• disuse atrophy;
  • immobilization;
  • myostatin;
  • skeletal muscle



The impact of disuse on the loss of skeletal muscle mass and strength has been well documented. Given that most studies have investigated muscle atrophy after more than 2 weeks of disuse, few data are available on the impact of shorter periods of disuse. We assessed the impact of 5 and 14 days of disuse on skeletal muscle mass, strength and associated intramuscular molecular signalling responses.


Twenty-four healthy, young (23 ± 1 year) males were subjected to either 5 (= 12) or 14 (= 12) days of one-legged knee immobilization using a full leg cast. Before and immediately after the immobilization period, quadriceps muscle cross-sectional area (CSA), leg lean mass and muscle strength were assessed, and biopsies were collected from the vastus lateralis.


Quadriceps muscle CSA declined from baseline by 3.5 ± 0.5 (< 0.0001) and 8.4 ± 2.8% (< 0.001), leg lean mass was reduced by 1.4 ± 0.7 (= 0.07) and 3.1 ± 0.7% (< 0.01) and strength was decreased by 9.0 ± 2.3 (< 0.0001) and 22.9 ± 2.6% (< 0.001) following 5 and 14 days of immobilization respectively. Muscle myostatin mRNA expression doubled following immobilization (< 0.05) in both groups, while the myostatin precursor isoform protein content decreased after 14 days only (< 0.05). Muscle MAFBx mRNA expression increased from baseline by a similar magnitude following either 5 or 14 days of disuse, whereas MuRF1 mRNA expression had increased significantly only after 5 days.


We conclude that even short periods of muscle disuse can cause substantial loss of skeletal muscle mass and strength and are accompanied by an early catabolic molecular signalling response.