How does muscle activity change with water depth in dogs walking on an underwater treadmill?

Canine rehabilitation is a rapidly developing area of veterinary medicine with an increasing range of techniques such as physical therapy, massage and hydrotherapy becoming widely available. The aim of these therapies is to restore animals to full health post-operatively, manage long-term conditions and promote fitness. Equine and canine kinematic research has found a relationship between water depth and kinematic parameters, however, there is limited research assessing the change in muscle activity with increasing water depth. The aim of this study was to investigate the impact of water depth on the muscle activity of dogs when walking on an underwater treadmill (UWT). Surface electromyography was used to assess muscle activity of the gluteus medius (GM) and longissimus dorsi (LD) of clinically sound dogs (n = 7) that were habituated to the UWT. Muscle activity was recorded at water depths of no submersion, above the tarsus, above the stifle and the midpoint between the stifle and the greater trochanter. Kinematic measurements were performed to calculate motion cycle sequencing. There was a significant decrease (p<0.01) in muscle activity between the depth above the tarsal and depths above the stifle, and at the midpoint between the tarsal and the greater trochanter in both the GM and LD. This suggests that UWT exercise at a water depth directly above the tarsal results in the greatest GM and LD muscle activity. These findings may help to inform future exercise and rehabilitation protocols for UWT exercise in dogs.