BURNLEY, MARK1; DOUST, JONATHAN H.2; VANHATALO, ANNI1
The present study has shown that a 3-min all-out cycle ergometer test against a fixed resistance results in a reproducible power output profile and in the attainment of V·O2peak, which is consistent with our first and second hypotheses (Figs. 1 and 3B). The end-test power output was above that associated with the GET but below the power output achieved at the end of the ramp test (Figs. 2 and 3). Our third hypothesis was that this end-test power output would represent the boundary between the heavy- and severe-exercise intensity domains. Therefore, we predicted that constant-work rate exercise performed below this power output would result in steady-state blood [lactate] and V·O2 responses, whereas exercise above the end-test power output would result in a continued rise in these variables until fatigue ensued. The present study provides some support for this hypothesis: 9 of the 11 subjects were able to complete 30 min of exercise at 15 W below the end-test power, and seven of these met the criteria for a steady-state blood [lactate] profile (Fig. 4). In contrast, none of the subjects completed 30 min of exercise 15 W above the end-test power output, and in all cases blood [lactate] and V·O2 continued to rise until exhaustion, at which point V·O2 did not differ significantly from V·O2peak. These data suggest that it is possible to establish V·O2peak during a 3-min all-out exercise test and that this test also represents a promising method of identifying the maximal steady-state power output in a single test.
All-out exercise tests are typically used for measuring maximum dynamic power output. Consequently, test duration is usually limited to less than 90 s (30). Some previous reports have suggested that all-out tests can be used to establish V·O2peak in adults (12) and adolescents (29), whereas others have not (13,30). The present results show that V·O2peak can be achieved during all-out exercise even when the power output falls considerably below levels associated with the achievement of V·O2peak during ramp exercise (Table 1, Figs. 1 and 3). It is well established that the work rate need not be maximal for subjects to achieve V·O2peak; submaximal constant-work rate exercise performed in the severe-intensity domain results in a V·O2 slow component that drives V·O2 to V·O2peak before fatigue ensues (7,14,23). It is now also clear that all-out exercise lasting 1.5-3 min also yields V·O2peak, with little evidence of V·O2 declining towards the end of the test in adolescents or adults ((29), present study). These data add to the growing body of evidence that V·O2peak can be established using a variety of work rate-forcing functions. Ramp/incremental tests, all-out tests lasting 1.5-3 min, and submaximal constant-work rate tests in the severe-intensity domain performed to volitional exhaustion all result in the same end-point V·O2 (i.e., V·O2peak) (7,29).
A common feature of previous work investigating prolonged all-out exercise is that the power output falls below that associated with the attainment of V·O2peak in a ramp or incremental exercise test (6,8,12,29,30). It was our original contention that if the fall in power was continued until a leveling out could be identified, the end-test power would equal the power output demarcating the heavy- and severe-intensity domains. This contention stems from the fact that the power-duration relationship is hyperbolic (19-21), with the critical power representing the maximal steady-state power output (20) and W′ representing a fixed amount of work that can be performed above critical power (9). We reasoned that if the performance of all-out exercise were continued for long enough to reduce W′ to zero, then the end-test power output would necessarily equal the maximal steady state. We did not, however, establish the parameters of the power-duration relationship in the present study. The definition of critical power requires mathematical extrapolation of the results of a series of exhaustive exercise tests to the asymptote on the power axis (10), which may (20,21) or may not (4,22) yield a maximal steady-state power output. In establishing the critical power, therefore, the physiological response profile above and below the hypothesized heavy-severe boundary (the end-test power) would have remained uncertain. Instead, we chose to directly address the physiological responses to exercise above and below the end-test power output, using a previously established criterion for the achievement of a blood [lactate] steady state (an increase in blood [lactate] of < 1 mM between 10 and 30 min of exercise) (4,15,17). Thus, if the end-test power successfully defined the boundary between heavy- and severe-intensity exercise, a steady-state blood [lactate] response below, but not above, this power would be expected.
Individual responses to 3 min of all-out test
Figure 1: Correlation and Bland-Altman analyses for the difference between ramp-determined V·O2 and V·O2peak measured during all-out exercise (panels A and B) and the end-test power output during the all-out test (panels C and D). In panels A and C, the solid line is the best-fit linear regression, and the dashed line is the line of identity. In panels B and D (Bland-Altman plots), the solid horizontal line represents the mean difference between the two measures, and the dashed lines represent the 95% limits of agreement between the measures.
Figure 2: Group mean power output during the 3-min all-out test (panel A).Dashed lines represent the standard deviation. Panel B shows the group mean power output averaged every 30 s. Asterisks indicate a significant difference in power output from the previous time period. Note that power output reaches a plateau in approximately 120 s in panel A and that end-test power output is not significantly different from the preceding power output in panel B, in contrast to all other time points.