The present study analyses the effects of anthropometric parameters (weight, height, wingspan, BMI, wingspan/height) on spatio-temporal parameters (speed, amplitude, frequency, swimming index) of the swimming cycle in a sprint crawl event. 40 swimmers (22 boys and 18 girls), all between 12 and 13 years of age, were first anthropometrically measured and then measured in the water by swimming a 25 m crawl start. The speed, frequency and amplitude were calculated by video analysis. The results showed that, in general, anthropometric parameters, especially height and wingspan, are determinant in sprint performance and in the amplitude of the swimming cycle, and that they have no relationship with swimming frequency.