A Gender Comparison of Central and Peripheral Neuromuscular Function After Exercise

Authors: Ashley Stern¹, Chris Kuenze², Daniel Herman³, Lindsay D. Sauer⁴, and Joe M. Hart⁴

Affiliations: ¹Department of Human Services, University of Virginia, Charlottesville, VA. ² Department of Kinesiology, University of Virginia, Charlottesville, VA. ³Department of Physical Medicine and Rehabilitation, University of Virginia, Charlottesville, VA. ⁴Orthopaedic Surgery, University of Virginia, Charlottesville, VA.

Acceptance Date: September 19, 2011

Abstract:
Context: Central and peripheral muscle fatigue during exercise may exacerbate neuromuscular factors that increase risk for noncontact anterior cruciate ligament injury. Objective: To compare lower extremity motor evoked potentials (MEPs), muscle strength, and EMG activation after an exercise protocol. Design: Pre-test, Post-test group comparison. Setting: University Laboratory. Participants: Thirty-four healthy volunteers (17 females, age=21.9±2.3 years, weight=77.8±3.0 kg, height=171.1±6.6 cm; and 17 males, age=23.4 ±6.5 years, weight=81.6±3.3 kg, height=179.6±7.3 cm). Intervention: A standardized 30 minute exercise protocol that involved 5 repeated cycles of uphill walking body weight squatting and step-ups. Main Outcome Measures: Quadriceps and hamstring MEP amplitude (mV) and transmission velocity normalized to subject height (m/s) were elicited via transcrianial magnetic stimulation and measured via surface electromyography (EMG). Quadriceps and hamstring peak EMG activation (% MVIC) and peak torque (Nm/kg) were measured during MVICs. Separate ANCOVA’s were used to compare groups following exercise while controlling for baseline measurement. Results: At baseline, males exhibited significantly greater knee extension torques (males=2.47±0.68Nm/kg, Females=1.95±0.53Nm/kg, P=0.036) and significantly higher hamstring MEP amplitudes (males=223.5±134.0mV, Females=89.3±77.6mV, P=0.007). After exercise, males exhibited greater quadriceps MEP amplitude after exercise compared to females (males=127.2±112.7mV, female=32.3±34.9mV, P=0.016). Conclusions: Males experienced greater peripheral neuromuscular changes manifested as more pronounced reductions in quadriceps torque following exercise. Females experienced greater central neuromuscular changes manifested as more pronounced reduction in quadriceps MEP amplitude. Reduced central neural drive of the quadriceps coupled with knee extension torque preservation following exercise may increase risk for knee injury in females.

Keywords: transcranial-magnetic-stimulation, knee-joint, fatigue