Maximal oxygen uptake is not limited by a central nervous system governor

Abstract

We tested the hypothesis that the work of the heart was not a limiting factor in the attainment of maximal oxygen uptake (V̇o2 max). We measured cardiac output (Q̇) and blood pressures (BP) during exercise at two different rates of maximal work to estimate the work of the heart through calculation of the rate-pressure product, as a part of the ongoing discussion regarding factors limiting V̇o2 max. Eight well-trained men (age 24.4 ± 2.8 yr, weight 81.3 ± 7.8 kg, and V̇o2 max59.1 ± 2.0 ml·min−1·kg−1) performed two maximal combined arm and leg exercises, differing 10% in watts, with average duration of time to exhaustion of 4 min 50 s and 3 min 40 s, respectively. There were no differences between work rates in measured V̇o2 max, maximal Q̇, and peak heart rate between work rates (0.02 l/min, 0.3 l/min, and 0.8 beats/min, respectively), but the systolic, diastolic, and calculated mean BP were significantly higher (19, 5, and 10 mmHg, respectively) in the higher than in the lower maximal work rate. The products of heart rate times systolic or mean BP and Q̇ times systolic or mean BP were significantly higher (3,715, 1,780, 569, and 1,780, respectively) during the higher than the lower work rate. Differences in these four products indicate a higher mechanical work of the heart on higher than lower maximal work rate. Therefore, this study does not support the theory, which states that the work of the heart, and consequently V̇o2 max, during maximal exercise is hindered by a command from the central nervous system aiming at protecting the heart from being ischemic.