1. In 12 high-performance athletes at rest, during work at the bicycle ergometer, and during recovery, we measured oxygen pressure, carbon dioxide pressure, pH, standard bicarbonate, and base excess of the blood flowing primarily from the working muscles and of the arterial blood. The values arrived at were compared with comparable data derived for untrained persons. 2. Neither in the trained nor in the untrained persons was the critical venous oxygen pressure reached during maximum exertion. This is evident not from the data concerning femoral venous oxygen pressure during maximum exertion, but rather from the behavior of the lactate/pyruvate ratio. 3. Continued high performance of a trained athlete at sea level is probably not limited by the oxygen supply to the muscle tissue or by the acidation of the blood or tissue. 4. The decrease in the venous oxygen pressure during exertion does not cause the increased lactate output, which is observed earlier and more intensively in untrained than in trained persons. Rather, this seems to be a result of limited oxydative cell performance. 5. The following results, differing for athletes and non-athletes, indicate that during exertion athletes are characterized by a higher blood circulation level than untrained persons (this is probably an important factor in continued performance). During light activity, the athletes' Po20076-0304 decreases only minimally. A stress level of 200 watts, representing maximal work for the non-athlete, represents only submaximum work for the athlete. Here the femoral venous O2-pressure amounts to about 21 mm Hg in both groups. The trained athlete is able to increase his performance further to 300 watts, without a further significant decrease in Po20076-0304. This cannot be wholly explained by a right-hand shift of the O2-dissociation curve under the influence of pH and temperature change. 6. Only in the arterial blood pH under stress is determined chiefly by the lactate output. pH20076-0304 is also significantly dependent on the CO2-pressure. Neither in the arterial nor in the femoral venous blood do athletes show lower pH-values under maximum stress than untrained persons. Therefore neither increased acidation of the tissue during maximum exertion, nor an increased acid tolerance of the tissue due to training, is probable. © 1968 Springer-Verlag.
