Motor function: measurement, translation and the effects of age

Motor function encompasses the capacity of the nervous system to control the actions of muscles to exert forces and thereby produce movement. Motor function can be characterized by performance on such subdomains as locomotion, strength, dexterity, balance, endurance, steadiness, and performance fatigability. The measurement techniques used to assess these domains vary depending on the neuromuscular property being assessed, the species being investigated, and the age of the person or animal. The four projects in this dissertation examined the measurement of motor function and its modulation by age. The first study focused on the motor domain of performance fatigability in humans, and found that endurance time depends on the compliance of the load and also the rate of increase in muscle activation. The second study examined the influence of age on performance fatigability and found that, contrary to previously published works, fatigability of the dorsiflexor muscles is greater in older adults. The third study assessed the influence of metabolic biomarkers on motor function in older adults, and found that vitamin D hormone and fasting insulin are associated with walking endurance in relatively healthy older men and women. The fourth study developed a mouse model of multiple domains of motor function to further assess the influence of age on motor function. Taken together, these results reinforce the importance of assessing of multiple tasks and subdomains when characterizing motor function with advancing age in people and animals