Abstract
PURPOSE: Oxygen delivery to the skeletal muscle through the cardiovascular system is commonly regarded to be the most important factor limiting maximal oxygen uptake (VO2max) during exercise in humans. Total haemoglobin mass (mHb), blood volume (B V) and cardiac output (determined by heart volume (HV) and stroke volume) are major contributors characterizing the performance of the cardiovascular system's oxygen transport capacity. No data is available regarding the interaction of these variables with respect to their influence on VO2max. The aim of the present study was therefore to compare the influence of mHb, BV and HV on VO2max and to detect interactions between these factors. METHODS: In 89 of healthy male athletes from various sports, mHb was determined using the optimized CO-rebreathing method, HV was measured by echocardiography, VO2max was established from exercise testing data (ergometry until volitional exhaustion). The results were normalized for body mass (rHb, rBV, rHV, rVO2max). All data was log-transformed before processing and analysed using methods of linear regression. RESULTS: In stepwise regression, log(rVO2max)= A+ B1 * log(rHV) + B2 * log(rHb) was identified as best fit (R2= 0.67, RMSE=0.12; A=1.3±0.22; B1=0.65±0.09, B2=0.46±0.10, (for p<0.0001)). According to this model, 66% (R2adj) of rVO2max can be explained by rHV and rHb. The inclusion of rBV did not improve the model. As a measure for interaction between rHV and rHb, partial correlation with r (log rHV, log rHB | log rVO2max)=0.16; (p=0.15) revealed statistical independence of rHV and rHb in the determination of VO2max. CONCLUSIONS: R2 of our model is in line with previously published data on VO2max modelling. The new finding of this investigation is the fact that the model is based on directly measured mHb data and unveils rHV and rHb as independent determinants of rVO2max. This strengthens the theory that factors limiting VO2max are “dispositional attributes”, yielding variability in their response within a certain frame depending on the state of the system, rather than “manifest attributes”, predefined in the magnitude of their functional capacity. rHb and rHV are independent determinants of VO2max. Our findings might add to the discussion on VO2 max limitation.
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