Conor Osborough and Mike Peyrebrune had some interesting and perhaps unexpected findings when looking at the effects of fatigue on the technique of national level youth male butterfly swimmers. First, unlike freestyle in which stroke length decreases with fatigue, stroke length was maintained. Naturally then, as speed decreased the stroke frequency decreased with all phases of the stroke taking longer. But there was no obvious 'falling apart' of the timing. Not surprisingly, as many of us have witnessed, the body becomes a bit less level - but only during the recovery phase. Also unlike freestyle, the hand trajectory was not obviously affected. However, elbow flexion and extension were both reduced reflecting a decreasing ability to use the elbow flexors and extensors to apply force. The authors suggested that maintaining form in butterfly to minimise resistive drag during recovery might be linked to encouraging swimmers to accelerate the hands outwards during the upsweep while maintaining a more horizontal trunk position and a lower/faster arm recovery.

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Osborough, C., Peyrebrune, M. (2006). The influence of repeated sprinting on the kinematics of butterfly swimming. In J.P. Vilas-Boas, F. Alves, A. Marques (eds.) Xth International Symposium on Biomechanics and Medicine in Swimming, University of Porto, Porto, June, 2006. pp70-73.

Per-Ludvik Kjendlie and his Scandinavian colleagues have found that the best swimmers use a strategic model in which stroke frequency decreases in the beginning of the race and then increases at the end of the 100m race whereas less successful have a fast SR to begin with and then decrease. The former strategy compensates for decreasing stroke length at the end of the race. The discussion is interesting in that the authors raise issues of whether the pattern of the less successful performers is actually strategic or a result of increasing fatigue that may be greater than the fatigue of the best swimmers in the latter stages of the race.

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Kjendlie, P., Haljand, R., Fjortoft, O., Stallman, R.K. (2006).Stroke frequency strategies of international and national swimmers in 100m races. In J.P. Vilas-Boas, F. Alves, A. Marques (eds.) Xth International Symposium on Biomechanics and Medicine in Swimming, University of Porto, Porto, June, 2006. pp52-54.

The debate goes on - is an 'S' shaped pattern advantageous in swimming? While analysis of the underwater paths of the hand during the propulsive phases is mostly backwards and the adage that 'good swimmers are good scullers' has fallen out of favour, the work of Kamata and colleagues at The University of Tsukuba could prompt another rethink. Using particle image velocimetry (PIV), which in layman's terms basically means tracking the motion of water and quantifying how fast it is moving, they have shown that direction changes produce a 'jet flow' that is propulsive. Rather than 'sculling' per se which was long believed to generate lift in the swimming direction through mechanisms such as the Bernoulli effect in which the force is greatest during the fastest part of the scull, the greatest propulsion may actually occur when the hand is moving quite slowly, that is during changes in direction. While it is probably not wise to advocate large sweeping sculls, it does appear that subtle direction changes play a very important role in optimising propulsion. Certainly PIV is enabling scientists to hone in on how propulsion is produced. The jet flow produced through the formation and shedding of vortices seems to be an important mechanism in human swimming. PIV will assist us to pin down the characteristics of good underwater stroke technique. In the meantime, we should continue to encourage 'feel for the water' and recognise the role of direction changes of the hand in generating propulsion in an efficient manner.

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Kamata, E., Miwa, T., Matsuuchi, K., Shintani, H., and Nomura, T. (2006). Analysis of sculling propulsion mechanism using two components particle image velocimetry. In J.P. Vilas-Boas, F. Alves, A. Marques (eds.) Xth International Symposium on Biomechanics and Medicine in Swimming, University of Porto, Porto, June, 2006. pp50-52.

A paper by Caty and several French and Italian collaborators presented at the 2006 Biomechanics and Medicine in Swimming conference has some interesting and important implications for training. An analysis of muscle activity of international swimmers performing 4*50m max sprint tests with 10s rests revealed that the wrist flexors and extensors fatigue considerably. Could this be a contributing factor to 'slipping water' in the last lap of a 200m race? The findings may indicate a need to include some dry land training to develop the local strength and endurance of the wrist flexors and extensors.

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Caty, V., A.H. Rouard, F.Hintzy, Y.A. Aujouannet, F. Molanari, M. Knaflitz. (2006). Time-frequency parameters of wrist muscles EMG after an exhaustive freestyle test. In J.P. Vilas-Boas, F. Alves, A. Marques (eds.) Xth International Symposium on Biomechanics and Medicine in Swimming, University of Porto, Porto, June, 2006. pp28-30.