Master of Science
Dr. Charles L Rice
Neuromuscular age-related differences of human limb muscles have been widely described with the notable exception of the hamstring muscles. The purpose was to assess contractile function and spinal motor neuron output expressed as motor unit discharge rates in the hamstrings of 11 young (26 ± 4 y) and 10 old (80 ± 5 y) men. Maximal voluntary isometric contractions (MVC), stimulated contractile properties and motor unit discharge rates from sub-maximal to MVC were recorded from the lateral (biceps femoris) and medial (semimembranosus-semitendinosus) posterior thigh. In the old men, knee extension and flexion at MVC were lower (P < 0.05) and voluntary activation as assessed by the twitch interpolation technique was reduced (P < 0.05) compared with the young. Electrically evoked twitches were lower in amplitude and increased in duration of old hamstrings (P < 0.05) compared with the young. At sub-maximal to maximal contraction intensities the old had lower motor unit discharge rates as compared to the young (P < 0.001). At MVC, mean motor unit discharge rates in the biceps femoris and semimembranosus-semitendinosus of old hamstrings were 15.6 ± 6.4 and 15.3 ± 5.9 Hz, as compared to 26.1 ± 10.1 and 27.9 ±7.8 Hz in the young, respectively (P < 0.001). To date, the hamstrings show the greatest age-related reductions in motor unit discharge rates of any major limb muscle. These findings, in relation to motor unit discharge rates from other flexors and extensors support that in ageing, greater reductions are associated with limb flexor muscles.
Kirk, Eric A., "Age-Related Reductions of Motor Unit Discharge Rates in the Human Hamstrings" (2017). Electronic Thesis and Dissertation Repository. 4456.