The effects of single-leg disuse on skeletal muscle strength and size in the nonimmobilized leg of uninjured adults: a meta-analysis.

The effects of single-leg immobilization on changes in skeletal muscle strength and size in the nonimmobilized leg remain controversial. Some studies have shown decreases, or even increases, in skeletal muscle strength and size of the nonimmobilized leg, thus challenging its role as an internal control. Here, we meta-analyze changes in knee extensor strength and size in the nonimmobilized leg of noninjured adults who participated in single-leg disuse studies. We extracted data from the nonimmobilized leg of participants from 15 of 40 studies included in our previous meta-analysis on single-leg disuse. Single-leg disuse had a trivial effect on knee extensor strength (Hedges' = -0.13 [-0.23, -0.03], < 0.01, -3.6 ± 5.6%, = 13 studies, = 194 participants) and no impact on knee extensor size (0.06 [-0.06, 0.19], = 0.21, 0.8 ± 2.9%, = 9, = 107) in the nonimmobilized leg. By comparison, single-leg disuse had a large effect on knee extensor strength (-0.85 [-1.01, -0.69], < 0.01, -20.4 ± 6.4%; mean difference between legs = 16.8 ± 7.8% [12.8, 20.8], < 0.001) and a medium effect on knee extensor size (-0.40 [-0.55, -0.25], < 0.01, -7.0 ± 4%; mean difference = 7.8 ± 5.6% [11.6, 4.0], < 0.002) in the immobilized leg. These results highlight the utility of the nonimmobilized leg to act as an internal control in single-leg immobilization studies. Our meta-analyses show a trivial effect of single-leg immobilization on leg extensor strength and no effect on leg extensor size in the nonimmobilized leg in uninjured adults. Thus, the nonimmobilized leg in single-leg immobilization studies can serve as useful internal control when examining changes in knee extensor strength and size.