The effect of water height on stride frequency, stride length and heart rate during water treadmill exercise

Reasons for performing study: Water treadmill exercise is often incorporated into rehabilitation programmes for horses yet little is known about the biomechanical and physiological responses to water walking. Objectives: To establish whether stride frequency (SF) reached steady state as a result of 6 introductory water treadmill sessions and then to investigate the effect of increasing water height on SF, stride length (SL) and heart rate (HR). Methods: Nine horses with no previous experience of water treadmills completed 6 sessions of walking for between 15 and 30 min. Each horse was fitted with a leg mounted accelerometer to measure SF. The effect of session on SF was tested using univariate ANOVA. Eight horses completed 3 further sessions at each of the following water heights; proximal interphalangeal joint (PIP), carpus and ulna. SF, SL and HR at each water height were compared to a control (hoof height) using univariate ANOVA. Results: When SF during introductory sessions 4–6 were compared, there was no significant effect of session on SF (P>0.05). In the second part of the experiment, SF was 0.57 ± 0.03 strides/s at control, 0.54 ± 0.03 strides/s at the PIP joint, 0.51 ± 0.02 strides/s at the carpus and 0.52 ± 0.03 strides/s at the ulna. Stride frequency at carpal and ulna height was significantly lower than at control (P<0.05). Stride length was 1.53 ± 0.09 m for control, 1.63 ± 0.10 m at the PIP joint, 1.71 ± 0.08 m at the carpus and 1.68 ± 0.10 m at the ulna. Stride length at carpal and ulna height was significantly greater than control (P<0.05). There was no significant difference between HR during control and any other water height (P>0.05). Conclusion: Horses reached steady state gait within the first 6 sessions of water treadmill exercise. Walking in water at the level of the carpus or ulna resulted in a lower SF compared to walking in water at hoof height.