Effect of water depth on limb kinematics of the domestic dog (Canis lupus familiaris) during underwater treadmill exercise

Canine hydrotherapy is an increasingly popular modality for the rehabilitation of dogs; however, little evidence exists to support the use of current hydrotherapy protocols. Before data can be meaningfully collected from pathological animals, biomechanical data for healthy animals is required. Kinematic analysis was utilised to observe the effect of increasing water depth on the stride parameters (including duty factor) of dogs exercising on a canine hydrotherapy treadmill. During two sessions, eight clinically sound adult dogs walked on the underwater treadmill at four different water depths (dry, mid-tarsal, between the lateral malleolus and the lateral epicondyle, and between the lateral epicondyle and greater trochanter). Reflective kinematic markers were placed onto anatomical limb landmarks and a video camera was used to record foot contacts at 60 Hz. Data were digitised using video analysis software and stride length, stride frequency and duty factor were subsequently calculated. Data were analysed using the Friedman Test and Wilcoxon post hoc pairwise tests to identify differences between conditions. There was a significant effect of water depth on duty factor (P<0.0005). Hind limb duty factor differed significantly from fore limb duty factor (P<0.0005), except at the depth between the lateral malleolus and the lateral epicondyle where no significant difference was observed. There was a significant effect of water depth on both stride frequency (P<0.0005) and stride length (P<0.0005). In summary, water depth has a significant impact on the stride parameters of dogs exercising on the canine hydrotherapy treadmill and as such is an important consideration when designing underwater treadmill based rehabilitation programs.