animal therapy magazine

Canine Hydrotherapy

How does water depth affect muscle activity when dogs walk on a water treadmill?

by Dr Alison Wills, Department of Animal and Agriculture, University Centre Hartpury, Hartpury, Gloucestershire

As canine hydrotherapy gains popularity for the rehabilitation of a range of different conditions, questions are beginning to arise surrounding the type of protocol that is implemented for individual dogs. Some dogs referred for hydrotherapy will swim in a pool, some will walk on a water treadmill and some may undergo a combination of both approaches. If the treatment team including the attending veterinarian, hydrotherapist and or physiotherapist determine that water treadmill walking will be beneficial for the rehabilitation of a particular animal, they need to specify the exact nature of the aquatic exercise the dog will perform. There any many things that can be varied on a water treadmill including the speed and incline of the belt as well as the water depth. While speed is usually based on the comfortable walking speed of the animal, (which may vary based on breed and level of fitness), the most appropriate water depth for individual cases may be more difficult to ascertain.

What are the benefits of hydrotherapy?

The majority of research conducted to date has assessed the benefit of hydrotherapy for dogs with a range of different clinical conditions. Studies have shown that an increased range of movement is exhibited by dogs not only during swimming (Marsolais et al., 2003) but also after the completion of a single session of hydrotherapy (Preston and Wills, 2018) and

following a programme including water treadmill exercise (Monk et al., 2006). Based on existing knowledge that an increase in range of movement can relieve pain and improve general limb function, these studies are promising and demonstrate that hydrotherapy really can benefit dogs suffering from a range of musculoskeletal problems.

How does gait change when walking on a water treadmill?

Few studies have focussed specifically on how dogs move during aquatic walking or have made recommendations for the design of water treadmill protocols. However, it has been demonstrated that water depth can affect the way a dog moves on a water treadmill; with an increased water depth resulting in a longer stride length and decreased stride frequency (Barnicoat and Wills, 2016).While these data are useful in helping to further our understanding of the mechanics of canine aquatic locomotion, they fail to provide specific information about how these changes might reflect adaptations in muscular function. As dogs are a terrestrial quadruped, their movement in water has not been extensively studied and data on their overground locomotion may lack applicability to their movement in water. Therefore, until recently, our understanding of how water depth might affect muscle activity in dogs walking on a water treadmill was limited.

How does water depth affect muscle activation on a water treadmill?

Parkinson and colleagues (2018) investigated the effect of altered water depth on the activation of two muscles, the longissimus dorsi (LD) and the gluteus medius (GM). Whilst little is known about the role of the epaxial musculature in dogs, the LD has been shown to maintain stability of the vertebral column during locomotion in horses (Licka, Peham and Frey, 2004). Similarly, studies investigating the canine caudal musculature are limited, but the GM is involved in the initiation of movement in dogs (Williams et al., 2008). The authors used seven clinically healthy dogs of a variety of breeds in the study and used surface electromyography (EMG) sensors (a special type of surface sensor which measures muscle activity) to examine how the two muscles were activated when the dogs walked in water of a variety of depths. Results indicated that there was a significant effect of water depth on the activation of both muscles studied (Parkinson et al., 2018). Overall, it was found that water at tarsal height elicited the most muscular action, suggesting that this depth might be more appropriate later in the rehabilitation process when the patient requires further challenge. The authors recommended that higher water levels might be more appropriate for the early stages of canine rehabilitation but cautioned practitioners to consider the clinical history and fitness levels of individual dogs when designing rehabilitation programmes.

Is there an effect of laterality on muscle activation?

Interestingly, the activity of the GM and LD was asymmetrical in the dogs included in the study. The reasons for this were unclear, the dogs may have had a dominant limb (Garcia et al., 2014) or they may have been bending their body while walking on the water treadmill. It is also possible that the dogs had a small degree of pathology, which was insufficient for them to show clinical signs, but did result in the uneven muscle activation observed. Consequently, it is important that practitioners are aware of the potential influence of the handler at the front of the water treadmill and check that their position does not influence the straightness of the dog during exercise. Parkinson and colleagues recommended that the hydrotherapist should try to ensure the dog remains straight during sessions on the water treadmill to avoid unintentional asymmetrical muscle use.

Why does water depth affect the way muscles are activated during water treadmill walking?

Water depths above the stifle decreased the estimated workload of the GM compared to walking on a dry treadmill. If dogs adapt their limb movement as described by Barnicoat and Wills (2016) to push the hindlimb through deeper water, then this, along with the effect of buoyancy would reduce the work the GM needs to perform. It is thought that in deeper water, dogs lift their pelvic limb higher increasing the time the limb is elevated above the treadmill belt. As this movement is assisted by buoyancy, this may be a more energy efficient movement pattern needing less input from the GM. The effect of water depth on the LD was similar, but the differences between water depths were smaller. Whilst there are no studies that have investigated movement of the canine spine during aquatic locomotion, the results are consistent with the role of the LD in maintaining stability during walking.


It is clear that further research is required to fully understand how water depth affect muscle activation in dogs walking on a water treadmill. However, this preliminary study suggests that water depth plays an important role in the activation of specific muscles. In addition, research examining the way aquatic locomotion affects the movement of the canine spine would be invaluable in understanding how water depth can be better used to tailor rehabilitation programmes to individual patients.


Barnicoat, F. and Wills, A. P. (2016) ‘Effect of water depth on limb kinematics of the domestic dog (Canis lupus familiaris) during underwater treadmill exercise’, Comparative Exercise Physiology, 12(4), pp. 199– 207. doi: 10.3920/CEP160012.

Garcia, T. C. et al. (2014) ‘Forelimb brachial muscle activation patterns using surface electromyography and their relationship to kinematics in normal dogs walking and trotting’, Comparative Exercise Physiology. Wageningen Academic Publishers, 10(1), pp. 13–22.

Licka, T. F., Peham, C. and Frey, A. (2004) ‘Electromyographic activity of the longissimus dorsi muscles in horses during trotting on a treadmill’, American journal of veterinary research. Am Vet Med Assoc, 65(2), pp.155–158.

Marsolais, G. S. et al. (2003) ‘Kinematic analysis of the hind limb during swimming and walking in healthy dogs and dogs with surgically corrected cranial cruciate ligament rupture’, Journal of the American Veterinary Medical Association. Am Vet Med Assoc, 222(6), pp. 739–743.

Monk, M. L., Preston, C. A. and McGowan, C. M. (2006) ‘Effects of early intensive postoperative physiotherapy on limb function after tibial plateau leveling osteotomy in dogs with deficiency of the cranial cruciate ligament’, American journal of veterinary research. Am Vet Med Assoc, 67(3), pp. 529–536.

Parkinson, S. et al. (2018) ‘Effect of water depth on muscle activity of dogs when walking on a water treadmill’, Comparative Exercise Physiology. Wageningen Academic Publishers, pp. 1–12.

Preston, T. and Wills, A. P. (2018) ‘A single hydrotherapy session increases range of motion and stride length in Labrador retrievers diagnosed with elbow dysplasia’, The Veterinary Journal. doi:

Williams, S. B. et al. (2008) ‘Functional anatomy and muscle moment arms of the pelvic limb of an elite sprinting athlete: the racing greyhound (Canis familiaris)’, Journal of anatomy. Wiley Online Library, 213(4), pp. 361–372.

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