ABSTRACT
One of the major features of an effectively functioning physiological system is its ability to respond to a particular stressor with rapid response characteristics. For example, during muscular exercise the greater the aerobic contribution to the energy transformations that fuel the muscular contraction the less is the reliance on anaerobic mechanisms – which are major contributors to the fatigue process (e.g. Hepple, 2002; Westerblad et al., 2002 for review). A rapid dynamic response profile of O2 uptake is, consequently, a characteristic feature of subjects manifesting high exercise tolerance (e.g. Hagberg et al., 1980; Powers et al., 1985; Whipp et al., 2001). In order to understand the mechanisms controlling O2 uptake at the lung (V̇O2), the O2 consumption in the skeletal muscle (mV̇O2), and the factors that can dissociate them, it is naturally important to establish a precise characterization of the time course in order to draw justifiable control inferences. mV̇O2, for example, is known to be controlled by enzymatic processes linked to high-energy phosphate turnover in the muscle: hence the ‘expected’ response profile is exponential (e.g. Chance et al., 1955; Owen and Wilson, 1974; Holian et al., 1977; Bessman and Geiger, 1981; Mahler, 1985; Saks et al., 2001; and see Wilson, 1994 for review). And so the attention given to exponential analysis is not that it is simply a convenient fitting strategy – there are other models that would give a more or less adequate fit to the data – it is that the exponential provides the potential for establishing justifiable physiological equivalents of the response parameters. An understanding of the basic features of the exponential is therefore essential to making physiological inferences from exercise transients.
