your EPOC returns to normal after approximately 12 hours. Post strength training is takes your EPOC nearly 72 hours to return to normal resulting in more energy expended over all.

As the relationship between HIIT and EPOC is further researched, the EPOC levels between steady state cardio and HIITT shows similar impact post training. This is worthy of noting as a HIIT session can be performed in a far shorter time period than a continuous state session. In fact studies are showing that 20 minutes total of HIIT is equivalent to 50-60minutes of stead state cardio for EPOC.

However the correct level of training intensity must be achieved during these HIIT sessions. The intensity is, of course relative, to the person performing the HIIT session.

Work vs Rest Intervals

HIIT session should ideally be between 10-20minutes and extending the session longer generally means that a high enough intensity of training isn’t being met during the work intervals.

Work intervals should be between 10-30 seconds with longer rest intervals to allow for ATP (energy stores) to replenish. The work intervals create the metabolic demand and use the anaerobic energy system whilst the rest periods allow you to recover and use the aerobic energy system.

When working at near maximal capacity (85-95% Vo2max) the body also increases growth hormone, testosterone, cortisol, endorphins, noradrenaline and adrenaline which all impact body composition and anabolism.

Shorter work period allow for higher intensity output whilst longer work periods will decrease the overall output. When starting HIIT, focus on longer work intervals 30-45 seconds and decreasing in time as your fitness and anaerobic output levels increases.

Frequency

More is not more in the case of HIIT training. Due to the impact this level of training has on the body, adequate rest and recovery must be incorporated. If body composition changes and fat loss is the goal, then we always encourage women to look to their nutrition and strength training first. Ensure you’re in a calorie deficit and have a structured strength program in place before incorporating HIIT.

Unsure where to start for your goals or how to incorporate HIIT into your training, get in touch

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References
  1. Zalesin KC, Franklin BA, Lillystone MA, et al. Differential loss of fat and lean mass in the morbidly obese after bariatric surgery. Metab Syndr Relat Disord. 2010;8(1):15-20. doi:10.1089/ met.2009.0012.
  2. Perry, Christopher G.R.; Heigenhauser, et al. (December 2008). “High-intensity aerobic interval training increases fat and carbohydrate metabolic capacities in human skeletal muscle”. Applied Physiology, Nutrition, and Metabolism 33 (6): 1112-1123.
  3. Helgerud, J., et al. 2007. Aerobic high-intensity intervals improve VO2max more than moderate training. Med Sci Sports Exerc, 39 (4), 665-71.
  4. Wisløff U, et al. High-intensity interval training to maximize cardiac benefits of exercise training? Exerc Sport Sci Rev. 2009 Jul;37(3):139-46.4
  5. Tom J. Hazell, T. Dylan Olver, Craig D. Hamilton, and Peter W.R. Lemon. “Two minutes of sprint-interval exercise elicits 24-hr oxygen consumption similar to that of 30 min of continuous endurance exercise.” International Journal of Sport Nutrition and Exercise Metabolism22, no. 4 (2012): 276-283.
  6. Lauren E. Skelly, Patricia C. Andrews, Jenna B. Gillen, Brian J. Martin, Michael E. Percival, and Martin J. Gibala. “High-intensity interval exercise induces 24-h energy expenditure similar to traditional endurance exercise despite reduced time commitment.” Applied Physiology, Nutrition, and Metabolism39, no. 7(2014): 1-4.
  7. Cameron B. Williams, Jason G.E. Zelt, Laura N. Castellani, Jonathan P. Little, Mary E. Jung, David C. Wright, Michael E. Tschakovsky, and Brendon J. Gurd. “Changes in mechanisms proposed to mediate fat loss following an acute bout of high-intensity interval and endurance exercise.” Applied Physiology, Nutrition, and Metabolism 38, no. 12(2013): 1–9.