The assessment of path linearity in swimming: a pilot study

The lateral-medial displacement (LF) and the overall drift from a straight path (DT) were quantified and compared in 5 top-level (TLS) and 5 low-level (LLS) crawl swimmers. Sixteen repetitions of 25-m crawl at increasing intensity were performed and videotaped. The performances were divided into 3 intensities (< 80 %, 80 - 90 % and > 90 % of maximal speed). LF was expressed as overlength swum (OLS) and coefficient of variation (CV) of the Z-component movement. OLS revealed a significant main effect for swimmer level (p < 0.01), intensity (p < 0.01) and their interaction (0.48, 0.37, 0.31-m for TLS and 0.47, 0.43, 0.44-m for LLS, p < 0.05). CV was significantly higher in LLS at the lowest (0.69 vs. 0.22, p < 0.05) and highest intensity (0.71 vs. 0.33, p < 0.05). DT, expressed as the slope of the linear regression of position data vs. time, was significantly higher in LLS only at the highest intensity (0.025 vs. 0.013, p < 0.05). The amount of dissipated energy due to LF, quantified by means of discrete Fourier analysis, revealed a difference only when the 0 - 5 Hz and 5 - 10 Hz spectral windows were analysed separately. While LF has a practical significance since it contributes to increase drag, DT is negligible at least for short-distance events.