Blood flow and muscle oxygen uptake at the onset and end of moderate and heavy dynamic forearm exercise

We hypothesized that forearm blood flow (FBF) during moderate intensity dynamic exercise would meet the demands of the exercise and that postexercise FBF would quickly recover. In contrast, during heavy exercise, FBF would be inadequate causing a marked postexercise hyperemia and sustained increase in muscle oxygen uptake ((V) over dot O-2musc). Six subjects did forearm exercise (1-s contraction/relaxation, 1-s pause) for 5 min at 25 and 75% of peak workload. FBF was determined by Doppler ultrasound, and O-2 extraction was estimated from venous blood samples. In moderate exercise, FBF and (V) over dot O-2musc increased within 2 min to steady state. Rapid recovery to baseline suggested adequate O-2 supply during moderate exercise. In contrast, FBF was not adequate during heavy dynamic exercise. Immediately postexercise, there was an similar to 50% increase in FBF. Furthermore, we observed for the first time in the recovery period an increase in (V) over dot O-2musc above end-exercise values. During moderate exercise, O-2 supply met requirements, but with heavy forearm exercise, inadequate O-2 supply during exercise caused accumulation of a large O-2 deficit that was repaid during recovery.