Science Says Your HIIT Habit Might Be Getting Out of Hand

Woman working out at the gym

For those of us with a busy schedule, high-intensity interval training, or HIIT for short, is a godsend. It’s quick, requires little to no equipment, and it can be done just about anywhere. Lots of gyms are offering HIIT classes in increasing numbers, and the fat-burning, lung-expanding benefits of interval training are numerous. Of course, as with many a good thing, there is such a thing as going a little overboard with your HIIT workout. Specifically, going hard at the gym but then neglecting to make time for recovery here and there could have some pretty adverse effects on both your health and your progress.

A recent study conducted by Les Mills, the creator of research-based group fitness classes, and Jinger Gottschall, Ph.D., an associate professor of kinesiology at Penn State University, found that all you have to do is go over 40 minutes of HIIT training per week for you to be at greater risk of injury and overtraining. Overtraining generally occurs when you eschew a rest and recovery day to keep working out, and can have symptoms like stress, missed menstrual periods, and sleep loss. All of this, of course, is in addition to a greater risk of injury.

Another way to tell if your high-intensity workout is becoming a little too intense is if you begin to notice that your progress has stopped or even started to reverse. Maybe your usual weights feel heavier than normal, your run feels twice as long, or you might be feeling nauseous after just the warmup. While your first instinct might be to try and power through when you’re not feeling totally up to your workout, the reality is that any of these scenarios could be a sign that your body just needs a day to recover – which, aside from helping you bounce back after some hard work, gives your body a chance to build some muscle, too.

Still, limiting yourself to a mere 30 or 35 minutes of high-intensity training per week sounds pretty scarce, to say the least.  So what should you do to achieve the right amount of HIIT without overtraining? First, it is important to note that even one session per week is enough to see incredible results, when done in conjunction with other workout routines throughout the week. This is because the muscle-building and fat-burning powers of HIIT work long after your workout is finished, while longer, more aerobic workouts don’t necessarily boast the same kind of long-term benefits that a good HIIT session would.

Plus, to be clear, 30 minutes of high-intensity training per week doesn’t necessarily need to translate into just a single session of HIIT training. Most HIIT routines only spend about 10-15 minutes in the max heart rate capacity zone, which is where your heart is working at 85-100% of its potential capacity. This means that two HIIT classes per week is probably ideal. As for the parts of your week that aren’t spent tackling box jumps and sprints? They’re probably best spent with some strength training or yoga.