Leucine Supplementation Does Not Attenuate Metabolic Or Functional Declines Following 7-days Of Unilateral Lower-limb Immobilisation.

Abstract

Unavoidable periods of physical inactivity (i.e. illness/injury) lead to muscle atrophy and functional declines, which likely stem from alterations in both anabolic signaling processes and oxidative metabolism. Preventing such declines is important to reduce the risk of re-injury and preserve musculoskeletal health across the lifespan. PURPOSE: To determine the effectiveness of high-dose leucine supplementation to preserve muscle mass, strength, and morphology following 7-days of unilateral knee immobilisation. METHODS: Sixteen healthy, recreationally active males (23±1yrs) underwent 7-days of unilateral knee immobilisation, with (LEU; n=8) or without (PLA; n=8) thrice daily leucine supplementation (15g/d). Strength and compartmental tissue composition were assessed prior to and following immobilisation. Muscle biopsy samples obtained immediately following immobilisation were used to determine muscle fibre morphology as well as key indicators of mitochondrial function between the control (CTL) and immobilised (IMB) limbs. RESULTS: Leg fat-free mass was reduced in the IMB leg following immobilisation (-3.6±0.5%; P<0.05) in both the LEU and PLA conditions (P>0.05), with no such alterations noted in the CTL leg (-0.6±0.5%; P>0.05). Isometric knee extensor strength declined following immobilisation (P<0.01), with a greater (P<0.05) and equivocal decline in the IMB (-27.9±4.4%) vs. CTL (-14.3±4.4%) leg in both the LEU and PLA group (P>0.05). Following immobilisation, type II fibre cross sectional area was significantly lower in the IMB vs. CTL limb (5561.49±465.97 vs. 6319.9±412.9μm2; P<0.05) but not in type I fibre cross sectional area (4805.5±324.3 vs. 5424.95±323.63μm2; P>0.05), with no differences between treatment groups (P>0.05). A significant Group*Leg interaction was identified for mitochondrial complex I phosphorylating respiration (Pi; P<0.05). However, post-hoc analysis revealed no differences in Pi in the IMB vs. CTL limb in either the PLA (FC=1.20±0.19, P=0.06) or LEU (FC=0.87±0.27, P=0.87) group. CONCLUSION: Leucine supplementation, even at a high-dose (15g/d), does not appear to attenuate declines in leg fat-free mass, strength, muscle morphology or mitochondrial respiration following 7-days of unilateral knee immobilisation.