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BIOMECHANICS DISABILITY SWIMMING
Figure 3: Intra- cyclic speed curve of a breaststroke swimmer
swimming speed when pulling with their affected limb.
Figure 4: Intra- cyclic speed curve of a unilateral arm amputee front crawl swimmer
Application 2: Measuring streamlining ability The ability to streamline effectively during and after the push-off from the wall is an important aspect of turning performance. The velocity meter can be used to objectively evaluate a swimmer’s streamlining ability. Figure 5 shows the speed curve
Figure 5: Speed curve of a paralympic champion following a wall push-off
of a below knee amputee while gliding after a push-off. The slope (gradient) of the curve gives a direct measure of how well the swimmer is streamlining. In this example, the glide speed drops from 2 m/s to 1 m/s in 1.95 seconds. In another trial, in which the swimmer held his head too high, the corresponding time was 1.29 seconds, indicating poorer streamlining. Thus, the velocity meter allows the
coach to evaluate the effect that small adjustments to body position have on push-off performance and provide immediate feedback to the swimmer. It also enables the coach to monitor their swimmer’s progress on this aspect of turning performance throughout the season.
Figure 6a: Tethered force measurement
Tethered and semi-tethered force analysis Tethered swimming is a method of measuring an individual’s force production while they swim against a restraining tether (Figure 6a). The swimmer’s stroke-by-stroke force is measured using a force transducer mounted on the pool-side. The transducer is linked to a laptop PC via an AD-converter where the force trace is displayed in real time and then stored for analysis. An example of a tethered force curve is shown in Figure 6b.
Figure 6b: Force curve for four arm strokes
Tethered swimming force analysis is a useful method for quantifying the extent of bi-lateral asymmetry present in a swimmer’s front crawl and back crawl stroke. These asymmetries are very apparent in swimmers with partial uni-lateral amputations (arm or leg) but may also be present in swimmers who appear, from video, to have symmetrical strokes.
A number of tethered swimming protocols are currently being piloted with the aim of developing a swimming-specific test for anaerobic power. One such protocol involves a 30-second maximal effort fully tethered swim, from which a fatigue index is calculated using the linear regression of the tethered force-time function. Also under development is a semi- tethered device that will measure force under swimming conditions that are more ecologically valid than in the fully tethered swimming mode, as it allows swimmers to progress down the pool.
APPLIED RESEARCH PROJECTS
As there is a paucity of published research on the biomechanics of elite disability swimming, applied research has become an essential component of the biomechanics support project. This research is necessary to provide an evidence base for the assessment and intervention work. Applied research work is currently focusing on the performance optimisation of various disability groups. One example is presented here: swimmers with an upper limb amputation.
Swimmers with an upper limb amputation
There are currently ten swimmers on the World Class Pathway programme who have a single arm amputation at the level of the elbow. In addition to the velocity meter analysis and tethered force analysis that were described earlier in this paper, a number of other approaches are being used to determine the factors that limit the performance of this group of swimmers; these include 3D motion analysis, computational fluid dynamics (CFD) and isokinetic dynamometry.
3D motion analysis To obtain accurate information on the spatial movement patterns of the swimmers, three-dimensional motion analysis is used. Swimmers are video- taped using multiple, synchronised video cameras recording above and below water. The video recordings from each camera view are then digitised
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