Background Female athletic participation has increased over the past decade and with it the prevalence of knee injuries. Current research demonstrates an increased risk of anterior cruciate ligament (ACL) injury for female athletes. However, a number of studies have pointed out that ballet and modern dancers exhibit a lower incidence of ACL injuries despite the fact that they perform jumping and landing frequently.
Objective The objective of this study was to examine how dance experience and instruction affect the lower extremity biomechanics during drop landings. Specifically, lower extremity joint alignment and muscle activation of gluteus maximus and gluteus medius were assessed.
Design Quasi-experimental, cross-sectional
Methods Thirteen active women, 5 dancers and 8 non-dancers, 18-22 years of age, were recruited to participate in this study. In the non-instructed (NI) condition, participants were shown a video demonstrating the drop landing movement in a leg turned out (externally rotated) position. The participants performed the drop landing based on their interpretation of the movement on the video. They were then shown the same video with additional verbal instructions (VI) on how to perform the landing, and asked to perform the same drop landing again. Surface electromyography (EMG) was used to measure muscle activation of the gluteus medius and gluteus maximus during the landings. Kinematics of the lower extremity joints during the deceleration phase of landing were acquired using a digital motion capture system. 2x2 repeated measures ANOVA’s were used to assess the effect of dance experience (dancers and non-dancers) and verbal instruction (NI and VI) on lower extremity biomechanics and gluteal muscle activation.
Results The 2-way ANOVA revealed a significant group by condition interaction with right gluteus medius (p=0.003) and right glut maximus (p=0.009). Dancers showed a significant increase in gluteus medius (p=0.02) while non-dancers showed a significant decrease in gluteus medius (p=0.04) with verbal instruction. Both groups showed significant changes in knee valgus (p\u3c0.001), hip abduction (p=0.027), and hip internal rotation (p=0.031) with verbal instruction. No significant differences were found when comparing those kinematic variables between groups.
Discussion and Conclusion Our results demonstrated that brief verbal instruction has an effect on landing kinematics in college aged women. For both dancer and non-dancers, decreased knee valgus, decreased hip internal rotation, and increased hip abduction were found after verbal instruction was given. In addition, dancers exhibited increased gluteal muscle activation with instruction whereas non-dancers showed a decrease in gluteal muscle activation with instruction. Our findings indicated that explicit movement instruction may result in diminished muscle activation in non-dancers. The heightened awareness of neuromuscular control from dance training may be related to the reduced knee injury risk
