People want dramatic workout results as quickly as possible. That's why High-Intensity Interval Training (HIIT) has worked its way into the mainstream and was named the top fitness trend in 2014 by the American College of Sports Medicine.
But like other forms of exercise, you can do too much of a good thing. "Most of the time when we look at trends, we think they're based on marketing," says Nick Tumminello, owner of Performance University. "HIIT is supported by scientific evidence. But when things become a trend, they get taken too far."
What Is HIIT?
HIIT workouts involve short bursts of intense exercise followed by periods of rest or active recovery. You work at or above your VO2 max—or even harder during a similar style of training called SMIT—to promote rapid improvements in conditioning. The high-intensity activity burns more calories faster than cardio workouts like jogging, causing your body to continue burning calories even after you finish your session.
One of the most popular forms of HIIT is the Tabata workout, which involves eight 20-second sets of intense activity interspersed with 10-second rest periods. As with other types of HIIT, the exercise you perform can vary. Traditionally, this style of training calls for an endurance exercise, like Sprinting or Biking. However, the concept has been applied to strength exercises such as Squats, Push-Ups or Burpees, to simultaneously improve strength, endurance and overall fitness.
Can You Do Too Much HIIT?
HIIT workouts are intense—after all, "high-intensity" is part of the name. But according to Tumminello, if you push your body at this level too frequently, it may break down. Like any other exercise or method of training, there will be consequences if you do too much.
HIIT workouts are designed to stress your body, causing your muscles to adapt to the challenge and get bigger or stronger, or your cardiovascular system's efficiency to improve. However, Tumminello says there's a point where stress becomes distress.
"The more work you do at a higher intensity, the more recovery you need," he explains. "We want to create enough stress to stimulate improvement, but if we create distress, then the body is no longer able to adapt, and it becomes overtrained."
This leads to a cascade of problems—muscle breakdown, grogginess, fatigue and increased risk for injury—not anything you want if you're an athlete or if you're committed to a workout program.
Also, most HIIT workouts are performed with body weight or light weights. If your primary goal is to get bigger and stronger, HIIT is not a substitute for heavy strength-training workouts.
How Much HIIT is OK?
It all comes down to your individual needs. If you want to lose weight or improve your general fitness, Tumminello recommends no more than three HIIT workouts per week. If you're also strength training, do no more than two HIIT workouts to account for the demands of your other training sessions.
If you're an athlete, consider that HIIT workouts typically involve mostly lower-body exercises. So schedule HIIT as far away from practices as you can. During your season, avoid HIIT workouts altogether.
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