Influence of the hamstring muscles on lumbar spine curvature in sitting.

The hamstring muscles can restrict hip flexion, especially when the knees are extended. It was hypothesized that individuals with short or tight hamstrings would have abnormal tilting of the pelvis in some seated postures, with greater flattening or reversal of the lumbar lordosis. Healthy adults were studied. A toe-touch test was used to measure range of hip flexion. Lumbar spine curvature was measured in standing, in sitting with the knees flexed, and in sitting with knees partially extended. Large individual variations in range of hip flexion were found. Persons with a small range had the most pronounced change in spine curvature in the second seated posture. It is concluded that attention should be given to this effect of the hamstrings on the lumbar spine when workplaces are designed.