Becker, T., & Havriluk, R. (2010). Quantitative data supplements qualitative evaluations of butterfly swimming. A paper presented at the XIth International Symposium for Biomechanics and Medicine in Swimming, Oslo, June 16–19, 2010.

"Previous analyses of thousands of trials of synchronized underwater video and hand force data show a dramatic increase in force at the beginning of the butterfly pull immediately following two events: 1) when the hands first submerge below the level of the shoulders and 2) when elbow flexion begins. As both of these events are usually observable by a coach on a pool deck, quantitative data about these events may help coaches to better qualitatively assess technique. As the mechanical advantage increases with both shoulder extension and elbow flexion at the beginning of the pull, it is hypothesized that hand force will significantly increase with these events."

Four events were analyzed: 1) when the hands first submerged below the level of the shoulders, 2) when elbow flexion began, 3) when the hands first became medial to the elbows, and 4) when the hands passed perpendicularly below the shoulders. Female swimmers (N = 23) from three university teams were tested swimming butterfly over a 20 m course. Underwater video and hand force data were collected over the last 10 m. The average hand force over a one-tenth of a second interval before and after each event was calculated.

There was a significant increase in force for two events; when the hands first submerged below the level of the shoulders (18.0 N) and when elbow flexion began (14.6 N). There was no significant change in force when the hands first became medial to the elbows or when the hands passed perpendicularly below the shoulders. Ss required .36 seconds to submerge the hands below the shoulders out of the .81 seconds total time that the hands were underwater generating force.

Implication. Large increases in force when the hands first submerge below the level of the shoulders and when elbow flexion begins emphasize the importance of a mechanically advantageous angle at both the shoulder and elbow upon entry. Coaches can qualitatively evaluate swimmers to ensure they eliminate the wasted time that their hands are above the shoulders [when hands move out to the sides instead of repositioning] by adjusting the entry angle/width. Swimmers should begin elbow flexion as soon as the entry is completed. In addition to improving performance, these technique adjustments will be helpful in reducing shoulder injury.

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