ABSTRACT
The aphorism used by Peter Mitchell in his Nobel Prize lecture describing experimental progress on the chemiosmotic theory of bioenergetics, that ‘the obscure we see eventually, the completely apparent takes longer’ (Mitchell, 1978) will have resonance with anyone who has traced the origins and progress of studies investigating the character and control of the on-transient V̇O2 kinetics. It is clear that when O2 delivery is not rate limiting, the kinetics of muscle oxygen consumption follow a mono-exponential time course (Mahler, 1980; Whipp and Mahler, 1980). However, it is not clear to what extent these kinetics are regulated by O2 delivery or O2 utilization and this has been a key focus of research into V̇O2 kinetics in the last twenty years. If O2 delivery is a critical determinant of the V̇O2 kinetics, then interventions that increase O2 delivery should speed the V̇O2 kinetics beyond the control condition (which we operationally define as upright cycle exercise breathing room air at sea level). In contrast, experiments that return null results support the opposite position, that O2 utilization sets the kinetic time course, as demonstrated in isolated muscle preparations (Mahler, 1980).
