## 4 Discussion
### Experimental Results  
Most studies that analyze propulsive force in swimmers (as it relates to swimming velocity) tend to use the average of a given trial for further analysis [38; 40]; however, in sports, an intravariability occurs [41]. That is, athletes may not always reproduce a given motion in the exact same way. In swimming, this phenomenon may be even greater due to the unstable conditions of the aquatic environment [42]. Therefore, to have a deeper insight, researchers and coaches can measure a given variable in different swimming pool sections as it is done in a race analysis context [23] or in a stroke-by-stroke analysis during a given trial [21; 43]. In the present study, the researchers chose to analyze the variables between sections for convenience and because the sample consisted of recreational swimmers rather than high-level swimmers. The data revealed that the propulsive force of the swimmers in front-crawl did not differ between the sections and did not present a significant side effect (i.e., differences between right and left hand). The literature lacks information on the propulsive force variation during trials. Notwithstanding, [PERSON] et al. [17] observed that, at least in high-level swimmers, propulsive force at maximum swimming velocity tended to decrease in a stroke-by-stroke analysis. However, the authors [17] observed asignificant side effect (with a small effect size--based on the cut-off values of this study), which was not found in the present study. Therefore, based on sample demographics or other characteristics (such as dry-land strength or motor control), swimmers may or may not have a significant difference in the mean propulsive force between sides. This is a phenomenon that needs to be further studied, as well as its implications for swimming performance. The activity observed in swimming velocity (and remaining kinematic variables) was the same as in the propulsive force, i.e., it did not significantly change between sections. In maximal trials or official sprinting events, swimming velocity tends to decrease significantly throughout the trial or front-crawl race in trained swimmers [17; 23]. As this sample was composed of recreational swimmers, it seems that they presented an opposite profile when performing a maximal trial. As mentioned previously, swimming velocity and propulsive force did not change significantly between sections. The only variable that presented a significant difference between sections was the dv, in which a decrease was observed. The dv is considered an efficiency proxy, in which smaller values are usually related to better performances [14; 20]. However, such an assumption is based on the average values of the entire trial. New approaches in swimming research are arguing that smaller values observed in the dv, at least in front-crawl, may not always be related to better performances and vice-versa [21]. Although swimming with greater gross efficiency may lead to lower energy expenditure [44], it is argued that swimmers can use different patterns of stroke mechanics (related to swimming efficiency) to maximize swimming velocity, at least in maximal trials or events [21]. Indeed, it can be argued that, in maximal trials or sprint events, swimmers are not concerned about saving energy. Therefore, swimmers can adopt a strategy based on generating greater propulsive forces and less efficient technique [21]. The \(\mathrm{C_{Da}}\) also decreased slightly (but not significantly) between sections. As far as it is known, this is the first study that indicates the measurement of \(\mathrm{C_{Da}}\) within the same trial. It was previously reported that, during swimming, FSA changes [27; 45] and, consequently, active drag changes [27]. Therefore, it can be suggested that the \(\mathrm{C_{Da}}\) can also change during swimming. The data of this study corroborates this assumption.