High Intensity Interval Training is clearly highly effective for conditioning and fat loss. However, like all exercise stimulus overdoing it can make people more prone to injury and overtraining.
A new study presented by Penn State Associate Professor Jinger Gottschall at the recent ACSM conference provides some specific clues as to how much HIIT is too much. The research presented showed that the best results are obtained by spending 30 – 40 minutes of total time per week with the heart rate above 90% of maximum heart. More time at this intensity makes participants more prone to injury.
All exercise acts as a stressor and as with all stressors to much stress to soon does not allow the body to recover and adapt from the stress and will always result in injury or illness.
Advanced exercisers may be able to tolerate short periods where they can use more time at 90% of their maximum heart rate, but for the majority of exercisers it would be wise to stay under 40 Total Minutes of HIIT Training with heart rate above 90% of Maximum.
This highlights the potential advantages of Coaches encouraging the use of chest strap heart rate monitors with one on one PT clients. These monitors can be purchased from many sources. To understand the three different methods of managing a client's work/rest ratio using a heart rate monitor read this previouis blogpost: http://workoutanytime.blogspot.com/2018/02/managing-workrest-ratio-in-hiit-training.html