LOADING RATE IN SELF-INITIATED
VERTICAL JUMP LANDINGS:
DEVELOPMENTAL AND GENDER COMPARISONS

KEY WORDS: landings, loading rate, developmental, gender

INTRODUCTION: Research surrounding the disproportionately higher incidence of non-contact anterior cruciate ligament (ACL) injuries in females, has led to numerous investigations of the biomechanics and neuromuscular aspects of landing (e.g., Lephart, et al., 2002). Among initial findings females had less knee flexion upon landing (McClay, et al., 2001), but current findings are mixed regarding gender differences in landing mechanics (e.g., knee flexion angle) (Fagenbaum, et al., 2003). Few studies have explored when, during development, gender differences may become apparent. This study examined landings across gender and explored when differences might emerge, that is through assessment of gender and developmental (i.e., pre- and post-pubescent) qualities of landing from a self-initiated vertical jump. Although there is no direct causal relationship between magnitude of load and injury, the rate at which vertical load is modulated may be a risk factor for injury. Loading rate information during landing tasks could contribute to the ACL injury puzzle solution (McClay, et al., 2001). Thus, the purpose of this study was to compare gender and developmental differences in vertical loading rate upon landing from a self-initiated vertical jump.

METHODS: Fifty-eight subjects (grouped by age and gender) signed an approved consent to participate. All subjects were recreational participants in jumping and landing activities and demonstrated a mature vertical jump. Motion analysis, force plate, and surface electromyographic data were collected. Fourteen retro-reflective markers provided a 4-segment model for the dominant leg. Each subject jumped to reach a target (i.e., medium sized ball suspended on a retractable cord) then landed in a balanced position with only the dominant foot on the force plate. Loading rate was determined as the maximum vertical ground reaction force (MGRFz) normalized to total body kinetic energy (KE) at initial contact (IC), divided by the time from IC to MGRFz. Data were averaged across 3-4 trials/subject before group means were calculated. A 2 x 2 (gender x development) ANOVA was used to determine significant differences. Significance was set at p < .05.

RESULTS AND DISCUSSION: Results showed significant developmental differences, but no significant gender differences. Pre-pubescent subjects demonstrated greater loading rates (262.7 + 27.8) than post-pubescent subjects (131.9 + 28.3) did, that is, with loading rate normalized to KE at IC to account for differences in body mass and jump height.

REFERENCES:
Fagenbaum, R. & Darling, W.G. (2003). Jump landing strategies in male and female college athletes and the implications of such strategies for anterior cruciate ligament injuries. American Journal of Sports Medicine, 31(2), 233-240.
Lephart, SM, Ferris, CM, Riemann, BL, Myers, JB, & Fu, FH. (2002). Gender differences in strength and lower extremity kinematics during landing. Clinical Orthopaedics and Related Research, 401,162-169.
McClay, I & Ireland, M. ACL research retreat: the gender bias April 6-7, 2001. (2001) Clinical Biomechanics, 16, 937-939.