Lee, J., Mellifont, R., Winstanley, J., & Burkett, B. (2008). Body roll in simulated freestyle swimming. International Journal of Sports Medicine, 29, 569-573.

This study analyzed the timing and sequence of body roll relative to the propulsive phase of elite freestyle swimmers (N = 11) on a custom built swim bench. Three dimensional kinematic data of the head, chest, and hips were collected and the effect of sex and breathing assessed following mixed modeling approach.

For the breathing stroke, there was a similar timing between males and females, with the head roll occurring at 30% and 28%, respectively, the chest at 42% and 43%, and the hips at 43% and 40% of the propulsive phase. Differences in timing for the non-breathing stroke were observed between the genders, with male hip roll occurring much earlier than females. Female hip and chest roll occurred almost simultaneously in the non-breathing stroke. The sequence of movement for the non-breathing arm strokes was the same for both sexes (hip, chest, head). A significant difference in timing and sequence pattern was found for the breathing stroke with the head preceding the movement of the hips and chest for both males and females. Maximal body roll angles for the chest and hips showed variations between gender and stroke type.

Implication. Distinct patterns of timing and sequence of body roll in simulated 100-m freestyle swimming were observed. Between breathing and non-breathing crawl strokes. The early head turn timing probably is troublesome because it would cause the body to be less stable and would increase drag on the swimmer due to disruption of the flow lines that exist in non-breathing strokes. It is possible that the greater flexibility in females fosters gender differences in the amount and timing of hip and chest roll. [Kicking tends to slow or retard hip roll. Since males are less buoyant in the back half of their structure, the need to kick harder and more to maintain a horizontal alignment could be hypothesized as a reason why male hips turn later than the chest.]

Reducing the disruption in timing and function by the breathing action would seem to be a technique feature that is worthy of emphasis.

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