Objectives Cardiorespiratory fitness (CRF) has been inversely associated with risk of cardiometabolic diseases. However, there are no studies comparing the independent associations of CRF scaled by body size and composition using different approaches with cardiometabolic risk factors between children and adults. We therefore investigated these associations in children and adults using same measures for CRF and cardiometabolic risk factors.

Design Cross-sectional.

Methods A total of 352 children (47.2 % girls) and 572 men were included in the study. Peak oxygen uptake (V̇O2peak) was measured during a maximal exercise test on a cycle ergometer and was scaled by total body mass (BM−1), total fat free mass (FFM−1), and allometrically modelled BM, FFM, and stature. Insulin, glucose, triglycerides, HDL cholesterol, and LDL cholesterol were assessed from fasting blood samples and systolic and diastolic blood pressure were measured. HOMA-IR and continuous metabolic risk score were computed.

Results V̇O2peak scaled by BM−1 was inversely associated with insulin, HOMA-IR, triglycerides, diastolic blood pressure, the cardiometabolic risk score and the number of cardiometabolic risk factors in children and adults. However, these associations attenuated remarkably when V̇O2peak was scaled by total FFM or allometrically modelled BM, FFM, or stature. V̇O2peak was consistently and positively associated with HDL cholesterol in children and adults irrespective of the scaling approach.

Conclusions The inverse associations of CRF with cardiometabolic risk factors among children and adults attenuated remarkably when body size and composition were appropriately controlled for. However, the positive association between CRF and HDL cholesterol was consistent irrespective of the scaling approach.