Front Crawl Is More Efficient and Has Smaller Active Drag Than Backstroke Swimming: Kinematic and Kinetic Comparison Between the Two Techniques at the Same Swimming Speeds.

Tomohiro Gonjo,João Paulo Vilas-Boas,Ross Sanders,Hideki Takagi,Ricardo J Fernandes,Carla Mccabe,Kenzo Narita

doi:10.3389/fbioe.2020.570657

Abstract

The purpose of this study was to investigate differences in Froude efficiency (ηF) and active drag (DA) between front crawl and backstroke at the same speed. ηF was investigated by the three-dimensional (3D) motion analysis using 10 male swimmers. The swimmers performed 50 m swims at four swimming speeds in each technique, and their whole body motion during one upper-limb cycle was quantified by a 3D direct linear transformation algorithm with manually digitized video footage. Stroke length (SL), stroke frequency (SF), the index of coordination (IdC), ηF, and the underwater body volume (UWVbody) were obtained. DA was assessed by the measuring residual thrust method (MRT method) using a different group of swimmers (six males) due to a sufficient experience and familiarization required for the method. A two-way repeated-measures ANOVA (trials and techniques as the factors) and a paired t-test were used for the outcomes from the 3D motion analysis and the MRT method, respectively. Swimmers had 8.3% longer SL, 5.4% lower SF, 14.3% smaller IdC, and 30.8% higher ηF in front crawl than backstroke in the 3D motion analysis (all p < 0.01), which suggest that front crawl is more efficient than backstroke. Backstroke had 25% larger DA at 1.2 m⋅s–1 than front crawl (p < 0.01) in the MRT trial. A 4% difference in UWVbody (p < 0.001) between the two techniques in the 3D motion analysis also indirectly showed that the pressure drag and friction drag were probably larger in backstroke than in front crawl. In conclusion, front crawl is more efficient and has a smaller DA than backstroke at the same swimming speed.

Highlights

Competitive swimming techniques are categorized into alternating and simultaneous group
stroke frequency (SF), Stroke length (SL), ηF, and index of coordination (IdC) in front crawl were 3.5–7.7% lower, 5.9–11.9% longer, 28.6–33.7% larger, and 13.1–15.3% lower than in backstroke, respectively (Table 2), with no interaction between the techniques and trials. These results mean that swimmers achieved lower SF, longer SL, higher ηF, and lower IdC in front crawl than in backstroke to achieve the same v regardless of its magnitude
The purpose of this study was to assess the differences in ηF and DA between front crawl and backstroke using a 3D motion analysis and the measuring residual thrust (MRT) method, testing two hypotheses; ηF would be higher in front crawl than backstroke; DA would be similar between the two techniques

Summary

Introduction

Competitive swimming techniques are categorized into alternating (front crawl and backstroke) and simultaneous group (butterfly and breaststroke). Swimmers usually achieve a faster swimming velocity (v) in front crawl than in backstroke despite their similarity such as six-beat kick during each upper limb cycle, probably due to the energy expenditure difference at a given v (energy cost; C). A lower C in front crawl than backstroke at 1.0, 1.2, 1.4, and 1.6 m·s−1 has been reported (Barbosa et al, 2006) This was based on different groups of swimmers and potentially affected by anthropometric and skill level differences. To overcome this limitation, C of the two techniques has been compared using the same swimmers, and 15% lower value in front crawl than in backstroke, despite the similar stroke frequency (SF) and stroke length (SL), has been reported (Gonjo et al, 2018). C is expressed as the equation below (Di Prampero et al, 1974; Zamparo et al, 2011)

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Conclusion