Abstract
Age-related changes in the basic functional unit of the neuromuscular system, the motor unit, and its neural inputs have a profound effect on motor function, especially among the expanding number of old (older than ∼60 yr) and very old (older than ∼80 yr) adults. This review presents evidence that age-related changes in motor unit morphology and properties lead to impaired motor performance that includes 1) reduced maximal strength and power, slower contractile velocity, and increased fatigability; and 2) increased variability during and between motor tasks, including decreased force steadiness and increased variability of contraction velocity and torque over repeat contractions. The age-related increase in variability of motor performance with aging appears to involve reduced and more variable synaptic inputs that drive motor neuron activation, fewer and larger motor units, less stable neuromuscular junctions, lower and more variable motor unit action potential discharge rates, and smaller and slower skeletal muscle fibers that coexpress different myosin heavy chain isoforms in the muscle of older adults. Physical activity may modify motor unit properties and function in old men and women, although the effects on variability of motor performance are largely unknown. Many studies are of cross-sectional design, so there is a tremendous opportunity to perform high-impact and longitudinal studies along the continuum of aging that determine 1) the influence and cause of the increased variability with aging on functional performance tasks, and 2) whether lifestyle factors such as physical exercise can minimize this age-related variability in motor performance in the rapidly expanding numbers of very old adults.
Highlights
THE MOTOR UNIT IS THE BASIC functional unit in the neuromuscular system that allows production of force and movement [37]
We focus on the age-related changes in the motor unit and the inputs it receives from spinal and supraspinal sources, and highlight several areas of motor performance that are directly influenced by these changes, including maximal strength and power, velocity of contraction, fatigability, and steadiness during submaximal contractions
Motor performance declines with advanced age and is accelerated in very old age (Ͼ80 yr), involving muscles that are weaker, slower, less powerful, less steady, and more fatigable during high-velocity dynamic tasks
Summary
Contributing factors that interact with biological aging to increase variability between and within old adults includes physical activity, genetics, nutritional status, hormonal status, and inflammatory status among other mediators that will modify the motor unit and motor performance between people as they age and into very old age [27]. Some of this large variability may be exacerbated (or dampened) by the sampling bias associated with cross-sectional design studies that average the motor performance data of subjects over a large age range (60 –90 yr). We focus on the age-related changes in the motor unit and the inputs it receives from spinal and supraspinal sources, and highlight several areas of motor performance that are directly influenced by these changes, including maximal strength and power, velocity of contraction, fatigability, and steadiness during submaximal contractions
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
