Leucine Supplementation Does Not Attenuate Skeletal Muscle Loss during Leg Immobilization in Healthy, Young Men.

BACKGROUND: Short successive periods of physical inactivity occur throughout life and contribute considerably to the age-related loss of skeletal muscle mass. The maintenance of muscle mass during brief periods of disuse is required to prevent functional decline and maintain metabolic health.

OBJECTIVE: To assess whether daily leucine supplementation during a short period of disuse can attenuate subsequent muscle loss in vivo in humans.

METHODS: Thirty healthy (22 ± 1 y) young males were exposed to a 7-day unilateral knee immobilization intervention by means of a full leg cast with (LEU, n = 15) or without (CON, n = 15) daily leucine supplementation (2.5 g leucine, three times daily). Prior to and directly after immobilization, quadriceps muscle cross-sectional area (computed tomography (CT) scan) and leg strength (one-repetition maximum (1-RM)) were assessed. Furthermore, muscle biopsies were taken in both groups before and after immobilization to assess changes in type I and type II muscle fiber CSA.

RESULTS: Quadriceps muscle cross-sectional area (CSA) declined in the CON and LEU groups ( p < 0.01), with no differences between the two groups (from 7712 ± 324 to 7287 ± 305 mm² and from 7643 ± 317 to 7164 ± 328 mm²; p = 0.61, respectively). Leg muscle strength decreased from 56 ± 4 to 53 ± 4 kg in the CON group and from 63 ± 3 to 55 ± 2 kg in the LEU group (main effect of time p < 0.01), with no differences between the groups ( p = 0.052). Type I and II muscle fiber size did not change significantly over time, in both groups ( p > 0.05).

CONCLUSIONS: Free leucine supplementation with each of the three main meals (7.5 g/d) does not attenuate the decline of muscle mass and strength during a 7-day limb immobilization intervention.