Abstract

The number of injuries sustained by female athletes has been on the rise. Female athletes are 4 to 8 times more at risk of suffering an anterior cruciate ligament injury (ACL). Strength is believed to be an important predictor of ACL injury in female athletes and has been a focus of improvement in injury prevention programs. However, there is a lack of consensus on the relationship between muscle strength and hip and knee kinematics during landing tasks. Only a few studies used a lower extremity relative strength measure and reported promising results, but none of them reported EMG activity. The goal of this study was to explore the relationship between back squat strength to body mass ratio and the lower limb muscle activity during single-leg landing tasks.

Twenty-eight varsity athletes were recruited (13 males and 15 females) from various sports from the universities in the Montreal, Québec region. Participants were asked to perform a standardized 1-RM back squat test followed by single-leg drop landings from 28cm and 44cm plyometric boxes. EMG data was collected 150ms pre-initial and 250ms post-initial contact for the following muscles: biceps femoris (BF), semitendinosus (ST), vatus lateralis (VL), vastus medialis (VMO), rectus femoris (RF), gluteus medius (GMED) and gluteus maximus (GMAX). Significant differences were found between male and female athletes on the back squat one-repetition maximum and squat to body mass ratio (SQ:BW). Females had significantly more neuromuscular activity of the quadriceps and GMAX, and significantly less activity of the biceps femoris in both landing phases. After controlling for strength, only significant differences in RF, BF and GMAX activity remained between sexes in the deceleration phase. Prior to landing, moderate negative correlations between VL, VMO and GMAX activity and SQ:BW were observed at both drop heights. During the post-initial contact phase, moderate negative correlations for VL and VMO activity were found at both drop heights. Our findings suggest that researchers looking at sex-based differences in muscle activity should control for relative strength differences between groups as it may influence muscle activity during landing tasks.