Reduced Neural Excitability and Activation Contribute to Clinically Meaningful Weakness in Older Adults.
Level 4 - case-series / case-control
Cross-sectional comparative observational study
PubMed 32588058 · doi:10.1093/gerona/glaa157
What was done
In 66 older adults (aged 75.1 ± 7.0 years) and 20 young adults (aged 22.0 ± 1.9 years), researchers measured leg extensor strength, thigh lean mass, voluntary inactivation (VIA), motor evoked potential (MEP) amplitude, and silent period (SP) duration. Older adults were classified into Weak, Modestly Weak, or Not Weak subgroups based on strength-to-body-weight thresholds. Regression analyses evaluated the relative contributions of neural excitability variables and thigh lean mass to strength variance.
What was found
Older adults had 63% less strength per body weight than young adults. Weak older adults had significantly higher voluntary inactivation than Not Weak older adults (14.2 ± 7.5% vs 6.1 ± 7.5%) and MEP amplitudes that were half as large. Weak older adults had 24% longer silent periods than Not Weak older adults, which did not reach statistical significance (p = .06). Regression analysis showed MEP amplitude, SP duration, and thigh lean mass together explained ~62% of the variance in leg extensor strength, with neural excitability variables explaining ~33% and thigh lean mass explaining ~29%.
Why it matters
These findings suggest that impairments in corticospinal excitability and voluntary activation contribute as much to late-life weakness as muscle mass loss, supporting neural targets for intervention.
Limits
The study is cross-sectional, precluding causal conclusions. The total sample size is small (n = 86 across all groups), subgroup sizes are not reported, and the silent period difference did not achieve statistical significance (p = .06).
Cited by
- supports During aging, the loss of muscle strength is greater than can be explained solely by the loss of muscle mass.