Knee muscular response strategies differ by developmental level but not gender during jump landing.
The purpose of this investigation was to determine differences between pre- and post-pubescent males and females in quadriceps (vastus medialis; VM) and hamstrings (medial hamstrings and biceps femoris; HAMS) muscular activation patterns via the root mean square of surface electromyography (SEMG) during self-initiated vertical jump landing. Fifty-eight subjects, divided into age and gender groupings, were compared on kinematic variables during pre-landing (100 msec preceeding initial ground contact), post-landing (100 msec following initial ground contact), and initial-contact-to-maximum-knee-flexion stages. Kinematic variables investigated were (1) SEMG values during each stage of the vertical-jump landing; (2) Co-contraction ratios (CCR), which represented the ratio of normalized hamstrings' activity to normalized quadriceps' activity; and, (3) knee angle at initial contact. Results indicated (1) no significant gender differences in variables measured; and, (2) significant developmental level differences. Post-pubescent subjects displayed greater HAMS acitivity and CCR values in the pre-landing stage relative to post-landing stages, indicating that post-pubescent subjects had a greater level of hamstrings co-contraction prior to landing than pre-pubescent subjects. Conversely, pre-pubescent subjects displayed greater post-landing and initial-contact-to-maximum-knee-flexion ratios, indicating a greater level of hamstrings' co-contraction during post-landing stages than post-pubescent subjects. There were no significant differences in knee angle at initial contact. The greater level of hamstrings' co-activation prior to landing by post-pubescent subjects indicated that they used a strategy of pre-tuning the hamstrings prior to landing (more CNS pre-activation) to control the ground reaction forces and anterior tibial displacement experienced by the knee during landing. On the other hand, pre-pubescent subjects controlled these forces by having a greater level of hamstrings' co-activation during landing, which represents more of a reflexive activation in response to ground impact.
University of New Hampshire's Applied Biomechanics and Motor Control Laboratory, Department of Kinesiology, Durham, NH 03824, USA. rvc@cisunix.unh.edu
R V
RV
Croce
P J
PJ
Russell
E E
EE
Swartz
L C
LC
Decoster
D000328:Adult; D000367:Age Factors; D002648:Child; D004576:Electromyography; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000502:physiology*; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D012018:Reflex / Q000502:physiology; D012737:Sex Factors