Upper body kinematic differences between maximum front crawl and backstroke swimming.

The purpose of this study was to investigate why front crawl is faster than backstroke from a kinematic perspective. Three-dimensional kinematics were obtained from one upper-limb cycle of ten male competitive swimmers performing 50 m front crawl and backstroke trials at maximum speed. Swimmers achieved faster centre of mass velocity in front crawl than backstroke (1.70 ± 0.04 vs 1.54 ± 0.06 m·s-1; p < 0.01) with no difference in stroke length (2.00 ± 0.25 vs 2.07 ± 0.17 m·cycle-1), while stroke frequency in front crawl was higher than that in backstroke (51.67 ± 6.38 vs 44.81 ± 4.68 cycles·min-1; p < 0.01). Maximum shoulder roll angle in front crawl was larger than that in backstroke (52.88 ± 4.89 vs 49.73 ± 5.73°; p < 0.05), while swimmers had smaller maximum hip roll in front crawl than backstroke (33.79 ± 6.07 vs 39.83 ± 7.25°; p < 0.05). Absolute duration of the release phase (from the last backward movement to the exit from the water of the wrist) and relative duration of the recovery phase were shorter in front crawl than backstroke (0.07 ± 0.03 vs 0.26 ± 0.08 s; p < 0.01, and 28.69 ± 2.50 vs 33.21 ± 1.43%; p < 0.01, respectively). In conclusion, front crawl is faster than backstroke because of its higher stroke frequency due to the shorter absolute release phase and relative recovery phase durations.