Acute effects of varying squat depths on lumbar intervertebral disks during high-load barbell back squat exercise

We aimed to evaluate the acute physiological effects of high-load barbell back squat exercise on each lumbar intervertebral disk with varying squat depths. Thirteen subjects (age, 23.3 ± 3.5 years) performed parallel and half-squat exercises (80% of one repetition maximum, eight repetitions, five sets) using a Smith machine. Sagittal magnetic resonance diffusion-weighted and spin-echo images of lumbar intervertebral disks were obtained by using a 1.5-Tesla MR system before and after each squat exercise; apparent diffusion coefficient (ADC; an index of water movement) and T₂ relaxation time (an index of water content level) of the nucleus pulposus were calculated at all lumbar intervertebral disks. Additionally, we measured the angles of lumbar lordosis and anterior pelvic tilt at the bottom position of each squat using a three-dimensional motion-capture system. The nucleus pulposus of L4/5 (-5.0%, P < .01) and L5/S1 (-6.6%, P < .01) intervertebral disks showed decreased ADC values after parallel squat exercise. Moreover, post-exercise ADC value in parallel squat exercise was lower than that in half-squat exercise at L5/S1 intervertebral disk (P < .05). In contrast, the nucleus pulposus of all lumbar intervertebral disks had no significant T₂ change before and after both squat exercises. The angles of lumbar lordosis (P < .01) and anterior pelvic tilt (P < .01) were smaller in parallel squat than in half-squat. Lower lumbar intervertebral disks are subject to greater mechanical stress during high-load parallel back squat exercise, which may result from smaller lumbar lordosis and anterior pelvic tilt angles at the bottom position during parallel squat.