Some trainers warn against lifting weights and going for a run on the same day. Mixing them, they say, will either limit the growth of the muscles, or reduce the endurance benefits of the run—what’s known as “muscle interference” or “exercise antagonism.”
A Swedish study, published in Medicine and Science in Sports and Exercise, investigated this effect in young, healthy men. Researchers asked the men to pedal a stationary bike for 45 minutes with one leg, followed six hours later by leg extensions with both legs. In this way, one leg received a combined aerobic and resistance workout, while the other had only strength training.
Muscle biopsies showed that the combined group and the strength-only group showed similar molecular and biomechanical responses in the cells. The scientists concluded that “aerobic exercise can precede resistance exercise on the same day without compromising” muscle building.
In a separate Canadian study, published in the Journal of Applied Physiology, sedentary middle-aged men completed one of three trials—40 minutes of stationary biking; strenuous leg extensions; or leg extensions followed immediately by biking. In the combined group, the men worked at only 50 percent of the effort of the individual sessions.
The researchers found no “muscle interference” when aerobic and strength were combined. Signals of energy production and muscle building in the cell were the same with the combined group as with the individual sessions. This occurred even though the men were working at only half the effort.
Both studies indicate that, at a cellular level at least, mixing aerobic and strength training will not negatively impact your muscles. This finding should make it easier to squeeze your workouts into your schedule without worrying about which should come first, aerobic or strength.