2022 Volume 42 Pages 113-121
This study aimed to evaluate mechanical stress placed on each lumbar intervertebral disk during high-load back squat exercise using magnetic resonance （MR） imaging and assess the relationship between degree of mechanical stress and individual intrinsic physical factors such as lumbar lordosis angle, trunk muscle size, and lower extremity flexibility. Thirteen participants （11 males and two females） performed parallel back squat exercises （80% of one repetition maximum, eight repetitions, five sets） using a Smith machine. Sagittal MR diffusion-weighted images of the lumbar spine were obtained using a 1.5-Tesla MR system with a spine coil before and immediately after the exercise to calculate apparent diffusion coefficient （ADC; an index of water movement within tissues） values of all lumbar intervertebral disks. Additionally, lumbar lordosis angle and muscle cross-sectional area of each trunk muscle were evaluated using MR imaging before the exercise. Passive range of motions of hip flexion and ankle dorsiflexion were assessed using digital photos and an image processing software （Image J） before the exercise. ADC values of the L4/5 and L5/S1 intervertebral discs significantly decreased after squat exercise （P < 0.01） . However, the changes were not significantly correlated with lumbar lordosis angle, cross-sectional areas of the trunk muscles, and passive range of motion of hip flexion and ankle dorsiflexion. The study findings suggest that lower lumbar intervertebral disks are subject to great mechanical stress during high-load parallel back squat exercises and that changes are not related to individual physical intrinsic factors such as lumbar lordosis angle, trunk muscle size, and lower extremity flexibility
