STROKE RATE INCREASES ARE ASSOCIATED WITH SHORTENED DURATION OF THE UNDERWATER PROPULSIVE PHASE (I.E., GREATER ACCELERATION)
Barden, J. M., Kell, R. T., & Kobsar, D. (2009). Intra-cyclic stroke parameter changes associated with increased speed in competitive front-crawl swimming. ACSM 56th Annual Meeting, Seattle, Washington. Presentation number 2571.
This study determined temporal changes in the propulsion and recovery stroke-phase times associated with increased stroke rate in front-crawl swimming. Elite competitive swimmers (M = 2; F = 6) performed a 4 x 200 m interval training set (60 seconds 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 = VO2max). Velocity, stroke rate, stroke length, propulsion time, and recovery time were recorded for each 25-meter length of each 200-meter repetition.
As speed increased, stroke rate increased significantly for each repetition, whereas stroke length decreased significantly for the third and four repetition conditions. Stroke rate increased markedly during the third (critical speed) repetition. Changes in stroke rate were associated with significant decreases in the propulsion time for each repetition as well as the recovery time for the third and fourth repetitions. An asymmetric change in the stroke cycle was shown by a significant drop in the propulsion/recovery ratio from the first to fourth repetition.
Implication. Progressive speed related increases in stroke rate 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 stroke rate than increasing the tempo of the recovery. [It should be noted that shorter propulsion time usually indicates greater acceleration in the propulsive phase of the stroke.]
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