Several studies published in recent years show that combining aerobic and anaerobic exercise'such as weight training'limits gains in muscular size and strength. The usual explanation is that combined exercise favors metabolic pathways that interfere with the increased muscle protein synthesis required for building muscle and strength. Another possible explanation is simply overtraining, leading to an increased release of the adrenal hormone cortisol, which promotes muscle catabolism, or breakdown.
Some scientists suspect that the problem involves a depletion of the energy stores needed to power various recovery mechanisms and fuel anaerobic workouts. The popular supplement creatine is thought to work by increasing muscle energy reactions. So the question is whether using a creatine supplement would help blunt the negative effects of aerobics on anaerobic exercise. That was the focus of a study presented by Brazilian sports science researchers at the 2004 meeting of the American College of Sports Medicine.1
Fourteen young women, average age 20, were divided into placebo or creatine groups. Those in the creatine group received 20 grams of creatine daily for five days, followed by three grams of creatine daily for another seven days. The subjects were tested for strength and endurance before they got the creatine.
After 12 days the subjects participated in an aerobic testing procedure, in which they were told to run as far as they could in 20 minutes. Shortly after that run they were tested for one-rep-maximum strength on the leg press.
Those in the placebo group showed declines in strength after the run, while those in the creatine group showed no strength loss. The authors attributed that effect to a maintenance of muscle energy stores that would otherwise have been depleted by the aerobic exercise. This upgraded muscle energy allowed those in the creatine group to maintain their strength even after engaging in maximal aerobics. IM
1 Aoki, M., et al. (2004). Creatine supplementation attenuates the adverse effect of endurance exercise on subsequent resistance exercise performance. Med Sci Sports Exer. 36:(Supp)S334-S335.