Single‐leg disuse decreases skeletal muscle strength, size, and power in uninjured adults: A systematic review and meta‐analysis

Abstract

We aimed to quantify declines from baseline in lower limb skeletal muscle size and strength of uninjured adults following single‐leg disuse. We searched EMBASE, Medline, CINAHL, and CCRCT up to 30 January 2022. Studies were included in the systematic review if they (1) recruited uninjured participants; (2) were an original experimental study; (3) employed a single‐leg disuse model; and (4) reported muscle strength, size, or power data following a period of single‐leg disuse for at least one group without a countermeasure. Studies were excluded if they (1) did not meet all inclusion criteria; (2) were not in English; (3) reported previously published muscle strength, size, or power data; or (4) could not be sourced from two different libraries, repeated online searches, and the authors. We used the Cochrane Risk of Bias Assessment Tool to assess risk of bias. We then performed random‐effects meta‐analyses on studies reporting measures of leg extension strength and extensor size. Our search revealed 6548 studies, and 86 were included in our systematic review. Data from 35 and 20 studies were then included in the meta‐analyses for measures of leg extensor strength and size, respectively (40 different studies). No meta‐analysis for muscle power was performed due to insufficient homogenous data. Effect sizes (Hedges' gav) with 95% confidence intervals for leg extensor strength were all durations = −0.80 [−0.92, −0.68] (n = 429 participants; n = 68 aged 40 years or older; n ≥ 78 females); ≤7 days of disuse = −0.57 [−0.75, −0.40] (n = 151); >7 days and ≤14 days = −0.93 [−1.12, −0.74] (n = 206); and >14 days = −0.95 [−1.20, −0.70] (n = 72). Effect sizes for measures of leg extensor size were all durations = −0.41 [−0.51, −0.31] (n = 233; n = 32 aged 40 years or older; n ≥ 42 females); ≤7 days = −0.26 [−0.36, −0.16] (n = 84); >7 days and ≤14 days = −0.49 [−0.67, −0.30] (n = 102); and >14 days = −0.52 [−0.74, −0.30] (n = 47). Decreases in leg extensor strength (cast: −0.94 [−1.30, −0.59] (n = 73); brace: −0.90 [−1.18, −0.63] (n = 106)) and size (cast: −0.61[−0.87, −0.35] (n = 41); brace: (−0.48 [−1.04, 0.07] (n = 41)) following 14 days of disuse did not differ for cast and brace disuse models. Single‐leg disuse in adults resulted in a decline in leg extensor strength and size that reached a nadir beyond 14 days. Bracing and casting led to similar declines in leg extensor strength and size following 14 days of disuse. Studies including females and males and adults over 40 years of age are lacking.

The role of muscle disuse in muscular and cardiovascular fitness: A systematic review and meta‐regression

“…Therefore, the absence of differences in MS loss between older and younger individuals in our study could be attributed to the lack of physical tests involving explosive strength. The lack of muscle power‐related outcomes has also been reported when examining the knee extensors in response to immobilization (Preobrazenski et al., 2023). We recommend that future studies assessing muscle disuse include data on power strength.…”

“…A recent systematic review and meta‐analysis by Preobrazenski et al. (2023) quantified changes in MS and MM in the knee extensors following single‐leg immobilization. The study reported that declines in MS and MM tend to plateau after 14 days of disuse.…”

Pathophysiological mechanisms of reduced physical activity: Insights from the human step reduction model and animal analogues

“…80 These conflicting results contrast with the wellestablished marked loss of muscle strength with disuse, which is estimated, following a 2-week intervention, to be 13% for bed rest, 108 14% for unilateral lower limb suspension, 101 and 23% for unilateral lower limb immobilisation. 111 Cardiorespiratory fitness declines with 2-week SR are 3.4%-6.4% in young adults 20,74,75 and 6.5% in older adults 71 and are contained compared with what was observed in a bed rest study of the same duration (young adults: −7.6%; older adults: −15.3%). 112 Differently, declines in insulin sensitivity assessed with the Matsuda index seem similar between SR (−17.6% to 22%) 73,78 and bed rest (−19.8%) 112 in healthy older adults over 2 weeks of intervention.…”

“…Changes in knee extensors isometric muscle force with 2‐week SR are trivial, ranging from +2.8% (non‐significant increase) 79 to −7.1% 80 . These conflicting results contrast with the well‐established marked loss of muscle strength with disuse, which is estimated, following a 2‐week intervention, to be 13% for bed rest, 108 14% for unilateral lower limb suspension, 101 and 23% for unilateral lower limb immobilisation 111 . Cardiorespiratory fitness declines with 2‐week SR are 3.4%–6.4% in young adults 20,74,75 and 6.5% in older adults 71 and are contained compared with what was observed in a bed rest study of the same duration (young adults: −7.6%; older adults: −15.3%) 112 .…”

Short‐term disuse does not affect postabsorptive or postprandial muscle protein fractional breakdown rates

“…The leg randomized to undergo immobilization (IMM) was counterbalanced within each group for leg dominance, while the contralateral leg served as a free‐living, within‐subject control (CON). It is well established that muscle volume and/or cross‐sectional area of the non‐immobilized control leg remains unchanged during one‐legged knee immobilization lasting 2–14 days, 12,18,26–28 suggesting that muscle protein net balance is unaltered, making this an appropriate internal control. With the IMM knee immobilized at 70° flexion (full knee extension considered as 0°; see supporting information), participants were instructed how to use crutches and asked to refrain from bearing any weight on the immobilized leg, as well as to refrain from alcohol and strenuous exercise during immobilization.…”