We aimed to compare the anaerobic alactic (AnAL) energy expenditure from a 50-m front crawl swimming between two methodologies in highly trained short-distance swimmers: (i) based on the maximal phosphocreatine (PCr) splitting in contracting muscles (AnALPCRSPLITTING) and (ii) based on the oxygen uptake ( VO2) off-kinetics, where AnAL is estimated from the area under the curve of the fast component (amplitude in liters×time constant in minutes) of the 10-minute of excess postexercise oxygen consumption (AnALVO2KINETICS). Thirty-nine 50-m front-crawl all-out (time trial) swimming performances and respective off-transient kinetics pulmonary VO2 samples (23 men: 17.0±2.6 y and; 16 women: 17.0±2.1 y) were analyzed. We observed no differences (n2p=0.044; p=0.068) between AnALPCRSPLITTING (41.7±6.1 kJ) and AnALVO2KINETICS (37.6±12.7 kJ). Bland-Altman plots indicated high bias (3.79-4.42 kJ) and precision (agreement) (limits:-21.31 to 30.14 kJ) between methods, with repeatability ranging from "poor" to "moderate" (intraclass correlation coefficients: 0.34-0.53; p=0.018-0.157), indicating proportional error that varies with the magnitude of the measurements. Although both methods showed overall agreement, their conceptual and methodological differences introduce proportional error. Thus, they should not be used interchangeably, but rather considered complementary, when feasible, to provide a more comprehensive understanding of AnAL energy expenditure in short-duration maximal efforts such as 50-m swimming.
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