Impact of gender, posture and phase on back and lower extremity moments and muscle excitation during lifting task: a cross-sectional study.

Purpose: The aim of this work was to investigate and compare back and lower extremity joint moments and muscle excitation during stoop and squat postures by incorporating gender-based differences and analyzing lifting phases. Methods: 18 healthy adults (9 males and 9 females; age: 24.44 ± 4.96 years, body mass: 66.00 ± 12.10 kg, height: 170.11 ± 9.20 cm, lean body mass: 48.46 ± 7.66 kg) lifted an object 30% of their lean body mass using squat and stoop postures. Marker-based motion capture, force plate, and surface electromyography were synchronously used to acquire joint moments and muscle excitation. A 3-way mixed model analysis was performed to determine the effect of gender, posture, and phase on internal joint moments and muscle excitation of the lower back and extremities. Results: Significant differences were observed in the interaction of lifting posture and phase on lower extremity moments and excitation of rectus femoris and medial gastrocnemius. Individual effects of posture were significant for peak internal joint moments of the lower extremities only. Anterior lower extremity muscles showed significantly increased excitation during squat, whereas medial gastrocnemius was higher in stoop. Joint moments and muscle excitations were all higher during the lifting than the bending phase. Gender differences were found only in the peak lumbosacral sagittal plane moment and rectus femoris muscle excitation. Conclusions: The study identified significant variations in the joint moments and muscle excitation in lifting, influenced by gender, posture, and phase, highlighting its complex nature. Overall interactions were lacking, however individual effects were evident, necessitating larger future studies.