The association of cardiorespiratory fitness to health independent of adiposity depends upon its expression

Background: The strong relation between cardiorespiratory fitness (CRF) and adiposity renders their independent associations to metabolic risk factors difficult to ascertain. Aim: To determine the associations of CRF and CRF relative to fat-free mass (CRFFFM) to total cholesterol, high-density lipoprotein, low-density lipoprotein, triglycerides, glucose, insulin and homeostasis model assessment (HOMA) and distinguish these relations from the association to adiposity. Subjects and methods: Anthropometrics, body fat percentage (% Fat) and fat-free mass (from dual energy X-ray absorptiometry) were measured in 127 (66 females) 17 and 23 year-olds. CRF from a maximal workload on a graded bicycle test and fasting blood samples were obtained. Results: CRF was significantly related to total cholesterol, triglycerides, insulin and HOMA (r = -0.24 to -0.49, p < 0.03), as were all adiposity measures (r = 0.21-0.53, p < 0.05). Correcting CRF for % Fat rendered the relation to metabolic risk factors non-significant (p = 0.09-0.21); however, CRFFFM was significantly related to the metabolic risk factors (r = -0.25 to -0.32, p < 0.02). Conclusions: CRFFFM, where adiposity has been removed, is associated with metabolic risk factors, whereas CRF, which is related to adiposity, is not after adjustment for fatness. Previously, independent effects of CRF on health may have been underestimated by using an expression of CRF strongly related to the adiposity measures.