"The study does not mean exercise is bad for you," Columbia University's Andrew Marks, MD, says in a news release.
The findings might do more than explain why muscles need rest after intense training. The research could also lead to a new drug for heart failure.
Marks' team put mice on an intense training regimen that included swimming in a pool and scampering along a treadmill.
During high-intensity exercise, the mice's muscles leaked calcium, and when that happened, the mice's muscle endurance nose-dived. Their muscle strength recovered with three days of rest.
Exercise has "numerous positive benefits," Marks and colleagues write. "On the other hand, exhausting exercise, such as that performed by a marathon runner or a long-distance cyclist, results in significant muscle damage and can impair task performance for days or weeks."
New Heart Failure Drug?
Athletes can rest to let their muscles regain their strength. But people with heart failure may experience the same calcium leakage and weakness while idle.
"People with chronic heart failure are subject to this same kind of muscle leak and damage constantly, even without doing any exercise," Marks says in a news release.
Marks and colleagues have already tested the experimental drug in rodents that developed heart failure because of a heart attack. The researchers plan to test theÂ experimental drug in people with heart failure, according to the news release.