(28) SEX AND LOAD BASED NEUROMUSCULAR LOADING DURING SUBMAXIMAL BACK SQUATS

Intro: Despite its frequent prescription across both sexes, males and females perform loaded back squats differently. Males exhibit smaller hip flexion and greater knee flexion angles during squats compared to females, indicating different movement strategies possibly due to altered muscle activation. In addition to neuromuscular assessments like quadricep to hamstring ratios (which are pertinent across many dynamic tasks), multifaceted variables like joint work, which represents the summative load placed on the joints to perform a task, could shed light on neuromechanical differences between males and females, and provide foundation for improving programming.

Purpose: The purpose of this study is to investigate sex differences in hip and knee joint work and integrated muscle activation (EMG) across two submaximal loads.

Methods: 17 healthy adults (8 females) with at least six months of experience squatting with appropriate technique completed this two day study. One repetition max (1RM) was tested on day one and used to calculate the submaximal loads on day two. Five squats were performed to full (120-degree knee flexion) depth at 50% 1RM, and 80% 1RM. Lower body kinematics (Vicon Vantage System; 200Hz), kinetics (Bertec forceplates; 2000Hz), and EMG (Delsys Trigno; 2000Hz) were recorded for all squats. Joint work (Joules/system mass) was calculated for the downward (beginning of descent to full depth) and upward (full depth to standing upright) phases separately. Integrated quadricep to hamstring activation ratio (semitendinosus, biceps femoris, vastus lateralis and vastus medialis) was determined across the full squat. Two-way mixed model analyses of variance were used to determine sex by load interactions and main effects. RESULTS: No significant interactions were found for any variable (p >0.05; Table 1). No sex main effects were found in knee joint work (p >0.05). However, there was a sex main effect in hip joint work for both the eccentric (partial eta^2 effect size: η_p² = 0.343) and the concentric (η_p² = 0.277) phases, with women displaying greater work than men. There were significant load main effects, with 80% 1RM loads invoking larger work than 50% 1RM loads for both hip and knee eccentric (η_p² =0.264 & η_p² = 0.481, respectively) and concentric (η_p² =0.277 & η_p² =0.653, respectively) phases.

Conclusions: The significant increase in hip joint work for females compared to males and across loads provides evidence to include more full depth back squat movements for female athletes to improve hip strength and decrease the knee dominance currently found in female athletes during dynamic eccentric tasks like landing. Future research should aim to expand on this work by, assessing different depths (e.g., parallel), stance width, bar position, and shoe type. PRACTICAL APPLICATION: Strength and conditioning coaches should consider implementing more full depth squat to enhance hip loading in female athletes.

Acknowledgements: None