High Intensity Exercise: Too Much of a Good Thing?

When it comes to personal fitness, the duration of quarantine had varying effects - while some people worked out regularly, researchers have found that overall, physical activity levels dropped worldwide.

Of course, the endorphins from a workout are something everyone can use these days, but recent studies show frequent high intensity interval training (also known as HIIT) can sometimes provide too much of a good thing. According to a research article published on March 18, “excessive exercise training induces substantial mitochondrial respiratory impairment… (which) is associated with impaired glucose tolerance.” Mitochondria function as energy wheels inside of cells and damage to it can cause blood sugar dysfunction.

Therapy Supervisor Rick Fame, MS, PT who focuses on sports and orthopaedic injuries at Rochester Regional Health’s Physical Therapy & Rehabilitation Center at the Midtown Athletic Club, says the risk all depends on the type of workout.

Moderate exercise and HIIT

“Moderate exercise, four to five times a week, is actually proven to be very effective for weight loss and overall health benefits,” he says. “Whereas many intense workouts within a shorter time span can lead to injury or ineffectiveness if done daily.”

Another study published in December 2020 supports this theory, pointing to moderate exercise as more beneficial for the metabolism, resulting in more weight loss overall.

So, what’s the difference between moderate exercise and high intensity interval training? Let’s break down the terms.

A High Intensity Interval Training (HIIT) is categorized as the most effective workout in the shortest amount of time. It usually involves a warmup, followed by several-minute bursts of high intensity workouts - jogging, brisk walking, swimming, cardio, spinning - where your heart rate extends beyond 80% of its capacity. These bursts are interspersed with cool downs, and repeated for a total of 30-40 minutes total. Crossfit is a good example of HIIT.

Moderate Exercise, which is still considered the most healthy option, is sustained activity at a comfortable pace for 30-40 minutes three to four days per week - walking, jogging, cycling, swimming, etc.

The December research study found that a group who participated in moderate exercise for roughly 2.5 hours per week lost more body fat, had lower blood pressure, and a greater metabolic reaction than those who participated in HIIT for less than an hour per week.

So is all HIIT bad?

“Not at all,” says Fame. “When done correctly and a few times per week, HIIT exercise is extremely good for heart health. The key is not to overdo it.”