Changes in the flexion-relaxation response induced by hip extensor and erector spinae muscle fatigue.
BACKGROUND
The flexion-relaxation phenomenon (FRP) is defined by reduced lumbar erector spinae (ES) muscle myoelectric activity during full trunk flexion. The objectives of this study were to quantify the effect of hip and back extensor muscle fatigue on FRP parameters and lumbopelvic kinematics.


METHODS
Twenty-seven healthy adults performed flexion-extension tasks under 4 different experimental conditions: no fatigue/no load, no fatigue/load, fatigue/no load, and fatigue/load. Total flexion angle corresponding to the onset and cessation of myoelectric silence, hip flexion angle, lumbar flexion angle and maximal trunk flexion angle were compared across different experimental conditions by 2 x 2 (Load x Fatigue) repeated-measures ANOVA.


RESULTS
The angle corresponding to the ES onset of myoelectric silence was reduced after the fatigue task, and loading the spine decreased the lumbar contribution to motion compared to the hip during both flexion and extension. A relative increment of lumbar spine motion compared to pelvic motion was also observed in fatigue conditions.


CONCLUSIONS
Previous results suggested that ES muscles, in a state of fatigue, are unable to provide sufficient segmental stabilization. The present findings indicate that, changes in lumbar-stabilizing mechanisms in the presence of muscle fatigue seem to be caused by modulation of lumbopelvic kinematics.
Descarreaux
Martin
M
Département de chiropratique, Université du Québec à Trois-Rivières, Trois-Rivières G9A 5H7, Canada. martin.descarreaux@uqtr.ca
Lafond
Danik
D
Cantin
Vincent
V
D000328:Adult; D001696:Biomechanical Phenomena / Q000502:physiology; D005260:Female; D006621:Hip Joint / Q000502:physiology*; D006801:Humans; D008159:Lumbar Vertebrae / Q000033:anatomy & histology / Q000502:physiology*; D008297:Male; D009068:Movement / Q000502:physiology; D009119:Muscle Contraction / Q000502:physiology; D018763:Muscle Fatigue / Q000502:physiology*; D009126:Muscle Relaxation / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology*; D004856:Postural Balance / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology; D012018:Reflex / Q000502:physiology; D016474:Weight-Bearing / Q000502:physiology; D055815:Young Adult