How much HIIT is too much?
First off, happy Halloween to all! Enjoy the candy, wine, or whatever you will partake in this evening/weekend! Remember it is important to let loose a little (in moderation) in order to maintain a healthy lifestyle.
As a trainer I pride myself on the fact that I'm continuously checking out and try different gyms in my area and see what types of fitness classes that they offer. From what I've noticed most of them seem to be putting their own spin on High Intensity Interval Training or HIIT for short. HIIT has become increasingly popular over the past 10-20 years.
HIIT training originated with Sprint interval training which involves short periods of anaerobic exercise followed by recovery periods. The high intensity period should be at near maximal intensity with recovery periods usually at a 1:1 work to rest ratio. Often times when intensity is at a max, a longer rest period is required.
One of the most well known styles of HIIT is TABATA TRAINING. Professor Izumi Tabata performed a study in which participants used 20 seconds of ultra-intense exercise followed by 10 seconds of rest, repeated continuously for 4 minutes (8 cycles). The exercise was performed on a mechanically braked cycle ergometer. This 4 minute workout was repeated 4x/week for 6 weeks and it was found that they had aerobic and anaerobic gains greater than those subjects who performed just steady state cardio during the same time period. One thing to not here is that participants who were not able to maintain a steady high intensity pace on the ergometer were disqualified from the study. If you've done the math here that's only 16 MINUTES of exercise/week.
So is HIIT training meant to be done daily? How much is too much?
What we first have to do is to understand if the workouts you are even doing even qualify as HIIT. If you are truly working at a high intensity, it should be nearly impossible to speak or to maintain output for more than a minute or two. Most experts recommend capping your HIIT sessions to one to two 30-minute classes/week (keep in mind that during this 30 minutes only 10-15 should be spent in max heart rate zone 85% or more). Jinger Gottschall, a PHD and professor of Kinesiology at Penn State University collected data of hundreds of HIIT participants and found that those taking part in a high volume of HIIT showed symptoms of overtraining and were injured more often than those who performed a lower volume. "I was surprised by the obvious difference between doing 30 to 40 minutes (of HIIT) and doing more than 45 minutes," Gotschall says. "The difference in performance, stress-related feelings, and sleep quality was significant." Another major effect that too much high intensity training can have on the body is an immediate increase in cortisol, a hormone that is released when the body is under stress. Chronically high levels of cortisol can increase your risk for a variety of health issues, such as sleep disturbances, digestive issues, weight gain, and memory impairment. Excess cortisol also encourages fat gain, particularly in the abdomen.
So what should we do?
Once again experts recommend capping high intensity sessions to once or twice a week at no more than about 30 minutes/session. When your not HIITing it, focus on strength training, yoga or mobility work, or perform some low intensity cardio work. Finding a good balance is ideal for optimal health and longevity.