A Biophysical Analysis on the Arm Stroke Efficiency in Front Crawl Swimming: Comparing Methods and Determining the Main Performance Predictors

Purpose: to compare different methods to assess the arm stroke efficiency (?_F ), whenswimming front crawl using the arms only on the Measurement of Active Drag System (MADSystem) and in a free-swimming condition, and to identify biophysical adaptations to swimming onthe MAD System and the main biophysical predictors of maximal swimming speed in the 200 mfront crawl using the arms only (?_200m). Methods: fourteen swimmers performed twice a 5 × 200 mincremental trial swimming the front crawl stroke using the arms only, once swimming freely, andonce swimming on the MAD System. The total metabolic power was assessed in both conditions.The biomechanical parameters were obtained from video analysis and force data recorded on theMAD System. The ?_F was calculated using: (i) direct measures of mechanical and metabolic power(power-based method); (ii) forward speed/hand speed ratio (speed-based method), and (iii) thesimplified paddle-wheel model. Results: both methods to assess ?_F on the MAD System differed (p< 0.001) from the expected values for this condition (?_F = 1), with the speed-based method providingthe closest values (?_F~0.96). In the free-swimming condition, the power-based (?_F~0.75), speedbased(?_F~0.62), and paddle-wheel (?_F~0.39) efficiencies were significantly different (p < 0.001).Although all methods provided values within the limits of agreement, the speed-based methodprovided the closest values to the "actual efficiency". The main biophysical predictors of ?_200mwere included in two models: biomechanical (R² = 0.98) and physiological (R² = 0.98). Conclusions:our results suggest that the speed-based method provides the closest values to the "actual ?_F" andconfirm that swimming performance depends on the balance of biomechanical and bioenergeticparameters.