Skeletal muscle disuse. Caution for those with high baseline values

📖 Literature Information and Abstract Translation

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

[Background/Objective] We aimed to evaluate the effects of muscle disuse on muscle strength (MS), muscle mass (MM), and cardiovascular fitness.

[Methods] We searched databases to identify human studies evaluating the effects of muscle disuse on (1) MM, (2) maximal oxygen uptake (VO2max), and/or MS. Random-effects meta-analysis and meta-regression were performed, with baseline fitness and protocol duration as a priori determined moderators. 51 different studies were quantitatively analyzed, with a significance level set at p<0.05.

[Results] Data from participants in 14 studies showed declines in both VO2max (SMD: -0.93; 95% CI: -1.27 to -0.58) and MM (SMD: -0.34; 95% CI: -0.57 to -0.10). Data from 47 studies showed declines in muscle strength (-0.88; 95% CI: -1.04 to -0.73) and mass (SMD: -0.47; 95% CI: -0.58 to -0.36).

■ Skeletal muscle disuse ①: Muscle mass loss × Muscle strength loss
・The decrease in MS was twice that of the decrease in MM, but there were differences depending on the anatomical site.
・Data for the upper arm (●) shows a nearly horizontal regression line, indicating that changes in muscle mass have little effect on the decline in muscle strength.
・The lower leg (▲) has a regression line with a steep slope, indicating a tendency for muscle mass to decrease significantly in response to muscle strength loss.
・The thigh (■) also shows a decrease in muscle mass in response to muscle strength loss, but this tendency is more gradual than in the lower leg.

■ Skeletal muscle disuse ②: Baseline muscle strength × Muscle strength loss
・There is a tendency for the amount of muscle strength loss to be greater as baseline muscle strength is higher (negative correlation).
・For example, subjects with a baseline muscle strength of approximately 150 Nm show a muscle strength loss of about -20 Nm, whereas subjects with a baseline muscle strength of approximately 300 Nm reach a muscle strength loss of -80 Nm to -100 Nm.

■ Skeletal muscle disuse ③: Baseline muscle mass × Muscle mass loss
・There is a tendency for the decrease in muscle volume to be greater as the baseline quadriceps volume is larger.
・For example, subjects with a baseline volume of about 1000 mL show a volume decrease of about -50 mL, whereas subjects with a baseline volume exceeding 2000 mL reach a volume decrease of about -150 mL to -200 mL.

[Conclusion] It was reported that muscle strength loss is more severe in subjects with higher muscle strength. This is physiologically significant for athletes. However, it should be noted that for elderly individuals with low muscle strength, a period of muscle disuse can have devastating consequences.

🌱 So What?: What did I find interesting?

“Nobishiro” (room for growth) is a common term.

As shown above, it is a word used to describe potential in a positive direction.
In the study reviewed this time, conversely, it became clear that in skeletal muscle disuse, the higher the baseline values of muscle strength and muscle mass, the greater the “sagishiro” (room for decline).
When a medium-to-long-term period of disuse is predicted and baseline values are high, caution is required because the “room for decline” of skeletal muscle disuse is large.

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