Attenuation Of Muscle Impairments Relates To Functional Improvements During Rehabilitation Following Immobilization.

Abstract

PURPOSE: The purpose of this study was to 1) quantify the effects of immobilization and subsequent rehabilitation training on muscle size and strength about the ankle and 2) determine the extent to which improvements in physical function relate to gains in strength in ankle plantar- and dorsi-flexor muscles. We hypothesized that greater relative changes in both muscle strength and size would be seen in the plantar- versus the dorsi-flexor muscle group, reflective of the anti-gravity responsibilities of the plantar flexor muscles. METHODS: Following immobilization, fourteen subjects enrolled in a standardized rehabilitation program involving progressive resistance exercises and treadmill walking. Plantar- and dorsi-flexor strength were determined via dynamometry and functional ability was assessed during stair climbing and over ground walking immediately prior to, during and following rehabilitation. In addition, maximum cross-sectional area (CSA) of the muscles that elicit ankle plantar- and dorsi flexion were determined via magnetic resonance imaging (MRI). RESULTS: A greater degree of atrophy was noted in the plantar- compared to the dorsi-flexors following immobilization (25.5 ± 6.4% versus 20.5 ± 3.8%, respectively). Similarly, plantar flexor strength was reduced 73.3 ± 12.4% relative to the contralateral limb, while dorsi-flexor strength was reduced 52.1 ± 9.9%. Following rehabilitation, increases in both plantar (55.1 ± 14.9%) and dorsi-flexor (29.9 ± 8.5%) strength were noted. Increased functional ability was also realized, with improvements in both stair climbing and over ground walking velocity following rehabilitation. Of note, recovery of function significantly correlated to the recovery of dorsi flexor (R2 = 0.79 and 0.85) and plantar flexor (R2 = 0.86 and 0.88) strength, respectively. CONCLUSIONS: A discrepancy in the hierarchy of response was found between changes in muscle size and strength in the ankle plantar- versus dorsi-flexor muscles following immobilization. Rehabilitation induced improvements in muscle strength were realized in both the plantar and dorsi-flexion, with improvements significantly related to improved functional performance.