Producing propelling force in an efficient way in the right swimming direction is one of the key factors in competitive swimming. During the action the extremities of the swimmer give energy to the water molecules to accelerate them, to generate flow around and along the hand-arm complex to achieve the highest pressure difference in the right time and space. There are differences in morphological and physical characteristics between swimmers and there is an infinite number of possible motion variations to perform the crawl arm stroke. Difference should exist between swimmers, and in the way they can exploit the potential of the fluid environment. Direct force measurement is impossible during free swimming and the analitical investigations up to date did not provide a useful method to calculate the force production, therefore a special approach is necessary to express the level of the propelling ability. METHODS: 8 internationally recognised male swimmers (19,8 ±0,9 yrs, 73,9 ±6,0 kg, 181,7 ±5,5 cm) were asked to perform the non-breathing, only arm task on a special device which recorded the force (f=200). The legs were tied and supported. The starting frequency (FR) was set at f=0,5 Hz and was increased with f=0,083 Hz steps till the swimmer could maintain the stabil rhythm. 4 underwater cameras (50 Hz) were used to record the kinematic parameters and the APAS system was employed to calculate the 3D data for the analysis. Reference forces were calculated based on anthropometric and kinematic data with a 3-segment simple model concerning the drag equation without the C value and a projection to the swimming direction were related to the measured force data. The Pearson correlation was employed between the 100m sprint velocity and the result to test the suitability of the method. RESULTS: The main force at the starting FR were 50,6 ±21,9 N. The force production increased almost in a linear fashion and peaked at the f=0,65 Hz: 76,2 ±24,5 N and dropped considerably at the highest FR value. The ratio between the measured and the reference force at the starting FR: 2,04 ±0.68 the value is almost constant for the individuals across the FR increments, with a little peak around the 3rd step. Free swimming velocity was measured in 100m distance v=1.92 ±0.07 m/sec. The study showed significant correlation between the calculated ratio and the velocity swam in 100m (r=0.749, p<0.05). DISCUSSION: The measured force difference caused by the unsteady effects of this dinamic experimental setup showed a litle higher value as it was reported by other experimental and analitical studies (CFD), where the quasy-steady and unsteady effects were investigated. The result indicates that this method fits the requirement to estimate the propelling ability of individuals, whereas the result can provide the magnitude which can differentiate between swimmers but not the way they do it.
© Copyright 2009 14th annual Congress of the European College of Sport Science, Oslo/Norway, June 24-27, 2009, Book of Abstracts. Veröffentlicht von The Norwegian School of Sport Sciences. Alle Rechte vorbehalten.