by Jeff S. Volek, Ph.D., R.D.
Only one study has determined the dose response effect of protein provided after resistance exercise. Using egg protein, the study showed that muscle protein synthesis reached a plateau when 20 grams of protein was ingested. When 40 grams was ingested, there was no further increase in muscle protein synthesis.
A similar study was recently conducted with whey protein isolate. Subjects consumed whey after a bout of single leg knee extensions, using the non-exercised leg as a control. The subjects were older, with 
an average age of 70 years.
After exercising one leg, they consumed a drink containing 0, 10, 20 or 40 grams of whey protein isolate. Measures of muscle protein synthesis were determined for 4 hours after exercise in the control (non-exercised) leg (to assess the effects of simply ingesting whey without exercise), and in the exercised leg (to assess the effects of whey plus resistance exercise). Rates of muscle protein synthesis were higher in the exercised leg compared to the control leg at all doses of whey, consistent with the synergistic effect of whey and exercise.
In the control (non-exercised) leg, there was a significant increase in muscle protein synthesis with the 20 gram dose, but no further increase with 40 grams. In the exercised leg, there was a significant increase in muscle protein synthesis with 20 grams of whey, and a further 32% increase with the 40 gram dose. This indicates that 20 grams of whey was necessary to significantly increase muscle protein synthesis at rest in elderly subjects, but after resistance exercise, a higher dose may be needed to achieve a maximal increase in muscle protein synthesis.
