Freestyle Arm Entry Effects on Shoulder Stress, Force Generation, and Arm Synchronization
Ted Becker, Everett Pacific Industrial Rehabilitation, USA
Rod Havriluk, Swimming Technology Research, USA
Previous research showed that immediately after the arm entry, female butterfly swimmers wasted time (30% of the stroke cycle) with their arms in a weak position that stressed their shoulders (Becker & Havriluk, 2010). The present study was designed to examine the prevalence of an ineffective arm entry in freestyle with respect to gender and the impact on shoulder stress, force generation, and arm synchronization.
The study included 40 university swimmers (20 males and 20 females), each tested with Aquanex+Video swimming freestyle over a 20 m course. At the completion of the arm entry, the position of the hand with respect the depth of the shoulder was determined. Stroke cycles were analyzed to determine the time that hand force generation begins (HFB) and ends (HFE) and the time that the hand submerged below the level of the shoulder (HSS). The arm synchronization was analyzed in terms of the gap or overlap between hands in force generation as HFE – HFB and HFE – HSS.
Most females (70%), but only 10% of males completed the arm entry with the hand closer to the surface than the shoulder. The time required to submerge the hand below the level of the shoulder (or time of exposure to shoulder stress) for females was significantly longer than for the males (p<.05). Males and females had a similar force overlap for HFE – HFB. For HFE – HSS; males had an overlap, but females had a gap.
The arm entry difference resulted in a much longer time of exposure to shoulder stress for the females. Because the females required so much time to submerge the hand below the shoulder, the arm synchronization showed a gap in force generation as opposed to an overlap for the males. Females can improve their arm entry to minimize time of exposure to shoulder stress and maximize the force generation overlap.
Becker, T.J., & Havriluk, R. (2010). Quantitative data supplements qualitative evaluation of butterfly swimming. In P-L. Kjendlie, R. K. Stallman, & J. Cabri (Eds.) Biomechanics and Medicine in Swimming XI. Norwegian School of Sport Science, Oslo.