Relationship of lumbar-hip kinematics during trunk flexion and sex, body mass index, and self-reported energy expenditure: a cross-sectional analysis

Purpose Physical activity (PA) is a well-known, simple and effective preventive and therapeutic intervention for low back pain (LBP). In spite of the growing interest in active lifestyles and its benefits, more needs to be known about the relationship between energy expenditure, body mass and lumbar-pelvic kinematics during the forward bending movement in a group of young asymptomatic people who met PA guidelines. Young people can be identified as a future risk group of civilisation diseases and lumbar-hip kinematics can be considered as a predictor of LBP occurrence. The aim of this study was to identify the association of sex, self-reported energy expenditure, body mass index, and lumbar-hip kinematics in young people. Methods Sixty-four students at pre-employment stage participated in the study. They declared moderate-to-high PA and activity-induced energy expenditure (AEE) was self-reported. Kinematic data of the lumbar spine, pelvis, and hip were collected during forward bending using a 3D motion capture system. Results Sex was found to be associated with pelvis (β=-0.38 p=0.002) and lumbar mobility (β=0.49, p<0.001) during forward bending and BMI was related only to lumbar mobility (β=-0.41, p=0.001). Recreation AEE significantly predicted hip flexion mobility (β =0.38, p=0.002). Conclusions This study showed that among a sample of physically active young people, BMI, self-reported AEE, and sex can partially predict lumbar-hip kinematics during trunk flexion. Recreational PA can be regarded as improving hip mobility and thus making forward bending more effective and less prone to injury.