Relationship between Blood Volume, Blood Lactate Quantity, and Lactate Concentrations during Exercise

We wanted to determine the influence of total blood volume (BV) and blood lactate quantity on lactate concentrations during incremental exercise. Twenty-six healthy, nonsmoking, heterogeneously trained females (27.5 ± 5.9 ys) performed an incremental cardiopulmonary exercise test on a cycle ergometer during which maximum oxygen uptake (V·O_2max), lactate concentrations ([La^-]) and hemoglobin concentrations ([Hb]) were determined. Hemoglobin mass and blood volume (BV) were determined using an optimised carbon monoxide-rebreathing method. V·O_2max and maximum power (P_max) ranged between 32 and 62 mL·min^-1·kg^-1 and 2.3 and 5.5 W·kg^-1, respectively. BV ranged between 81 and 121 mL·kg^-1 of lean body mass and decreased by 280 ± 115 mL (5.7%, p = 0.001) until P_max. At P_max, the [La^-] was significantly correlated to the systemic lactate quantity (La^-, r = 0.84, p < 0.0001) but also significantly negatively correlated to the BV (r = -0.44, p < 0.05). We calculated that the exercise-induced BV shifts significantly reduced the lactate transport capacity by 10.8% (p < 0.0001). Our results demonstrate that both the total BV and La^- have a major influence on the resulting [La^-] during dynamic exercise. Moreover, the blood La^- transport capacity might be significantly reduced by the shift in plasma volume. We conclude, that the total BV might be another relevant factor in the interpretation of [La^-] during a cardio-pulmonary exercise test.