Abstract:
Background: Muscle mass maintenance is regulated by an intricate balance between protein synthesis (MPS) and breakdown (MPB). Muscle disuse results in the loss of muscular strength and size, due to an imbalance between MPS and MPB. Protein ingestion stimulates MPS, although it is not established if protein is able to attenuate muscle loss with immobilisation (IM) or influence the recovery consisting of ambulatory movement followed by resistance training (RT). Methods: Thirty healthy middle-aged men (49.9 ± 0.6 yrs) were subjected to 14 days of unilateral leg IM, 14 days of ambulatory recovery (AR), and subsequent six RT sessions over 14 days. During the intervention subjects were randomised to consume an additional 20 g of dairy protein or placebo with a meal. Results: Isometric knee extension declined from baseline from 212 ± 19 and 231 ± 14 Nm in the protein and placebo groups, respectively to 154.5 ± 14 and 167.6 ± 10 Nm in the protein and placebo groups, respectively (P<0.001), partially recovered with AR 194.2 ± 15.2 and 202.5 ± 8.8 Nm in the protein and placebo groups, respectively (P<0.001), with no effect of the supplementation. Thigh muscle cross-sectional area decreased from baseline following IM from 16272 ± 863.2 mm2 in the protein and 16673 ± 667.80 mm2 in the placebo group to 15625 ± 815.54 and 15954.62 ± 611.75 mm2 in the protein and placebo groups, respectively; partially recovered above post immobilisation values with AR, 15923.94 ± 818.06 mm2 and 16283.81 ± 598.16 mm2 in the protein and placebo groups, respectively and increased above baseline with RT, 16684.90± 825.02 and 16881.32 ± 633.28 mm2 in the protein and placebo groups, respectively, with no treatment effect. Conclusion: Protein supplementation did not attenuate muscle strength and muscle mass loss during muscle disuse or potentiate recovery, but rehabilitation of muscle function and size was fully accomplished with additional 2 weeks of RT.