Light‐load resistance exercise increases and prolongs the elevation in myofibrillar protein synthesis rate in human skeletal muscle induced by continuous protein feeding

Abstract

We determined the effect of light‐load resistance exercise (LL‐RE) on the prolonged stimulatory effect of orally ingested protein on myofibrillar protein fractional synthesis rate (myoFSR). Ten healthy, young males were given a primed‐continuous infusion of 13C‐leucine in the overnight fasted state. The subjects performed 10 sets of 36 unilateral knee extensions at 16% of one‐repetition maximum while the contralateral leg remained rested. Hereafter, 11 hourly repeated boluses of 10% 13C‐leucine labelled milk protein was ingested each containing 0.1 g protein·kg−1 lean body mass. Frequent blood samples and five biopsies from each vastus lateralis muscle were obtained at 30, 180, 330, 480 and 630 min post exercise. Leucine tracer enrichments in myofibrillar protein as well as in muscle free amino acid were measured as well as plasma amino acid concentrations. The repeated protein ingestion increased plasma leucine and essential amino acids as a mean across the 10‐hr period by 39±9 and 32±5%, respectively compared to fasting, basal state (p<0.05). LL‐RE improved myoFSR compared to rest in the protein‐fed state (p<0.05) and an exercise‐time interaction tended to appear (p=0.08), demonstrating that the myoFSR dropped after 480 min in the resting muscle only. In conclusion, brief contractions prolong and further improve the amino acid stimulated elevation of myofibrillar protein synthesis rate.Research funding: Danish Medical Research Council.