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What’s Wrong with HIIT Training

high intensity interval training (HIIT) has exploded

Recently, high intensity interval training (HIIT) has exploded onto the fitness scene. Once an elite form of training reserved for athletic conditioning coaches and athletes, HIIT training is now being employed by personal trainers, boot camp instructors and fitness enthusiasts.

Whether you are a performance athlete, a long distance runner or looking to trim down, the adaptations and metabolic benefits of HIIT training are incredible- when  done correctly.  As with many special skills and techniques that become generally popularized, the parameters of the HIIT system of training that make it so useful, often become misused along the way.

HIIT training incorrectly

HIIT training done wrongHere are some of the ways HIIT training may be used incorrectly:

  • You may not be prepared for such high intensities. Have you ever gone to a new class… come home and not so sore you have not been able to walk for the next few days? After requiring assistance to reach the oatmeal from the cupboard and to get in and out of your car, you vowed never to set foot in that gym again. If you (or your trainer makes you) go too hard, too soon, before you are ready, you increase your risk of injury and may acquire a negative attitude towards HITT training.  Simply put, one must gradually work up to HIIT training. This is not to say HIIT training is not for you, rather just not now.
  • You are not training at HIGH enough intensities. The intensities at which many individuals perform intervals are generally enough to fatigue them, but not high enough to induce the desired benefits of HIIT training. The aim is to generate the “afterburn” effect, wherein the body’s metabolic rate is elevated for a longer duration following the exercise bout. To do this, intervals need to be at or above 8/10 on the modified Borg scale. This means that you are breathing very heavily and unable to speak.  HIIT training will result in greater calories burned throughout the day, for those desiring weight loss and physiological adaptations that enhance performance.When truly training at this intensity, the individual should NOT be able to sustain the interval for longer than 20-30 seconds.  The interval should be an extremely explosive burst, followed by a low intensity recovery period.
  • Not taking enough recovery time. Recovery is key. This refers equally to the intervals, as it does to the recovery days between exercise bouts. The body requires time to regenerate the tissues that were stressed during HIIT training. The body cannot tell the difference between external and internal stress, and will produce cortisol as a result. Cortisol production is extremely important in reducing inflammation and mobilizing fuel for the body. However, excessive production of cortisol impairs the body’s regenerative capabilities, leads to increased visceral fat storage and a compromised immune system. For this reason, training consistently at high intensities for long durations, can have adverse health effects, leading to overtraining and injury. To avoid this, the American Council on Exercise (ACE, 2014) has designed a three zone training model which indicates 10-20% of training volume should be at high intensities, with the remainder of time spent in low to moderate zones.

follow the principles… that what makes HIIT so effective!

When beginning any training program, it is important to consider what your goals are and the most appropriate way to achieve them.  As an ACSM certified personal trainer, I recommend you consult a certified personal trainer when starting out to ensure you achieve your goals safely and effectively.  If you decide that HIIT training is right for you ensure you get the most out of your training by following the principles that make it so effective.


American Council on Exercise Personal Trainer Manual.  American Council on Exercise, p.411, 2014.

Written By Sarah Lambert, Infofit Instructor,  ACSM CPT