Letter-to-the editor W'
reconstitution is exponential and depends on recovery intensity and duration
Kevin Caen1, Jan G. Bourgois1, Jan Boone1
1Department of Movement and Sport Sciences, Ghent University, Ghent, Belgium
With great interest, we have read the study of Sreedhara et al. (1), in which it is reported that recovery power output (PREC) has a stronger impact than recovery duration (tREC) on the curvature constant (W') reconstitution of critical power (CP). More specifically, they reported that W' recovery was higher at low intensity (PREC-L = 75-90 W) vs. moderate intensity (PREC-M
= 90% of the power output at the gas exchange threshold, PGET) vs. high intensity (PREC-H = PGET + 50% of the difference between CP and PGET)) exercise, whereas W' recovery did not improve (over all recovery intensities) from 2 to 15 min. These results are in contrast to other studies demonstrating a progressive and curvilinear W' reconstitution with prolonged duration (2,3) and decreasing recovery intensity (3,4). In our opinion, these contrasting findings are predominantly related to methodological issues. First, at PREC-L, W' reconstitution after 2 min of recovery is already 33.7 ± 10.1%. Given that theoretically, only 50% of W' has been depleted in the experimental trial (i.e., 2 min cycling at an intensity that would result in exhaustion in 4 min, CP4), W' has been recharged to 83.7% and thus the margin for tREC to exert its effect is small. Second, and perhaps most important, Sreedhara et al. (1) have determined PREC-M and PREC-H from a ramp incremental test without taking into account that power output corresponding to any given oxygen uptake ( V´ O2) during ramp exercise (e.g., at GET) exceeds the constant power output that will elicit that specific V´ O2 (5). As a consequence, the power output obtained and used in PREC-M will have induced a steady-state V´ O2 that exceeds the true GET and thus, this recovery condition will have been situated in
the (middle or upper part of the) heavy intensity domain. This can also be deduced from the high PGET relative to peak power output (61.1 ± 8.2%) and relative to CP (81.3 ± 8.3%).
Additionally, in this context, we believe that PREC-H exceeded the highest metabolic steady- state power output in one or more subjects. In subjects 1, 4 and 5, the difference between the CP and PGET is 18-27 W, indicating that the PREC-H is only 9-14 W below CP determined from the 3-min all-out test. It is important to remember that the good reliability of the 3-min all-out test, as demonstrated in this study, does not necessarily equate to the validity of the obtained CP and W' estimates. On average, CP determined from constant load trials to exhaustion exceeds maximal lactate steady-state by 11% (6), and furthermore, it has been shown that CP derived from a 3 min all-out test exceeds CP determined in the traditional way (7,8).
Therefore, it is likely that one or more subjects were still cycling above the power output that would allow reconstitution of W' (i.e., maximal metabolic steady-state). This would explain the small and even negative (in the 15-min condition) W' reconstitution and the presence of a large standard deviation at PREC-H. In summary, despite the interesting results with regard to W' reconstitution following partial depletion, we believe that, due to the methodological issues, the study of Sreedhara et al. (1) does not challenge the concept of a curvilinear W' reconstitution that depends both on recovery intensity and duration.
1. Sreedhara VSM, Ashtiani F, Mocko GM, Vahidi A, Hutchison RE. Modeling the recovery of W’ in the moderate to heavy intensity domain. Med Sci Sports Exerc. 2020 (published ahead of print).
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