  The present study analyzes the changes in acceleration produced by swimmers
before and after fatiguing effort. The subjects (n=15) performed a 25-meter
crawl series at maximum speed without fatigue, and a second series with
fatigue. The data were registered with a synchronized system that consisted in
a position transducer (1 kHz) and a video photogrametry (50Hz). The
acceleration (ms-2) was obtained by the derivative analysis of the variation of
the position with time. The amplitude in the time domain was calculated with
the root mean square (RMS); while the peak power (PP), the peak power frequency
(PPF) and the spectrum area (SA) was calculated in the frequency domain with
Fourier analysis. On one hand, the results of the temporal domain show that the
RMS change percentage between series was 67.5% (p<0.001). On the other hand,
PP, PPF, and SA show significant changes (p<0.001). PP and SA were reduced by
63.1% and 59.5%, respectively. Our results show that the acceleration analysis
of the swimmer with Fourier analysis permits a more precise understanding of
which propulsive forces contribute to the swimmer performance before and after
fatigue appears.
