Body mass as a factor in stature change.

BACKGROUND Back pain is a common condition which has been described as a serious public health problem. Spinal shrinkage has been used as an index of spinal loading in a range of tasks. Epidemiological evidence shows that body mass index (BMI: 30 kg/m(2)) is related to the development of low back pain however, no studies have described the stature change patterns of obese individuals. This study aimed to compare changes in stature after an exercise task in obese and non-obese individuals. METHODS Twenty volunteers were divided into two equal groups; obese: BMI>30 kg/m(2), non-obese: BMI<25 kg/m(2). Stature was measured at 3 min intervals during a 30 min walking task and a 30 min standing recovery period. Tests were performed on two occasions, once with participants loaded during the walking task (10% body mass) and once unloaded. The influence of obesity and load condition on the magnitude and rate of stature change were compared by a two-way ANOVA: FINDINGS In both groups the stature loss was greater in the loaded than unloaded condition (mean (SD)) (6.52 (1.45)mm and 3.55 (0.93)mm non-obese; 8.49 (1.75)mm and 7.02 (1.32)mm obese: P=0.016). The obese presented a greater reduction in stature in both task conditions. The obese group were unable to recover stature regardless of the task condition during the recovery period (loaded: 0.06 (0.3)mm; unloaded: 0.32 (0.6)mm; P=0.013). INTERPRETATION It was concluded that the acute response of the spine to loading may represent a risk factor for low back pain in the obese, in addition to the chronic adaptations previously reported. A greater period of recovery may be necessary for obese individuals to re-establish intervertebral disc height. These findings may help to explain the high incidence of back disorders in obese individuals.