ABSTRACT
The tools necessary for the accurate characterization of the transient oxygen uptake (V̇O2) response, namely a range of ergometers, gas analysers, flow meters and the mathematical techniques for data analysis, have been well developed throughout the last century. In recent years, experimental focus has shifted increasingly towards using these tools to characterize the V̇O2 time course at exercise onset and to address problems related to metabolic control Of recent interest is that the V̇O2 response to exercise can be altered considerably when different ergometers are used to impose the desired work rate (Koga et al., 1996; Billat et al., 1998a; Jones and McConnell, 1999; Carter et al., 2000b; Koga et al., 2001; Koppo et al., 2002; Pringle et al., 2002). These findings imply that the V̇O2 response kinetics may be strongly influenced not only by metabolic factors and perhaps O2 delivery to the working muscle (Tschakovsky and Hughson, 1999), but also by the muscle contraction regimen and the ensuing muscle fibre recruitment profile itself. This chapter will consider that latter factor in detail, where possible providing the likely physiological mechanisms that may explain the observed differences between exercise modalities. The focus is principally upon the V̇O2 response to exercise (i.e. the ‘on’-kinetics) rather than to recovery (i.e. the ‘off’-kinetics), largely because few studies have specifically addressed the relationship between the on- and off-transient kinetics across exercise modalities. However, it is evident that that there may be differences in the nature of the V̇O2 off-response across different exercise modalities relative to the on-response and across exercise intensity domains (Carter et al., 2000b; Perrey et al., 2002; Rossiter et al., 2002), at least when compared to the characteristics of the on- and off-transient responses described for cycle exercise (Paterson and Whipp, 1991; Özyener et al., 2001).
