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 examined the prevalence of an ineffective arm entry in freestyle with respect to gender. The study also examined the arm entry impact on shoulder stress, force generation, and arm synchronization.
Method
The study included 40 university swimmers (20 males and 20 females). Each swimmer was tested with Aquanex 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. An analysis of stroke cycles determined the time that hand force generation begins (HFB) and ends (HFE). An analysis also showed the time to submerge the hand 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.
Results
Most females (70%), but only 10% of males completed the arm entry with the hand closer above the shoulder. The time required to submerge the hand below the level of the shoulder was the time of exposure to shoulder stress (ET). The ET for females was significantly longer than the ET for 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.
Conclusions
The arm entry difference resulted in a much longer time of exposure to shoulder stress for the females. The females required so much time to submerge the hand below the shoulder so there was a gap in force generation. The males had an overlap in force generation. Females can improve their arm entry to minimize time of exposure to shoulder stress and maximize the force generation overlap.
References
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.
