A pilot study on aging-related effects on step performance: The role of muscle quality, size, and strength

Older adults experience a high risk of falls, often due to impaired stepping responses that require rapid and efficient weight transfer. This pilot study examined whether age group and principal component analysis (PCA)-derived profiles of muscle morphology, muscle quality, and strength were associated with weight-transfer performance during voluntary forward and backward stepping. Twenty-three younger and older adults underwent ultrasound imaging of the tensor fasciae latae (TFL), vastus lateralis (VL), and biceps femoris (BF), assessments of knee extensor, knee flexor, and hip abductor strength, and completion of a Choice Reactive Stepping Test (CRST). PCA was applied to nine muscle-related variables to summarize interrelated measures of muscle size, echo intensity, and strength into neuromuscular profiles. The first four principal components (PCs) explained approximately 80.8% of the total variance. PC1 reflected a favorable muscle quality and strength profile, characterized by lower echo intensity and greater hip abduction and knee flexion strength. PC2 suggested a dissociation between TFL thickness and force-generating capacity, whereas PC3 and PC4 reflected muscle-specific structural and strength heterogeneity. PCA-derived PC scores and age group were then entered into a multivariate multiple regression (MMR) model, with weight-transfer onset (WTO) and weight-transfer duration (WTD) during forward and backward stepping as response variables. The MMR model did not provide statistical evidence that age group or any PC was associated with the combined WTO and WTD outcomes. These findings suggest that, in this sample, resting muscle morphology, muscle quality, and maximal strength did not explain weight-transfer performance when modeled as integrated neuromuscular profiles. Weight-transfer performance during stepping may depend on dynamic neuromuscular factors, such as rapid force generation, activation timing, coordination, and task-specific balance strategies, which should be examined in larger studies.