Physical Activity, but Not Aerobic Capacity, Correlates With Back Strength in Healthy Premenopausal Women From 29 to 40 Years of Age

Abstract

The correlation of muscle strength at various sites of the axial and appendicular skeleton with physical activity and aerobic capacity was assessed in women 29 to 40 years old. Muscle strength of the spine and upper extremities was determined with strain gauges in 96 healthy white women, and power grip was used as an indicator of upper extremity strength. The physical activity score, which reflected the level of daily weight-bearing activity and was based on a standardized scale, ranged from 3 to 15. Maximal oxygen uptake (aerobic capacity) was measured in 69 of the 96 subjects. The mean values for maximal oxygen uptake were 1.9 liters/min and 27.9 ml/kg per minute when normalized for weight. In general, muscle strength was significantly correlated between axial and appendicular sites; thus, the axial musculature usually represents overall muscle strength. Maximal oxygen uptake in milliliters per kilogram per minute was not correlated with back extensor strength or upper extremity strength. Physical activity score was significantly correlated with back extensor strength but not with maximal oxygen uptake (aerobic capacity) either in liters per minute or in milliliters per kilogram per minute. Thus, maximal oxygen uptake is an invalid marker for level of daily weight-bearing physical activity.