The final frontier: oxygen flux into muscle at exercise onset.

In humans at exercise onset, intramuscular phosphocreatine decreases immediately, whereas muscle oxygen (O2) uptake seems to rise after a delay of up to 15 s which is inconsistent with models of metabolic control. Novel microcirculatory investigations reveal that elevated capillary-to-myocyte O2 flux in rat muscle is, in fact, initiated simultaneously with contractions.