A mechanical speedo-meter to assess swimmer’s horizontal intra-cyclic velocity: validation for breaststroke and butterfly stroke

The aim was to validate a system to assess speed-fluctuation at breaststroke and butterfly stroke. 12 boys and 11 undertook a set of maximal 2x25 m swims (Breaststroke and Butterfly stroke). The speedo-meter cable was attached to the subject’s hip and data was acquired on-line. At the same time, subjects were recorded in the sagital plane with an underwater video camera enabling the hip to be digitized. The following were analysed: (i) maximal velocity; (ii) minimal velocity; (iii) difference between maximal and minimal velocity; (iv) coefficient of variation. There were no significant differences for the mean values between methods, except for the coefficient of variation. Linear regression models were highly related. More than 80% of the Bland-Altman plots were within the 1.96 standard-deviation criteria used as a rule of thumb for technique validation.