This paper is based on the ISBS 2007 lecture honouring Geoffrey Dyson, a pioneer in putting sports science into practice. Although the term `rhythm` is frequently used by coaches, commentators, and participants in sports, it is rarely quantified. Using examples from analysis of butterfly and front crawl swimming the lecture described how rhythms may be quantified using Fourier analysis and presented `typical` results from past and current research. In combination with kinematic and kinetic data analysis of rhythms can provide an insight into what constitutes `good rhythm` in specific sports skills. Importantly, there is potential to use knowledge of rhythms. CONCLUSIONS: Having investigated the rhythms in butterfly and front crawl in combination with accurately derived kinematic and kinetic data some conclusions may be drawn. 1. Skilled butterfly swimming is characterised by 'rocking', that is, rotations about transverse axes, of body segments to yield wave-like undulations of shoulders, hips knees and ankles. 2. The undulations are coordinated to yield travelling 'body waves' to optimise performance from: a. A hydrodynamic perspective b. An energy transmission and re-use perspective. 3. The phase relationship between the one-beat H1 frequency and two-beat H2 is important to performance. 4. Skilled front crawl swimming using a 6 beat kick swimming is characterised by 'rolling' of body segments to yield wave-like rotations of shoulders, hips, knees and ankles. 5. The rolling actions are coordinated to yield a travelling 'torsional' wave from hip to ankles to optimise performance from a hydrodynamic perspective.
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