Too Much Of A Good Thing

It’s a common cardio blunder: performing frequent, drawn-out sessions in the attempt to burn more body fat, faster. Though your sweat-soaked lululemons seem like a surefire sign that you’re stripping off unwanted fat, don’t expect that to trickle down to a leaner physique over the long haul. Your endless treks on the treadmill could actually be undermining your fat-loss efforts.

Get Up to Speed

While the slow-and-steady approach will have you burning through calories, it will also cost you valuable muscle. Long bouts on the treadmill cause oxidative stress and spur the release of free radicals, which play a role in tired, sore muscles during and after cardio sessions. That’s because the body ramps up the release of these free radicals at a rate that exceeds its ability to maximize its own defense. So even though you’re blazing calories, the resulting muscle damage, fatigue and compromised immune function far outweigh the benefit.

Too much cardio also causes your body to churn out cortisol in excess, leaving muscles drenched in the muscle-wasting hormone. This could send you spiraling into a state in which lean muscle is broken down, you gain fat, compromise your immune system and reduce your ability to repair tissue damage following a workout. Plus, chronic cortisol exposure often leads to increased appetite and cravings for certain foods — especially sweets — so you’ll constantly feel hungry.

The result: You’ll set off physiological alarms that cause your metabolism to slow, so you’ll end up burning less body fat. And while many experts argue that you incinerate more pounds using this method, scientific evidence confirms you’ll burn significantly more body fat by curbing duration and bumping up intensity.

A study from the University of New South Wales in Australia tracked the effects of high-intensity cardio in 45 women over a 15-week period. The women were divided into two groups: One group did 20 minutes of eight-second sprints followed by 12 seconds of rest, while the other did 40 minutes at a steady rate. At the end of the study, researchers found that the women who did the high-intensity-interval-training protocol lost significantly more body fat than their lower-intensity counterparts. More interestingly, researchers noted that the women who performed HIIT burned more abdominal and lower-body fat (in the trunk and legs) while gaining more lower-body muscle. The women who performed steady-state cardio actually gained more lower-body fat.

Unlike the slow-and-steady approach, cardio at a faster, harder pace also can boost metabolism even after you jump off the treadmill, ensuring you’re continuing to burn fat long after the workout is over. If you’re looking to get lean fast without burning through or compromising muscle function, it’s an easy choice. Go hard, not long.

Ditch This:

Walking on the treadmill at a slow to moderate speed for 45 to 60 minutes daily.

HIIT This:

Up to 20 minutes of high-intensity interval training using a 2:1 ratio of work to active rest, every two to three days. (For example, if you do a 20-second interval, do 10 seconds of active rest.)