Muscle metabolic profile and oxygen transport capacity as determinants of aerobic and anaerobic thresholds

Aerobic and anaerobic thresholds determined by different methods in repeated exercise tests were correlated with cardiorespiratory variables and variables of muscle metabolic profile in 33 men aged 20–50 years. Aerobic threshold was determined from blood lactate, ventilation, and respiratory gas exchange by two methods (AerT₁ and AerT₂) and anaerobic threshold from venous lactate (AnT_La), from ventilation and gas exchange (AnT_r) and by using the criterion of 4 mmol·l⁻¹ of venous lactate (AnT_4mmol). In addition to ordinary correlative analyses, applications of LISREL models were used. The 8 explanatory variables chosen for the regression analyses were height, relative heart volume, relative diffusing capacity of the lung, muscle fiber composition, citrate synthase (CS) and succinate dehydrogenase activities, the lactate dehydrogenase — CS ratio, and age. They explained 58% of the variation in AerT₁, 73.5% that of AerT₂, 71% that of AnT_r, 74.5% that of AnT_La, and 67.5% that of AnT_4mmol. AerT and AnT alone explained 77% of the variation in each other. Both AerT and AnT were determined mainly by a muscle metabolic profile, with the CS activity of vastus lateralis as the strongest determinant. The factor ‘submaximal endurance’ which was measured with AerT and AnT seemed to be slightly more closely connected to ‘muscle metabolic profile’ than was ‘maximal aerobic power’ (\(\left( { = \dot V_{O_{2max} } } \right)\)), but both also correlated strongly with each other (r = 0.92).