ABSTRACT
Daily life is full of challenges in which the energy demands of the working muscles might quickly go from rest to substantial loads. It is critical, therefore, to understand the factors that regulate how quickly aerobic metabolic pathways adapt to these challenges. This knowledge will then provide a key to exploring the consequences of impaired function due to disease or environment. However, there are many controversies over the specific factors that regulate the rate of increase in oxygen uptake (V̇O2) at the onset of different intensities of exercise. Recent reviews (Tschakovsky and Hughson, 1999a; Grassi, 2001; Hughson et al., 2001) have highlighted some of the factors to consider in exploring debates that have persisted for over twenty years (Whipp and Mahler, 1980; Hughson and Morrissey, 1983). It is also critical to explore reviews that have focused on regulation of blood flow especially at the onset of exercise (Laughlin et al., 1996; Saltin et al., 1998; Delp, 1999; Hughson and Tschakovsky, 1999; Shoemaker and Hughson, 1999) and muscle metabolism (Di Prampero, 1981; Wilson and Rumsey, 1988; Tschakovsky and Hughson, 1999a; Greenhaff et al., 2002).
