Friday, April 20, 2012

Lose Muscle With Aerobics? by Jerry Brainum

In bodybuilding, it’s axiomatic that doing aerobics promotes loss of muscle. The theory is that aerobic exercise depresses muscle protein synthesis—or maybe it lowers anabolic hormones, such as testosterone. Like a lot of bodybuilding axioms, however, it ain’t necessarily so.

In fact, one study found that subjects who did strenuous aerobics for an hour over the course of three days had levels of muscle protein synthesis similar to those that occur after weight training. Based on that unexpected finding, a new study was designed to measure skeletal muscle breakdown in the thighs after an hour of strenuous one-legged aerobic exercise.

The study, which featured five healthy young men, was reported at the 2006 ACSM meeting. The muscle protein breakdown was measured at rest, and at six, 24, 48 and 72 hours after the exercise. Muscle protein breakdown was determined by the excretion of 3-methylhistidine, a substance produced only in contractile muscle proteins.

      The results revealed no difference in muscle protein breakdown at any point after the exercise. On the other hand, as in past studies, muscle protein synthesis increased, just as it does after weight training. The authors think that happened to offset the breakdown that would normally occur after strenuous exercise.
    A practical application of those findings is that doing higher intensity aerobics, such as interval training, characterized by alternating periods of high and low intensity, may not only produce greater cardiovascular benefits than the usual steady-state aerobics but also blunt muscle protein loss.

1 Haus, J.M., et al. (2006). The effect of strenuous aerobic exercise on skeletal muscle myofibrillar proteolysis in humans. Med Sci Sports Exerc. 38:S549

©,2012, Jerry Brainum.Any reprinting in any type of media, including electronic and foreign is expressly prohibited.