Differences in kinematics and energy cost between front crawl and backstroke below the anaerobic threshold

The purpose of this study was to determine kinematic and energetic differences between front crawl and backstroke performed at the same aerobic speeds. Ten male competitive swimmers performed front crawl and backstroke at a pre-determined sub-anaerobic threshold speed to assess energy cost (through oxygen uptake measurement) and kinematics (using three-dimensional videography to determine stroke frequency and length, intra-cycle velocity fluctuation, three-dimensional wrist and ankle speeds, and vertical and lateral ankle range of motion). For detailed kinematic analysis, resultant displacement, the duration, and three-dimensional speed of the wrist during the entry, pull, push, and release phases were also investigated. There were no differences in stroke frequency/length and intra-cycle velocity fluctuation between the swimming techniques, however, swimmers had lower energy cost in front crawl than in backstroke (0.77 +/- 0.08 vs 0.91 +/- 0.12 kJ m(-1), p < 0.01). Slower three-dimensional wrist and ankle speeds under the water (1.29 +/- 0.10 vs 1.55 +/- 0.10 and 0.80 +/- 0.16 vs 0.97 +/- 0.13 m s(-1), both p < 0.01) and smaller ankle vertical range of motion (0.36 +/- 0.06 vs 0.47 +/- 0.07 m, p < 0.01) in front crawl than in backstroke were also observed, which indirectly suggested higher propulsive efficiency in front crawl. Front crawl is less costly than backstroke, and limbs motion in front crawl is more effective than in backstroke.