Lumbar curvature in standing and sitting in two types of chairs: relationship of hamstring and hip flexor muscle length.

A purpose of this study was to determine the difference in the lumbar curves of subjects while they stood compared with while they sat in two chairs with different seat angles--the Balans Multi-Chair (BMC) and a standard conventional chair (SCC). An additional purpose was to determine the relationship between lumbar curvature and 1) anthropometric factors and hamstring and hip flexor muscle length during standing and during sitting in the two chairs and 2) amount of time spent sitting. Sixty-one men between 20 and 30 years of age served as subjects. Lumbar curve measurements were taken with a flexible ruler with the subjects first standing and then sitting in the two chairs. Hamstring and hip flexor muscle lengths were indicated by range-of-motion measurements taken with a gravity goniometer. Age, number of hours spent sitting per day, upper body length, and right leg length also were recorded. Subjects had significantly more lumbar extension when they sat in the BMC than when they sat in the SCC. Hip flexor length was the only factor that appeared to relate significantly to the difference between the standing lumbar curve and the lumbar curves in the BMC and the SCC.