The Influence of the Frontal Surface Area and Swim Velocity Variation in Front Crawl Active Drag

<p><b>Purpose:</b> The aims of this study were to 1) compare active drag (<i>D</i>_a) calculation between a single land-based measurement of frontal surface area (FSA) and in-water FSA measures obtained at key events of the arm pull (1, right upper-limb catch; 2, right upper-limb insweep; 3, right upper-limb exit and left upper-limb catch; 4, left upper-limb insweep; and 5, left upper-limb exit and right upper-limb catch) at front crawl swimming, and 2) compare mechanical power variables computed based on these two approaches. <b>Methods:</b> Seventeen swimmers (11, male; 6, female; 16.15 ± 0.94 yr old) were recruited. The FSA was measured based on two approaches: (i) nonvariation, that is, assuming a constant value, and (ii) variation, that is, calculated in each key event of the front crawl swim. Active drag based on a nonvariation of the FSA was measured using the Velocity Perturbation method. Active drag based on a variation approach was measured in each key event of the front crawl according to the law of linear motion. Paired <i>t</i>-test (<i>P</i> ≤ 0.05), simple linear regression models, and Bland–Altman plots between assessment methods (variation vs nonvariation) were computed. <b><i>Results:</i></b> The FSA (variation) was higher than when assuming a nonvariation (0.1110 ± 0.010 vs 0.0968 ± 0.010 m², Δ = 15.69%, <i>t</i> = 4.40, <i>P</i> < 0.001, <i>d</i> = 0.95). Active drag (variation) was also significantly higher than when assuming a nonvariation (88.44 ± 25.92 vs 75.41 ± 15.11 N, Δ = 16.09%, <i>t</i> = 3.66, <i>P</i> = 0.002, <i>d</i> = 0.61). <b>Conclusions:</b> Besides the FSA, swim velocity also changes during the front crawl arm pull. The variation of both variables had a significant effect on the active drag measurement and consequently on mechanical power and total power input variables.</p>