The Influence of Motor Unit Number and Muscle Activation on Early Phase Rate of Torque Development in Younger and Older Men

Abstract

This study examined the influence of muscle activation and motor unit number estimation (MUNE) on early phase voluntary rate of torque development (RTD) in younger (YM) and older (OM) men. Thirty-two YM (n = 17; Age = 22 yrs) and OM (n = 15; Age = 74 yrs) volunteered to participate in this study. Early phase RTD (first 50 ms of a rapid isometric contraction; RTD₅₀) and normalized surface electromyography (first 50 ms of muscle excitation; nEMG₅₀) were recorded from the right quadricep muscle group. MUNE was examined from the right vastus lateralis. Multiple linear regression analyses revealed that nEMG₅₀ had a significant effect on RTD₅₀ independent of age group (p ≤ 0.001). nEMG₅₀ had a significant effect on RTD₅₀ in the OM group (p = 0.037). MUNE had no effect on RTD₅₀ independent of age. Older adults may depend more on muscle activation at contraction onset of early phase RTD compared to younger adults.

Keywords:

• Aging
• neuromuscular
• quadriceps
• electromyography

Disclosure statement

No potential conflict of interest was reported by the authors.

Ethics Approval

This study was approved by the University’s Institutional Review Board (IRB# ED-18-75). All procedures performed in this study were in accordance with the 1964 Helsinki declaration and its later amendments.

Additional information

Funding

This work was partially supported by the Central States American College of Sports Medicine research Grant and the Oklahoma State University Graduate College’s Robberson Summer Dissertation Fellowship Grant. Both grants were awarded to M.A.M. Neither of the financial sponsors engage in the design, execution, analysis, interpretation or writing of the study.