The differential effects of fatigue on reflex response timing and amplitude in males and females

Brian D Moore,Joshua Drouin,Bruce M Gansneder,Sandra J Shultz

doi:10.1016/s1050-6411(02)00032-9

Abstract

We examined the effects of fatigue on patellar tendon reflex responses in males and females. A spring-loaded reflex hammer elicited a standardized tendon tap with the knee positioned in an isokinetic dynamometer and flexed to 85°. We recorded vastus lateralis activity (SEMG) and knee extension force production at the distal tibia (force transducer). Reflex trials were performed before and after (immediate, 2, 4, and 6 min) an isokinetic fatigue protocol to 50% MVC (90°/s). For each event, pre-motor time (PMT), electromechanical delay (EMD), and total motor time (TMT) were obtained, as well as EMG amplitude (EMG amp), time to peak EMG (EMG tpk), peak force amplitude (F amp), time to peak force (F tpk), EMG:force ratio (E:F), and rate of force production (F rate=N/ms). TMT increased significantly in females following fatigue, while males showed no change. The increased TMT was due to an increased EMD with fatigue, while PMT was unaffected. EMG amp and F amp were somewhat diminished in females yet significantly augmented in males following fatigue, likely accounting for the differential changes in EMD noted. Results suggest males and females may respond differently to isokinetic fatigue, with males having a greater capacity to compensate for contraction force failure when responding to mechanical perturbations.

Highlights

With the increased participation of females in team sports over the past decade, a dramatic increase in the rate of knee injuries involving the anterior cruciate ligament (ACL) has been documented [2], [16], [34] and [45]
After confirming that the rate of fatigue was similar in males and females, we found total motor time (TMT) to differ within trials (p
We found no change in TMT for males at any time point, and no difference between males and females at 2, 4 and 6 min of the recovery period

Summary

Introduction

With the increased participation of females in team sports over the past decade, a dramatic increase in the rate of knee injuries involving the anterior cruciate ligament (ACL) has been documented [2], [16], [34] and [45]. A gender discrepancy in ACL injury rates seems to be most prominent in sports requiring intense cutting, jumping, and rapid change-of-direction movements [14]. This gender-bias in ACL injury rate has led to many studies attempting to elicit physiological, hormonal, and anatomical variances that may predispose females to ACL injury [35], [38], [44], [47], [60] and [61]. The hamstring muscles in particular provide dynamic protection to the ACL by limiting anterior tibial translation [46] and [51]. Co-contraction of the quadriceps and hamstring muscle groups effectively stiffens the joint [4], [36] and [46], which is instrumental when movement precision and joint stabilization are critical [31]

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