Intra-cyclic Stroke Parameter Changes Associated With Increased Speed In Competitive Front-crawl Swimming

Abstract

Studies of stroke parameter relationships in swimming have shown that the basic strategy used by elite swimmers to increase speed is to increase stroke rate (SR) while attempting to maintain stroke length (SL). Recently, it has been shown that non-linear changes in SR and SL occur immediately after a swimmer reaches critical speed. The specific intra-cyclic mechanisms responsible for producing these changes, namely the duration of the propulsive and recovery phases of the stroke cycle, have not been investigated. PURPOSE: To determine temporal changes in the propulsion and recovery time associated with increased SR in front-crawl swimming. METHODS: Eight elite competitive swimmers (6 female, 2 male; 17.9 ± 0.86 yrs) performed a 4 x 200 m interval training set (60 s rest) in a 25 m pool according to target times that were based on a critical speed test (1 = submax. intensity, 2 = max. lactate steady state, 3 = critical speed, 4 = VO2 max.). Velocity, SR, SL, propulsion time and recovery time were recorded for each 25 m length of each 200 m repetition. The data were normalized (1st length %) to compare the relative stroke parameter changes between the 4 x 200s using repeated measures ANOVA. RESULTS: As speed increased, SR increased significantly (p < 0.05) for each repetition (+26.5 ± 7.8% from 1st to last repetition), whereas SL decreased significantly (p < 0.05) for the 3rd and 4th repetitions (-2.6 ± 1.6% & -4.8 ± 2.8%, respectively). In addition, SR increased markedly during the 3rd (critical speed) 200 (+12.0% vs. the previous increase of +3.4%). Changes in SR were associated with significant decreases (p < 0.01) in the propulsion time for each repetition (-25.6 ± 8.1% from the 1st to 4th repetition) as well as the recovery time (p < 0.05) for the 3rd and 4th repetitions (-6.9 ± 4.9% & -13.2 ± 5.7%, respectively). An asymmetric change in the stroke cycle was shown by a significant drop (p < 0.05) in the propulsion/recovery ratio from the 1st to 4th repetition (-9.3 ± 11.2%). CONCLUSION: Progressive speed related increases in SR are associated with simultaneous decreases in the duration of the propulsion and recovery phases of the stroke cycle, such that propulsion time decreases more than recovery time. This suggests that pulling/pushing the arm through the water faster contributes more to the elevation of SR than increasing the tempo of the recovery.