Relationship between muscle blood flow and oxygen uptake during exercise in endurance-trained and untrained men

A recent study showed good correlation between regional blood flow (BF) and oxygen uptake ((V) over dot O-2) 30 min after exhaustive exercise. The question that remains open is whether there is similar good correlation between BF and V. O2 also during exercise. We reanalyzed our previous data from a study in which BF and (V) over dot O-2 was measured in different quadriceps femoris muscles in seven healthy endurance-trained and seven healthy untrained men at rest and during low-intensity intermittent static knee-extension exercise (Kalliokoski KK, Oikonen V, Takala TO, Sipila H, Knuuti J, and Nuutila P. Am J Physiol Endocrinol Metab 280: E1015 - E1021, 2001). When the mean values of each muscle were considered, there was good correlation between BF and (V) over dot O-2 during exercise in both groups (r(2) = 0.82 in untrained and 0.97 in trained). However, when calculated individually, the correlations were poorer, and the mean correlation coefficient (r(2)) was significantly higher in the trained men (0.71 +/- 0.07 vs. 0.40 +/- 0.11, P = 0.03). These results suggest that there is large individual variation in matching BF to (V) over dot O-2 in human skeletal muscles during exercise, ranging from very poor to excellent. Furthermore, this matching seems to be better in the endurance-trained than in untrained men.