Lumbar spine loading during half-squat exercises.

Evaluation of the compressive load acting on the lumbar spine (L3-L4) during half-squat exercises executed with a barbell resting on the subject's shoulders was undertaken. The kinematics of the upper body segments of two male and two female subjects as well as the barbell were described using data obtained by means of an optoelectronic system (CoSTEL). L3-L4 compressive load was calculated using a model of the anatomy of the trunk musculoskeletal system. Filtered surface electromyographic trunk flexor recordings from the obliquus externus and rectus abdominis and trunk extensor erectores spinae muscles as well as measurement of the ground reaction forces were also carried out for predicted result validation. During half-squat exercises with barbell loads in the range 0.8 to 1.6 times body weight the compressive loads on the L3-L4 segment vary between 6 and 10 times body weight. Erectores spinae contraction force was predicted to be between 30 and 50% of the relevant maximal isometric force. The magnitude of trunk flexion was found to be the variable which influenced most spinal compression load.