The time course of disuse muscle atrophy of the lower limb in health and disease

Short, intermittent episodes of disuse muscle atrophy (DMA) may have negative impact on age related muscle loss. There is evidence of variability in rate of DMA between muscles and over the duration of immobilization. As yet, this is poorly characterized. This review aims to establish and compare the time-course of DMA in immobilized human lower limb muscles in both healthy and critically ill individuals, exploring evidence for an acute phase of DMA and differential rates of atrophy between and muscle groups. MEDLINE, Embase, CINHAL and CENTRAL databases were searched from inception to April 2021 for any study of human lower limb immobilization reporting muscle volume, cross-sectional area (CSA), architecture or lean leg mass over multiple post-immobilization timepoints. Risk of bias was assessed using ROBINS-I. Where possible meta-analysis was performed using a DerSimonian and Laird random effects model with effect sizes reported as mean differences (MD) with 95% confidence intervals (95% CI) at various time-points and a narrative review when meta-analysis was not possible. Twenty-nine studies were included, 12 in healthy volunteers (total n = 140), 18 in patients on an Intensive Therapy Unit (ITU) (total n = 516) and 3 in patients with ankle fracture (total n = 39). The majority of included studies are at moderate risk of bias. Rate of quadriceps atrophy over the first 14 days was significantly greater in the ITU patients (MD similar to 1.01 95% CI similar to 1.32, similar to 0.69), than healthy cohorts (MD similar to 0.12 95% CI similar to 0.49, 0.24) (P < 0.001). Rates of atrophy appeared to vary between muscle groups (greatest in triceps surae (similar to 11.2% day 28), followed by quadriceps (similar to 9.2% day 28), then hamstrings (similar to 6.5% day 28), then foot dorsiflexors (similar to 3.2% day 28)). Rates of atrophy appear to decrease over time in healthy quadriceps (similar to 6.5% day 14 vs. similar to 9.1% day 28) and triceps surae (similar to 7.8% day 14 vs. similar to 11.2% day 28), and ITU quadriceps (similar to 13.2% day 7 vs. similar to 28.2% day 14). There appears to be variability in the rate of DMA between muscle groups, and more rapid atrophy during the earliest period of immobilization, indicating different mechanisms being dominant at different timepoints. Rates of atrophy are greater amongst critically unwell patients. Overall evidence is limited, and existing data has wide variability in the measures reported. Further work is required to fully characterize the time course of DMA in both health and disease.

Automated summary

Short, intermittent episodes of disuse muscle atrophy (DMA) may have negative impact on age-related muscle loss, with evidence of variability in the rate of DMA between muscles and over the duration of immobilization. Studies found that the rate of quadriceps atrophy was significantly greater in critically ill patients compared to healthy individuals, with the greatest atrophy observed in the triceps surae muscle group over 28 days. Further research is needed to fully characterize the time course of DMA in both health and disease.