Nerve, muscle and adiposity: Associations with gait speed across adulthood in the Baltimore Longitudinal Study of Aging.

Multivariable regression explained 29% and 40% of the variance in usual and rapid gait speed, respectively.

• Study included 898 participants from the Baltimore Longitudinal Study of Aging (BLSA), aged ≥20 years.
• Participants had complete data on gait speed, body composition, muscle cross-sectional area (MCSA), intramuscular fat (IMAT), and peripheral nerve function.
• Both usual and rapid gait speed were modeled using multivariable regression with the same set of predictors.

Peripheral nerve measures (signal amplitude and conduction velocity) showed modest associations with both usual and rapid gait speed after mutual adjustment.

• Peripheral nerve function was assessed via signal amplitude and conduction velocity.
• Associations were present after adjusting for other variables including age, height, body roundness index, MCSA, and IMAT.
• The associations were described as 'modest,' indicating a statistically significant but relatively small effect size.

Age, height, body roundness index (BRI), MCSA, and IMAT were independently associated with both usual and rapid gait speed.

• These variables were independently associated after mutual adjustment in multivariable regression models.
• Both muscle morphology measures (MCSA and IMAT) and body composition measures (BRI, height) contributed independently to gait speed.
• The independence of these associations was established after including peripheral nerve function measures in the same models.

Structural equation modelling identified MCSA and IMAT as the primary mediators of age-related gait decline, while nerve function played a smaller, task-specific role.

• Structural equation modelling was used to evaluate mediation pathways linking age to gait speed.
• MCSA (muscle cross-sectional area) and IMAT (intramuscular fat) were identified as dominant mediators.
• Nerve function mediation was described as 'smaller' and 'task-specific,' suggesting differential contributions to usual versus rapid gait.

Multi-group analysis revealed that the physiological mechanisms underlying gait were stable across adulthood, but the direct effect of age on rapid gait attenuated in the oldest-old.

• Multi-group structural equation modelling was used to assess whether mechanisms differed by age group.
• Mechanisms were found to be stable across adulthood in the broader sample.
• In the oldest-old subgroup, the direct effect of age on rapid gait was attenuated, indicating that functional decline in this cohort is fully mediated by neuromuscular and morphological factors.