Single-Leg Disuse Decreases Adult Skeletal Muscle Strength and Size: A Systematic Review and Meta-Analysis

Abstract

Background: Single-leg disuse results in a decrease in skeletal muscle strength and size increasing the risk for disease and disability. In order to better understand the mechanisms driving skeletal muscle loss with single-leg disuse, researchers employ a variety of single-leg disuse models and apply them to healthy adults. However, there is a significant range in the decline in skeletal muscle strength and size both within and between single-leg disuse models in such studies. This variability renders it difficult to estimate accurate effect sizes that could be used to generate power calculations for future work. Purpose: To conduct a systematic review and meta-analyses to quantify changes in skeletal muscle strength and size in response to single-leg disuse. Another purpose of the present thesis was to explore the potentially modulating effects of duration, experimental model, age of participants, and biological sex of participants on changes in skeletal muscle strength and size. Methods: A literature search was conducted in EMBASE, Medline, CINAHL, and CCRCT databases up to 30 January 2022 (osf.io/wdexu; osf.io/ut93s). Data was extracted from all relevant studies and random-effects meta-analyses were completed on studies reporting suitable measures of knee extensors and plantar flexors strength and size. Results: Effect sizes (Hedges’ gav) with 95% confidence intervals for knee extensors strength and size at all durations were -0.80 [-0.92, -0.68] and -0.41 [-0.51, -0.31]. Effects sizes with 95% confidence intervals for plantar flexors strength and size at all durations were -0.68 [-0.89, -0.47] and -0.33 [-0.50, -0.15]. Subgroup analysis resulted in similar effect sizes for knee extensors strength declines for both fixed and mobile knee models at 14 days of disuse. Due to lack of data, no additional analyses were able to be conducted for the potential modulating effects of older age or biological sex. Conclusion: The percentage change of combined effect sizes for declines in skeletal muscle strength and size for the knee extensors and plantar flexors were successfully quantified. Further, a greater amount of single-leg disuse research is needed in populations of older adults and biological females.