# How Should the Transition from Underwater to Surface Swimming Be Performed by Competitive Swimmers?
## 4 Discussion
### Pre-Transition Phase  
Before swimmers emerged from underwater, during the last underwater kicking cycle (pre-transition phase), the body position parameters (depth and inclination) did not statistically predict the forward velocity. At this point, only the kicking parameters (kicking length and rate) were correlated with velocity (Figure 2) and this highlighted the importance of kicking propulsion rather than technical position of the body underwater [34]. Values of kicking kinematics during pre-transition were similar to those obtained in USS by [PERSON] et al. [22; 23], [PERSON] et al. [35] and [PERSON] et al. [36] although the magnitude of correlations with forward velocity were in line with previous research [23] both for the kicking rate (\(r=0.519\) compared to \(r=0.383\) in the present research) and kicking length (\(r=0.630\) compared to \(r=0.552\)). The kicking amplitude, on the other hand, did not present statistical relationships with pre-transition velocity.  
The body position parameters on the pre-transition phase were between 6\({}^{\circ}\) and 16\({}^{\circ}\) for the body inclination (respect to horizontal) and from \(-0.36\) m (butterfly) to \(-0.62\) m (backstroke) for the body depth (Table 1). These inclinations were in line with previous data from [PERSON] et al. [22] who reported body angles of 17\({}^{\circ}\) degrees during USS. However, the pre-transition body depth was obviously lower than the optimum (from \(-0.74\) to \(-1.03\) m) for UUS [24]. These data, interestingly, suggest that, when transiting for underwater to  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Dependent Variables** & \multicolumn{4}{c}{**Backward Regression Model**} \\  & **Front Crawl** & **Backstroke** & **Butterfly** & **Breaststroke** \\ \hline Beta standardized & & & & \\ coefficients & & & & \\ Body depth & 0.32 & \(-0.40\) & 1.80 & 0.28 \\ Trunk inclination 1 & \(-0.36\) & 0.32 & & \\ Body inclination 1 & 0.38 & \(-0.30\) & & \\ DRP1 & & 0.33 & \(-0.52\) & 0.82 \\ DRP2 & \(-0.35\) & & 0.62 & \(-0.49\) \\ y-intercept (constant) & \(1.67\pm 0.08\) & \(1.92\pm 0.12\) & \(1.69\pm 0.08\) & \(1.25\pm 0.07\) \\ R\({}^{2}\) & 0.263 & 0.321 & 0.364 & 0.230 \\ R\({}^{2}\) adjusted & 0.154 & 0.213 & 0.293 & 0.125 \\ Standard error of estimate & 0.161 & 0.178 & 0.152 & 0.111 \\ F & 2.407 & 2.959 & 5.141 & 2.191 \\ P & 0.044 * & 0.039 * & 0.006 ** & 0.118 \\ Number of observations & 30 & 30 & 30 & 30 \\ \hline \hline \end{tabular} Note: beta standardized coefficients presented for independent variables where \(p<0.05\).  
\end{table}
Table 2: Backward regression analysis of the transition phases in all four strokes.  
surface swimming, swimmers diminish depth but maintain body inclinations with a correct alignment almost parallel to water surface, not different from the UUS [15]. Otherwise, there would be an increase in frontal drag [7] with a concomitant velocity reduction [37]. As previously mentioned, the body position parameters presented small or no correlations with pre-transition velocity. However, the direction of relationships for the body depth depended on strokes (Figure 2). In backstroke, where body depth was greatest, negative correlation between depth and forward velocity were detected. On the other hand, in the ventral techniques (where body depth was lower) greater depths were related to faster velocities. This highlighted the stroke-dependent strategies when transiting from underwater to surface swimming.