Many studies of a high quality, high protein beverage during and after exercise, with dairy-based drinks enriched with whey proteins often taking front stage, have shown a beneficial effect of their consumption. One particular interest for researchers is the essential amino acid Leucine contained in those products.

Leucine is an essential amino acid that stimulates skeletal muscle protein synthesis or decrease muscle protein breakdown.

Physical exercise causes muscle breakdown especially in resistance exercises. Many athletes have long experimented with methods to decrease the physiologic effects.

Two papers published in the American journal of Clinical Nutrition, report such results of two independent studies conducted to understand better how amino acids influence protein synthesis in recreational athletes.

In the first study, researchers led by Stuart Phillips (McMaster University) investigated whether post exercise muscle protein synthesis is different when a large, single dose of whey protein (25 g) is consumed immediately after activity compared with when smaller doses (2.5 g) are consumed 10 times over an extended period. The idea with the small "protein shots" was to mimic how another milk protein, casein, is digested. Participants (8 men; mean age: 22 y) performed 8 sets of 8 repetitions on a leg-extension machine; each subject participated in both dietary treatment regimens.

In the second study led by Stefan Pasiakos from the US Army Research Institute of Environmental Medicine, active-duty military personnel (7 men and 1 woman; mean age: 24 y) consumed a high-protein beverage (10 g protein as essential amino acids) containing 1.87 or 3.5 g Leucine while exercising on a stationary bicycle. In both studies, post exercise muscle protein synthesis was evaluated.

The first study found consumption of large doses of the whey protein immediately increased muscle protein synthesis after exercise more than when periodic smaller doses of protein were consumed. In the second study, muscle protein synthesis was 33 percent greater after consumption of the Leucine-enriched protein beverages that after the lower Leucine drink.

The researchers concluded that muscle metabolism after exercise can be manipulated via dietary means. Immediate post exercise consumption appears to be the best for most optimal protein synthesis.

Leucine may play an especially important role in stimulating muscle growth in the post activity recovery period.