Temporal Muscle-Specific Disuse Atrophy during One Week of Leg Immobilization

Abstract

Purpose Musculoskeletal injuries necessitate periods of disuse (i.e. limb immobilization) during which rapid skeletal muscle atrophy occurs. The relative susceptibility of different muscles of the thigh to disuse atrophy remains uninvestigated. We assessed muscle disuse atrophy of individual thigh muscles throughout one week of unilateral knee immobilization.

Methods Thirteen healthy, young (20.2±0.6 y) men underwent 7 days of unilateral leg immobilization via knee bracing. MRI scans were performed bilaterally prior to, and following 2 and 7 days of immobilization to determine the volume and anatomical cross-sectional area (aCSA) of the individual muscle groups of the upper legs.

Results In contrast to the control leg, total thigh muscle volume had decreased by 1.7±0.3 (P<0.01) and 5.5±0.6% (P<0.001) in the immobilized leg after 2 and 7 days of disuse, respectively. Muscle loss was significantly greater in the M. quadriceps (day 2; 1.7±0.3 (P<0.05) and day 7; 6.7±0.6%) when compared with the M. hamstrings (day 2; 1.4±0.2% (P<0.01) and day 7; 3.5±0.3%) following 7 days of disuse (P<0.001). Individual muscles of the thigh exhibited different atrophy rates with the M. vastus lateralis aCSA showing the greater (2.6±0.4 and 7.2±0.8%), and the M. gracilis the lesser (1.1±0.7 and 2.3±1.0%) decline following 2 and 7 days of immobilization, respectively (P<0.01).

Conclusion Thigh muscle disuse atrophy occurs rapidly and is already evident within 2 days of leg immobilization and progresses at a similar rate over the next 5 days (~0.8% muscle loss per day). M. quadriceps muscle shows more atrophy when compared with the M. hamstrings.