Exercise intensity has traditionally been described, prescribed and normalised as a fraction (%) of the maximal oxygen uptake ( V˙O (2max)). We hypothesised that the extent of inter-subject variability in the physiological responses to exercise would be greater when work rates were prescribed using % V˙O (2max) as compared to % 'delta' (Δ), a method of normalising exercise intensity in which both the gas exchange threshold (GET) and the V˙O (2max) are considered. 9 men completed a ramp incremental test on a cycle ergometer to establish the GET and V˙O (2max). Subsequently, subjects completed 6 constant-work-rate exercise bouts at intensities corresponding to: 50%, 70% and 90% V˙O (2max); and 60% GET, 40% Δ (that is, 40% of the difference between the GET and V˙O (2max)) and 80% Δ. For all bouts, exercise was continued for 20 min or until task failure if this occurred sooner. When exercise was prescribed using the % Δ concept, there were significant reductions in the inter-subject variability in pulmonary gas exchange, blood lactate accumulation, heart rate, and ratings of perceived exertion (all P < 0.05). In conclusion, the % Δ concept resulted in more consistent inter-subject physiological responses to constant-work-rate exercise and should be used in preference to % V˙O (2max) to more effectively normalise exercise intensity.

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IntroductionIt has recently been demonstrated that 3-6 days of dietary nitrate supplementation can reduce the O 2 cost of moderate-intensity cycle exercise and improve the tolerance of high-intensity exercise (Bailey et al., 2009). While the mechanistic bases of these effects are presently unclear, improved exercise efficiency would require either a reduced O 2 cost of ATP re-synthesis (an improved P/O ratio) or a reduced ATP cost of force production. The purpose of the present investigation was to elucidate the mechanism by which dietary nitrate supplementation enhances muscle efficiency.

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