Handgrip strength relates to corticospinal tract microstructure in older adults

Handgrip strength, an indicator of physical frailty, is lower in older age and in females than males, but its neural correlates remain understudied. The present study assessed whether handgrip strength relates to microstructure of the corticospinal tract (CST), a white matter pathway for voluntary motor control that also degrades with age. Healthy older adults (n = 78; 60-87 years) underwent diffusion-weighted magnetic resonance imaging to measure CST microstructure. They also completed three sessions of handgrip squeezes on a dynamometer from which mean, maximum, and variability (standard deviation, coefficient of variation) measures of their maximum voluntary contractions (MVC) were calculated. Analyses replicated effects of age and sex on handgrip strength and CST microstructure. Independent of age and sex, results revealed that better handgrip strength (higher mean and maximum MVC) was related to better CST microstructure (higher intracellular, lower mean diffusivity). Finding that the CST is a neural correlate of handgrip strength suggests that its degradation may be a marker of physical frailty in older adults.