A comparison of knee muscle activation and knee joint stiffness between female dancers and basketball players during drop jumps.

摘要

This dissertation compared knee muscle activation of the lateral gastrocnemius, medial and lateral hamstrings, and lateral quadriceps (LG, MH, LH, and LQ) and knee joint stiffness (KJS) between female dancers (D) and basketball players (B) during the initial landing of a double-leg drop jump. The purpose was to examine possible neuromechanical strategies dancers employ that might protect them from Anterior Cruciate Ligament (ACL) injuries during a potentially high ACL-injury risk activity. Fifty-five females (D=35, 20.7+/-2.3yrs, 164.3+/-6.7cm, 62.2+/-1.9kg, B=20, 20.1+/-2.0yrs, 170.5+/-6.1cm, 72.6+/-11.4kg) performed 5 double-leg drop jumps from a 45cm box. Muscle activity was recorded via surface electromyography (sEMG). A force plate and three-dimensional electromagnetic tracking system were used to record kinetic and kinematic data and calculate KJS (ratio of change in sagittal knee moment to sagittal knee flexion angle from ground contact to maximum knee flexion). sEMG data were normalized to maximum volitional isometric contractions (%MVIC), and joint moments to body weight (Nm/kg). Separate 2x4 ANOVAs compared D and B on muscle onsets (ms) and mean RMS amplitudes (%MVIC) before (PRE=150 ms) and after (POST=50 ms) ground contact. A one-way ANOVA examined group differences in KJS (Nm/kg°), with a stepwise regression model examining prediction of KJS. No significant group differences were observed in muscle onsets (D=133.4+/-53.2ms, B=121.6+/-50.2ms;P=.22), activation amplitudes (PRE: D=28.1+/-8.7%MVIC, B=27.7+/-10.5%MVIC;P=.60; POST: D=51+/-17.3%MVIC, B=49.6+/-21.4%MVIC;P=.78), or KJS (D=.0163+/-.009Nm/kg°, B=.0185+/-.011Nm/kg°;P=.44). Due to recruitment challenges the proposed full complement of participants (N=70;D=35,B=35) was not achieved. Moderate effect sizes (ES) between-groups indicated a trend towards higher muscle activation levels in dancers in MH both pre (34vs.26%MVIC;ES=.55) and post (38vs.25%MVIC;ES=.41) contact, and in LG post contact (45vs.35%MVIC;ES=.33). The exception was LQPOST (90vs.109%MVIC;ES=.30) where dancers had a tendency for lower muscle activation levels. Prelanding muscle activation amplitudes and group membership were not able to predict changes in KJS. These results suggest that the lack of findings may in-part be due to low statistical power. Further, although KJS did not differ between groups, betweengroup effect sizes noted in LG POST, MHPRE, POST, and LQPOST suggest possible differences in neuromechanical strategies over other lower extremity joints. Additional research is necessary to determine possible ACL-injury protective mechanisms employed by dancers during other high ACL-injury risk activities.