FACTORS INFLUENCING WORK CAPACITY IN ADOLESCENT IDIOPATHIC THORACIC SCOLIOSIS

The factors contributing to reduced work capacity (disability) in adol escent idiopathic thoracic scoliosis are poorly understood. We perform ed a cross-sectional study using multivariate analysis to identify the individual and additive influence of spinal deformity, pulmonary impa irment, and muscular function on work capacity in 79 subjects with idi opathic scoliosis (angle of scoliosis 45 +/- 18.5-degrees, SD). Work c apacity was measured using an incremental cycle test, and the cardiore spiratory response to exercise was compared with that of normal subjec ts. Work capacity was reduced (% Wcap, 86%; 95% Cl 81.9 to 89.7), indi cating significant disability. The % Wcap was unrelated to the nature and extent of spinal deformity (p > 0.05). Leg muscularity and pulmona ry impairment had an additive influence on work capacity, the relation ship with muscularity being the stronger of the two. Independently of muscularity and pulmonary impairment, a high heart rate response at su bmaximal work rates was also associated with a reduced work capacity. Ventilation was normal for metabolic demands. During exercise, the tid al volumes of scoliotic subjects were reduced in proportion to the vit al capacity. We conclude that disability occurs with mild to moderate idiopathic scoliosis and appears to be related to a combination of red uced ventilatory capacity, reduced muscularity, and cardiovascular dec onditioning. These findings suggest that physical activity should be e ncouraged in subjects with idiopathic scoliosis to maintain peripheral muscle and cardiovascular conditioning, thereby minimizing disability .