Covert age-related differences in agility are related to both muscle strength and integrity of the corticospinal tract

Abstract

Background: Agility involves moving efficiently without losing balance, requiring muscular strength and neuromuscular capacity. Maintaining agility promotes aging with vitality, living without frailty, and reduced fear of falling. Factors that influence age-related differences in agility are unknown. Methods: Participants were recruited to determine whether quadriceps strength or integrity of the corticospinal tract (CST) influenced age-related differences in agility. Participants underwent Transcranial Magnetic Stimulation to measure CST integrity and completed a lower limb agility hopping task. CST excitability was calculated as active motor threshold intensity, the lowest stimulator output that produced a motor evoked potential. We used regression modelling to predict the contribution of quadriceps strength and CST integrity to lower limb agility, when controlling for sex. Results: Greater quadriceps strength correlated with longer hop length (r = .581,p <.001) and reduced hop length variability (r=-.384,p=.039). Lower active motor threshold correlated with longer hop length (r=-.364,p=.048) and reduced hop length variability (r=.478,p=.007). Decreased quadriceps strength significantly predicted shorter hop length (R²=.393,p=.002) while higher active motor threshold predicted greater hop variability (R²=.182,p=.036). Conclusions: Agility involves a combination of muscle power and coordination, which can be tested with a hopping agility task. CST integrity predicted coordination on the task, but not strength, even when controlling for sex.