Comparisons Of Lumbosacral Joint Angles And Moments By Sex In Stiff-leg Deadlift

BACKGROUND: The stiff-leg deadlift (SLDL) is a form of resistance training, commonly performed by physically active people. However, the role sex (male or female) plays in lumbosacral (L5-S1) joint mechanics during SLDL is not well understood. PURPOSE: To examine the effect of sex on L5-S1 mechanics during SLDL. METHODS: A cross-sectional, controlled laboratory study design was used. Physically active young adults performed SLDL using four different loads (0%, 40%, 60%, and 80%) based on their one repetition maximum (1RM) weights, which were captured by a marker-based three-dimensional motion analysis system (120 fps) and force plates (1200 Hz). The SLDL was separated into descending and ascending phases. Peak angles (degrees) at the beginning of the ascending phase and peak internal joint moments normalized to body mass (Nm/kg) at the L5-S1 during the descending and ascending phases were compared by sex in different loads. Mann-Whitney U test with p < 0.05 was used for analysis. RESULTS: Twenty-five young adults (11 males and 14 females, age: 26.2 ± 4.7 years) participated. Mean weight training experiences was 6.9 ± 5.0 years, and 86% of them were currently training. No sex differences at L5-S1 joint angle were detected at baseline, static measures (p = 0.993) prior to the SLDL performance. Mean peak flexion angles of the L5-S1 were greater in females than males at 0% (15.4 ± 14.7 vs. 6.8 ± 7.3 degrees, p = 0.033) and 40% (18.6 ± 15.8 vs. 6.9 ± 10.3 degrees, p = 0.031), but not at 60% (p = 0.066) and at 80% (p = 0.051). Mean peak body mass normalized flexion moments of the L5-S1 were consistently higher in males than females in both descending (40%: 2.3 ± 0.7 vs. 1.3 ± 0.3 Nm/kg, p < 0.001; 60%: 3.1 ± 1.0 vs. 1.9 ± 0.4 Nm/kg, p < 0.001; 80%: 3.8 ± 0.8 vs. 2.4 ± 0.6 Nm/kg, p = 0.003) and ascending (40%: 2.5 ± 0.7 vs. 1.4 ± 0.4 Nm/kg, p < 0.001; 60%: 3.5 ± 0.9 vs. 2.1 ± 0.6 Nm/kg, p < 0.001; 80%: 4.3 ± 0.8 vs. 2.7 ± 0.7 Nm/kg, p = 0.002) phases except for 0% in both descending (p = 0.341) and ascending (p = 0.472). CONCLUSIONS: There were sex differences in flexion angles and moments of the L5-S1 while performing SLDL. Greater L5-S1 flexion angles experienced by females and flexion moments experienced by males may help further our understanding of SLDL biomechanics and enhance clinical implications, including providing a safe instruction aiming to prevent low back injuries.