Aim: Physical activity (PA) and cardiorespiratory fitness (CRF) are indicators of cardiovascular disease risk and all-cause mortality. Many health advocates use PA and CRF interchangeably. However, quantification of the relationship between objectively measured PA and CRF is rarely found.
Methods: The association between objectively measured PA volume (PAv), intensity (PAi), and CRF indexed by V.O(2max) was assessed in a cross-sectional study; 275 women (40.1+/-3.0 years) wore accelerometers at the hip for seven days. They performed a graded maximal treadmill test to measure CRF and had their percent body fat (%BF) assessed.
Results: PAv (F=12.33, P<0.0001) and PAi (F=48.5, P<0.0001) were both significant predictors of CRF, together accounting for 26.9% of the variance (P<0.0001). However, with PAi controlled, PAv was not related to CRF. Yet, with PAv controlled, PAi remained a strong predictor. %BF explained 47% (P<0.0001) of the variance in CRF.
Conclusions: CRF is more a function of PAi than PAv in middle-aged women. More than 70% of the variance in CRF can be explained by factors other than PA, particularly %BF, suggesting that CRF may not be an appropriate surrogate for PA.