Increasing or maintaining muscle mass is of great importance for populations ranging from athletes to patients and elderly. Resistance exercise and protein ingestion are two of the most potent stimulators of muscle protein synthesis. Both the physical characteristic of proteins (e.g. different digestion rates of whey and casein) and the amino acid composition, affects the potential of a certain protein to stimulate muscle protein synthesis. Given its superior ability to rapidly increase blood leucine concentrations to high levels, whey is often considered the most potent protein source to stimulate muscle protein synthesis. Native whey protein is produced by filtration of unprocessed milk. Consequently, native whey has different characteristics than WPC-80, which is exposed to heating and acidification. Because of the direct filtration of unprocessed milk, native whey is a more intact protein compared with WPC-80. Of special interest is the higher amounts of the highly anabolic amino acid leucine in native whey.~The higher levels of leucine can be of great interest for elderly individuals as some studies in elderly has shown an anabolic resistance to the effects of protein feeding and strength training. By increasing levels of leucine one might overcome this anabolic resistance in the elderly.~The aim of this double-blinded, randomized, partial cross-over study is to compare the acute fractional protein synthesis and intracellular signaling response to a bout of strength training and intake of 20 grams of protein from either native whey, whey protein concentrate 80 or milk, in young and old individuals. Furthermore, the investigators wil investigate fractional protein breakdown, markers of protein breakdown, amino acid concentrations in blood.~The investigators hypothesize that native whey will induce a greater anabolic response than whey protein concentrate 80, and that whey protein concentrate 80 will give a stronger anabolic response than milk.
The aim of this study is to investigate the acute anabolic effects of native whey, whey protein concentrate 80 (WPC-80) and milk after a bout of strength training in young and elderly. The investigators hypothesize that native whey will give a greater stimulation of muscle protein synthesis and intracellular anabolic signaling than WPC-80, and that WPC-80 will give a stronger stimulus than milk.