Muscular strength and power are correlated with motor unit action potential amplitudes, but not myosin heavy chain isoforms in sedentary males and females. (27th March 2019)

• Record Type: Journal Article
• Authors: Herda, Trent J.; Trevino, Michael A.; Sterczala, Adam J.; Miller, Jonathan D.; Wray, Mandy E.; Dimmick, Hannah L.; Gallagher, Philip M.; Fry, Andrew C.
• Is Part Of: Journal of biomechanics. Volume 86(2019)
• Page Start: 251
• Page End: 255
• Publication Date: 2019-03-27
• Subjects: Motor unit action potential amplitude -- Muscle cross-sectional area -- Isokinetic -- Myosin heavy chain -- Ultrasound -- EMG decomposition; Animal mechanics -- Periodicals; Biomechanics -- Periodicals; Biomechanics -- Periodicals; Mécanique animale -- Périodiques; Biomécanique -- Périodiques; Electronic journals; 571.4305
• DOI: 10.1016/j.jbiomech.2019.01.050
• Languages: English
• ISSNs: 0021-9290

Abstract

Abstract: It remains unclear if the sizes of higher-threshold motor units (MU) are associated with muscular strength and power. Therefore, the purpose of this study was to examine sex-related differences in muscle cross-sectional area (mCSA), percent myosin heavy chain (%MHC) isoform expression, and the MU action potential amplitudes (MUAPAMPS )-recruitment threshold (RT) relationships of the vastus lateralis and isometric peak torque, isokinetic peak torque and mean power at 1.05 rad·s −1 of the leg extensors. Surface electromyographic decomposition techniques were used to quantify MUAPAMPS recorded during isometric muscle actions at 70% of maximal voluntary contractions and regressed against RTs with the slopes calculated. Ultrasound images were used to measure mCSA. Males had greater slopes from the MUAPAMP -RT relationship than the females (P < 0.05). The greater slopes likely reflected larger higher-threshold MUs for the males. The mCSAs and slopes from the relationships were strongly correlated with isometric and isokinetic peak torque and isokinetic mean power (r = 0.78–0.82), however, type I %MHC isoform was only moderately correlated with isometric peak torque (r = −0.54). The results indicated that sex-related differences in muscular strength and power were associated more so with the sizes of the higher-threshold MUs (slopes) and mCSA than MHC isoforms. The amount of cross-bridge activity within muscle fibers that comprise higher-threshold MUs may be the primary contributor to muscular strength and power rather than the contractile properties of the muscle.