Whole body and plasma protein synthesis in exercise and recovery in human subjects.

The effect of 4 h of exercise at 40% of maximal oxygen consumption (VO2 max) on protein metabolism was assessed in normal volunteers maintained on a diet containing 42 kcal.kg-1.day-1 and either 0.9 or 2.5 g protein.kg-1.day-1. Primed constant infusions of [1,2-13C]-leucine and [15N]glycine enabled the quantitation of whole body protein turnover and also the fractional synthetic rates (FSR) of albumin, fibrinogen, and fibronectin. In subjects who did not exercise, the fractional synthetic rates (%/day) on normal and high-protein intakes, respectively, were as follows: albumin, 10 +/- 1 and 9 +/- 1; fibrinogen, 21 +/- 3 and 18 +/- 1; and fibronectin, 31 +/- 3 and 34 +/- 3. Neither exercise nor recovery had an effect of whole body protein turnover or on albumin FSR, but the FSR of fibronectin was significantly elevated at the end of exercise, and fibrinogen was significantly elevated in recovery. Dietary protein intake had no major effect on the response to exercise. Thus, in response to exercise, there is a stimulation of the synthesis of some acute phase proteins, which may be a mechanism whereby nitrogen resulting from muscle protein breakdown is spared.