, Volume 94, Issue 5-6, pp 697-704

Energy cost of swimming of elite long-distance swimmers

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The aim of this study was: (1) to assess the energy cost of swimming (C s, kJ km−1) in a group of male (n=5) and female (n=5) elite swimmers specialised in long-distance competitions; (2) to evaluate the possible effect of a 2-km trial on the absolute value of C s. C s was assessed during three consecutive 400-m trials covered in a 50-m pool at increasing speeds (v 1, v 2, v 3). After these experiments the subjects swam a 2-km trial at the 10-km race speed (v 2km) after which the three 400-m trials were repeated at the same speed as before (v 5=v 1, v 6=v 2, v 7=v 3). C s was calculated by dividing the net oxygen uptake at steady state \(({\dot{V}}{\text{O}}_{2{\text{ss}}})\) by the corresponding average speed (v, m s−1). \({\dot{V}}{\text{O}}_{2{\text{ss}}}\) was estimated by using back extrapolation technique from breath-to-breath \({\dot{V}}{\text{O}}_2\) recorded during the first 30 s of recovery after each test. C s increased (from 0.69 kJ m−1 to 1.27 kJ m−1) as a function of v (from 1.29 m s−1 to 1.50 m s−1), its values being comparable to those measured in elite short distance swimmers at similar speeds. In both groups of subjects the speed maintained during the 2-km trial (v 2km) was on the average only 1.2% faster than of v 2 and v 6 (P>0.05), whereas C s assessed at the end of the 2-km trial (v 2km) turned out to be 21±26% larger than that assessed at v 2 and v 6 (P<0.05); the average stroke frequency (SF, cycles min−1) during the 2-km trial turned to be about 6% (P<0.05) faster than that assessed at v 2 and v 6. At v 5, C s turned out to be 19±9% (P<0.05) and 22±27% (0.1<P=0.05) larger than at v 1 in male and female subjects (respectively). SF was significantly faster (P<0.05, in male subjects) and the distance per stroke (Ds=v/SF) significantly shorter (P<0.05) in female subjects at v 5 and v 6 than at v 1 and v 2. These data suggest that the increase of C s found after the 2-km trial was likely related to a decrease in propelling efficiency, since the latter is related to the distance per stroke.