title: The differential effects of fatigue on reflex response timing and amplitude in males and females.
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 degrees. 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 degrees /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.
authors.affiliation: University of Southern California University Hospital, Los Angeles, CA, USA
authors.forename: Brian D
authors.initials: BD
authors.lastname: Moore
authors.forename: Joshua
authors.initials: J
authors.lastname: Drouin
authors.forename: Bruce M
authors.initials: BM
authors.lastname: Gansneder
authors.forename: Sandra J
authors.initials: SJ
authors.lastname: Shultz
mesh_terms: D000328:Adult; D004576:Electromyography; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000502:physiology*; D008297:Male; D009119:Muscle Contraction; D018763:Muscle Fatigue / Q000502:physiology*; D017847:Patellar Ligament / Q000502:physiology; D012026:Reflex, Stretch / Q000502:physiology*; D012727:Sex Characteristics