The Effects of a Game Simulation on Muscle Activation and Knee Kinematics in Females

Intro: Female athletes experience non-contact ACL injuries at 5 times the rate of male athletes. These injuries occur more frequently at the end of halves and may be associated with exercise-induced fatigue causing knee instability. The purpose of this pilot study was to determine the effect of strenuous exercise on lateral knee movement during the landing phase of a jump. Methods: Ten subjects completed both the exercise and the control trial consisting of two 25-min game simulations on a treadmill or on a separate day the equivalent rest. Before, at half time, and immediately following the interventions subjects performed sets of 3 box jumps and vertical leaps. Surface Electromyography (sEMG) was used to assess relative muscle activation (%MVIC) and 2D video analysis to assess changes in Q Angle upon landing from a box jump. Data were analyzed by 2 factor repeated measures ANOVA. Results: Power analysis indicated the study was under powered and that 18 subjects were necessary to be adequate statistical power; therefore, results were interpreted with p≤0.1 as significant. There was no effect of exercise on Vertical leap, a measure of muscular fatigue. However, Q angle increased by 7.4 degrees following completion of the second exercise session (Pre:21.7±2.34 vs Post: 29.2±5.48) (p=.09). %MVIC decreased significantly over time for the Gastrocnemius (Pre: 78%±4% vs Post: 66%± 5%, p≤.1), bicep femoris (Pre: 68%± 3% vs Post: 64%±3%, p≤.05) and gluteus medius (Pre: 72%±5% vs Post: 58%±4%, p≤.05). The latissimus dorsi (Pre: 48%±2% vs Post: 41%±3%, p≤.05) and gluteus medius (Pre: 34%±3% vs Post: 29%±2%, p≤.05) muscles were activated later when comparing pre-exercise values to post-exercise results. Conclusion: These data indicate that knee instability with exercise may not require muscular fatigue, and that changes are associated with altered muscle activation. The changes in muscle activation timing may reflect compensation for altered muscle activation