In swimming, the velocity corresponding to the maximal lactate steady state (MLSSv), is the highest intensity that can be maintained over time without continuous blood lactate accumulation, defines the transition between heavy and severe domains of intensity, characterized by differences in VO2 kinetics (Reis et al., 2011) and stroke parameters (Dekerle et al., 2005). The purpose of this study was to analyze the physiological and mechanical responses at and above MLSSv in swimming. Methods: Twelve competitive male swimmers completed an incremental test composed by 5x250 and 1x200 m front crawl for VO2max determination. For MLSSv estimation, subjects performed, in random order and different days, 30-min at constant velocity at 87.5, 90 and 92.5% of vVO2max. In a complementary day, two 6-min bouts were performed separated by one hour of passive rest between each repetition at 102.5% of MLSSv. Respiratory gases exchange was analized using a K4b2 unit with a "aquatrainer" swimming snorkel (Cosmed®). The parameters of the VO2 kinetics were modelled with two exponential functions. Best 400 and 800 m performances in a swimming competitive event were recorded (respectively, T400 and T800). Results: MLSSv was achieved by all athletes at 90% of vVO2max (1.30 ± 0.04 m/s). The athletes completed the two 6-min bouts at a mean swimming velocity of 1.34 ± 0.04 m/s with seven swimmers exhibiting relevant slow component (mean value 41.4 ± 21.4 ml/min), 1.1% of VO2max (3767.67 ± 483,86 ml/min). Maximal lactate steady state (4.6 ± 1.2 mmol/L) was significantly lower (p < 0.01) than at 102.5% MLSSv (7.4 ± 1.4 mmol/L), the same was also verified concerning the stroke rate (33.3 ± 3.8 vs 37.8 ± 4.1 cycles.min-1) and rate of perceived exertion (5.8 ± 0.6 vs 7.6 ± 1.0 in a 0-10 scale). Contrarily, stroke length significantly decreased above MLSSv (2.41 ± 0.27 vs 2.17 ± 0.20 m/cycle). MLSSv was inversely correlated to VO2 primary phase time constant (tp) (r= -0.59; p < 0.04). This last parameter was also correlated with T800 (r = 0.58; p < 0.05). Discussion: Our results corroborate the assumption that MLSSv represents an exercise intensity above which swimmers have to adopt different strategies to deal with fatigue, decreasing stroke length and relying on higher stroke rate in order to maintain a constant velocity for a longer period of time. VO2 kinetics time constant is related to exercise tolerance and performance, in line with previous results (Reis et al., 2011).
© Copyright 2012 17th Annual Congress of the European College of Sport Science (ECSS), Bruges, 4. -7. July 2012. Veröffentlicht von Vrije Universiteit Brussel. Alle Rechte vorbehalten.