Author: Graham Mitchell

Is your HIIT regimen breaking you down or building you up? There is a fine line between the two.

For those of you that may not be aware, HIIT is an acronym for high intensity interval training. Although this form of training has been around for decades, it has become a hot trend in the fitness world these days. Many articles have been written on what HIIT actually is as well as the different applications of it. At the end of the day, there is no perfect regimen. You can practice HIIT, low intensity interval training (LIIT) or NIIT (for those who chose to do no interval training at all). How do you know which is appropriate? Ask yourself, is the exercise program tailored to the goals, abilities, deficiencies, limitations and condition of those following it. Is it right for you? Is it right for your clients? All of them? Really? Let's see…


According to the National Library of Medicine, extreme overtraining or Rhabdomyolysis occurs when broken down muscle tissue leads to the release of muscle fiber into the bloodstream. This condition often results in kidney damage and/or failure. In case you haven't seen the recent HIIT trends out there, they usually consist of a conglomerate of explosive movements or plyos, mountain climbers, burpees, and so on. Let me be clear, I believe all of these are great exercise tools when applied properly. However, there are many issues with the one-size fits all approach to fitness, particularly when in the context of a high intensity routine with excessive ground contact.


(Lehmann M, et al. Autonomic imbalance hypothesis and OTS (overtraining syndrome). Med Sci Sports Exerc 1998;30: 1140.)


I have had the luxury of working with a wide range of clientele from professional athletes of almost every major sport, to recovering spinal injury patients. I have worked with some of the best coaches in the strength and conditioning field and in the private sector as well. Early on I learned a key factor in exercise prescription that changed everything for me. My mentor, Roy Holmes (head performance specialist at EXOS, the leading sports performance company in the country), opened my eyes to the idea that the thought process that goes into the workout is typically more valuable than the actual exercises themselves.


I am not suggesting that any old exercises will get the job done. That would be somewhat of a contradiction. Doing Olympic lifts (or any exercise for that matter), to exhaustion, far past what Michael Boyle (one of the top Strength and Conditioning coaches in the country) calls “technical failure", is clearly an exercise in futility. But if you have considered the: who, what, why, when, where, and how of your workout program, chances are what you put into it will be drastically different than if you simply focused on “the meat"…the where, when and what.

That brings us back to the topic of discussion. How do you know if you are performing or instituting a responsible, safe and effective HIIT workout or simply overtraining, ultimately decreasing overall performance and damaging joint health and function. It starts with “the who". Arguably the most effective way to “grade your limits" is to use the heart rate method. Although the typical 220-age method of estimating an individual's' maximum heart rate has been widely used, this type of age predicted max HR, may produce variations of plus or minus 10 bpm, which is unacceptably inaccurate (McArdle, W 473). Using the heart rate reserve method or “Karvonen formula", a person's resting heart rate is factored into the equation as well as the exercise intensity (percent of max HR) in order to determine their target HR, a far less arbitrary formula. However, there is a more detailed age based HR formula that can be used to estimate max HR for the sole purpose of applying it to the Karvonen formula and calculating the target HR zone.

Max HR = 206.9 – (0.67 x age)

Now, in order to determine exercise intensity (recovery HR), a good rule of thumb is to determine a person's current fitness level (low, moderate, high, very high). For low fitness levels, 50-65% of max HR is a safe place to begin. Moderate fitness levels can range between 66-77% and high to very high fitness levels can sometimes be pushed to 90% of the maximum HR. This figure represents the desired percent of the max HR.

Karvonen Formula: Target Hr = (Max HR – Resting HR) x % + RHR


By using the heart rate recovery style of training, the individuals involved in the training will get both an anaerobic and aerobic workout simultaneously. Once the target HR is reached, the rest portion of the interval will last until the heart rate drops to the pre-determined threshold (percent of max HR). This is a much more efficient mode of training. It accounts for individuals' varying fitness levels, as well as providing a concrete, measurable method of interval training that can be strategically adjusted depending on the workout performance. In other words, you will now have a solid basis for where and how to draw the line. Measure how long it takes for the HR to drop to the desired recovery rate and you will see drastic results.

If you are a beginner, or you find the Karvonen formula too complicated, the next best thing would be to adjust your interval times based on fitness level. Remember, the idea is that you work to an elevated heart rate and rest until you reach a pre-determined recovery HR. You can use timed intervals with rest to work ratios of 3:1 for beginners (45s rest: 15s work), 2:1 for average fitness levels (30s rest: 60s work) and 1:1 advanced (60s rest: 60s work). These of course, are not the only intervals sets that make sense; however, they also consider “the who" and attempt to create a work to rest (interval) workout that intends to push people to their limit without overexerting themselves, as well as gauging how well they are recovering. Remember, the longer the intervals, the less time a person may need to recover (due to the obvious lack of exercise intensity), whereas shorter more intense interval sets may require much longer to recover to do the increased energy output.

The fast food method is unfortunately very common in today's culture, where we constantly sacrifice our ultimate goal (health and physical/mental fitness and progression in this case), for immediate yet temporary results. Fitness and health are ever changing fields. Stay informed and your performance, appearance and health will be better off. Work hard…but train smart! Remember, if you're not measuring, you're just guessing…


Robert A. Robergs, Roberto Landwehr. The surprising history of the “HRmax=220-age" equation. JEPonline. 2002;5(2):1-10

William D. McArdle, Frank I. Katch, Victor L. Katch (2009). Exercise Physiology: Nutrition, Energy, and Human Performance