It was calculated that 23 patients are required in order to detect a difference between means of 32.3 cm/s, as reported by Wirz , with a standard deviation of 37.5 cm/s, a power of 80% and a confidence level of 95% On the other hand, Hornby reported a difference between means of 0.36 m/s with a standard deviation of 0.14 m/s, which results on a sample size of 4 subjects per group.