Author(s): SHOJI, K., SHIOUCHI, M., MANABE, Y., Institution: CHUKYO UNIVERSITY, Country: JAPAN, Abstract-ID: 2035

INTRODUCTION:
Deadlift performance requires high hip extension torque while maintaining lumbar stability, and insufficient control of lumbar alignment may increase spinal loading and injury risk. Previous studies have shown that lumbar lordosis angle (LLA) decreases as load increases. However, whether load-dependent reductions in LLA are associated with hip extension torque remains unclear. The aim of this study was to examine the relationship between LLA displacement and hip extension torque during deadlifts performed at 60% and 90% of one-repetition maximum (1RM).
METHODS:
Twelve healthy young male participants performed deadlifts at 60% and 90%1RM. Three-dimensional kinematic data were collected using an optical motion capture system (VICON MX). Six reflective markers were placed on selected spinous processes to construct a sagittal-plane trunk model consisting of six rigid segments. Hip extension torque was separately assessed using an isometric dynamometer (CONTREX MJ). Trunk kinematics and joint kinetics were calculated using two-dimensional inverse dynamics in MATLAB (MathWorks).
RESULTS:
The minimum LLA during deadlift was 165.6 ± 6.5° at 60% 1RM and 161.6 ± 6.9° at 90% 1RM (P<0.05). The angular displacement from neutral (T-pose) to minimum LLA increased by 4.0 ± 2.3° with increasing load. Maximum hip extension torque was 388.3 ± 47.7 Nm (5.4 ± 0.6 Nm/kg). A non-significant correlation was found between 1RM (1RM/kg) and LLA displacement (R² = 0.05). A significant negative correlation was found between maximum hip extension torque and LLA displacement (R² = 0.63).
CONCLUSION:
Therefore, increased lumbar flexion was not explained by the magnitude of 1RM, but was suggested to be associated with maximal hip extension torque capacity. These findings suggest that lumbar alignment during high-load deadlift may reflect the balance between hip extension torque and trunk stabilization demands.