Stroke symmetry : implications on thrust production in elite swimmers

Abstract

Background: Technique plays a key role in a swimmer’s ability to generate propulsive force in the pool. A technique used by many middle distance freestylers is a “semi-catch up” stroke. Practitioners call in “lopsided” or “gallop”, while in academia, it is known as an asymmetrical stroke. A frequently discussed topic between coach and swimmer is whether swimming with an asymmetrical stroke is better than swimming with a symmetrical stroke. Aims & Hypothesis: This research aims to investigate the implications that stroke symmetry has on thrust production and kinematics in the upper limbs when swimming at a sub-maximal pace. It is hypothesized that swimming with an asymmetrical stroke requires less force output from the upper limbs to achieve a faster time in the pool as compared to a symmetrical stroke. Methods: 10 elite swimmers from Singapore’s National Training Centre were recruited for this research. In a randomized crossover design, participants attended 2 separate sessions, where they swam 4x25m at a 200m pace; each time with either a symmetrical or asymmetrical stroke. Data for hand pressure and swim velocity were captured using the Aquanex Swim Analysis and Swim Speedometer respectively at a sampling frequency of 50Hz. Data was analysed by running a paired t-test. Results: No statistically significant results were found between swimming with an asymmetrical stroke and symmetrical stroke. However, with the use of an excel spreadsheet for measuring clinical effect likelihood, it was suggested that swimming with an asymmetrical stroke instead of a symmetrical stroke could potentially be beneficial. Conclusion: It is suggested that swimming with an asymmetrical stroke has little to no implications on a swimmer’s speed compared to swimming with a symmetrical stroke. However, an asymmetrical stroke required less force output from the upper limbs to achieve a similar speed as a symmetrical stroke, potentially allowing swimmers to swim more efficiently when swimming at a sub-maximal pace.