Front-crawl stroke descriptors variability assessment for skill characterisation.

Area of Science:

• Sports Science
• Biomechanics
• Swimming Performance Analysis

Background:

• Front-crawl swimming skill is complex, involving intricate technique descriptors.
• Understanding technique variability is crucial for differentiating skill levels and predicting performance.

Purpose of the Study:

• To characterize front-crawl swimming skill by analyzing the variability patterns of technique descriptors.
• To identify reliable metrics for assessing swimming technique stability and motor pattern repeatability.

Main Methods:

• Nine national and nine recreational swimmers performed front-crawl trials at varying intensities (70%, 80%, 90% of personal best).
• Wearable inertial measurement units (IMUs) and validated algorithms assessed technique descriptor variability per arm cycle.
• Key metrics included phase durations, index of coordination (IdC), stroke length, stroke rate, intra-cyclic velocity variation, and the Cauchy index for technique stability.

Main Results:

• Skilled swimmers achieved higher velocities at similar intensities with more stable motor patterns (smaller Cauchy index).
• The similarity of intra-cyclic velocity variation across intensities indicated a wider dynamic range in skilled swimmers.
• A new metric, cycle velocity variation, was introduced and found to correlate with the Cauchy index (r=0.72, P<0.01).

Conclusions:

• The index of coordination (IdC) is a performance predictor mainly for swimmers of similar expertise.
• Intra-cyclic velocity variation and cycle velocity variation are essential for studying motor adaptations to new constraints in swimming.