An underwater treadmill (also referred to as a ‘water treadmill’) is a common piece of exercise equipment used in equine training and rehabilitation. [1] This type of treadmill is submerged in water so the horse is chest-deep while they are walking. [2]

Working horses in water is increasingly popular as it provides low-impact exercise, encourages horses to move their joints through the full range of motion, and improves muscle building. [1]

Water treadmills are often used in training performance horses as they enable whole body exercise without putting excess strain on the lungs and heart. [1] Many riders use water treadmill exercise as a form of cross-training to improve their horse’s performance. [3]

For horses recovering from injuries, especially those involving joints, tendons, or ligaments, underwater treadmills provide a controlled environment to return to work while minimizing muscle strain.

Benefits of Equine Water Treadmills

Training horses on underwater treadmills provides additional benefits beyond high-speed treadmills (“land treadmills“), providing increased muscle resistance for the horse and greater control over the workout for the trainer.

By submerging the exercising horse in water, physiological effects related to buoyancy, resistance, and water pressure add a unique combination of movement complexity and joint support to the training session. [2]

Buoyancy

When objects are surrounded by water, the water exerts an upward force on them called buoyancy. Objects that float easily have high buoyancy, and objects that sink have low buoyancy.

During a water treadmill session, buoyancy reduces weight bearing on the horse’s hooves, decreasing concussive force on the joints. [2] The measurement of weight on the hooves relative to buoyancy in water is called the functional body weight experienced by the horse.

The overall reduction of concussive force provided by any aquatic activity is why swimming and other underwater exercises are considered low-impact. Conversely, high-impact exercise, such as running on land, puts a great deal of concussive force on the joints.

Water treadmills are popular, especially for horses recovering from joint strain or injury, as low-impact exercise allows for muscle reconditioning without putting vulnerable, healing joints through excessive concussive force. [4]

Practitioners can also adjust water depth within the treadmill enclosure to change the amount of buoyancy placed on the exercising horse. [4] For example, water at the level of the elbow and stifle reduces functional body weight by 10%, while water at the level at the hips reduces functional body weight by about 75%. [4]

Practitioners often start with higher water levels during rehabilitation to maximize buoyancy, then reduce the water level as the horse becomes stronger and better able to bear weight during movement. [4]

Resistance

Water is more dense than air, meaning there is more resistance (drag) when a horse walks in water compared to moving on land. [4]

The faster the horse moves, the more drag is generated, which increases the effort required for the horse to move. [4] Due to this increase in resistance, most horses walk 50% slower than usual on a water treadmill. [4]

Rehabilitation practitioners use this principle to increase workload on the muscles while keeping demand on the respiratory and the cardiovascular systems (lungs and heart) low. [4] This helps build strength in the musculoskeletal system without intense cardiovascular exercise. [4]

Water Pressure

The weight of water itself puts force on objects submerged in it. This force is referred to as water pressure, which may benefit some types of injuries. [4] When a horse walks on a water treadmill, water in the enclosure puts compression force on the limbs and any other parts of the body submerged in it.

Increased pressure promotes fluid drainage within the limb, resulting in reduced swelling of inflamed tissues. [2] Decreasing swelling improves joint range of motion and temporarily reduces pain associated with movement of the joint. [2]

Increased pressure can also re-activate nerves associated with normal joint movement. [2] Joints sometimes trigger inhibition (reduced function) of their associated muscles as a protective response to injury. [2] Nervous inhibition of joint function prevents further injury, but needs to be reversed during rehabilitation to regain full range of motion. [2]

Using water pressure to reactivate pain-inhibited muscle groups can also lead to improved postural stability. [5] One study of horses with knee arthritis showed water treadmill exercise improved the horses’ balance and muscle control when on land. [5]

These improvements led to decreased lameness scores during gait analysis, likely due to overall better conformation during motion in water treadmill training. [5]

Research in human medicine shows water pressure can reduce activation of inhibitory nerve endings while also stimulating nerve endings responsible for muscle activation and tone. [2] This process may restore normal muscle function surrounding the joint, which helps reverse and prevent muscle wasting associated with an injured joint. [2]

Uses

Veterinarians, rehabilitation practitioners, and trainers commonly use water treadmills for conditioning high performance horses and as part of injury recovery treatment protocols. [1][3]

Most practitioners recommend using water treadmill exercise a maximum of 1-2 times a week for conditioning purposes. [1] Practitioners can adjust the speed, water depth, and duration of exercise to challenge the horse without causing muscle fatigue or strain. [1]

There is minimal research available to define protocols for equine water treadmill use in injury rehabilitation, so the frequency, speed, water depth, and duration of exercise depends on the practitioner and their evaluation of the horse. [1]

Conditions that may benefit from water treadmill exercise during rehabilitation include: [3][4]

Preparation

It’s crucial to prepare adequately before starting equine water treadmill training to minimize the risk of injury to horses and handlers. [1]

Safety procedures for handlers should be designed and reviewed regularly for each specific water treadmill enclosure. [1] Handlers should also wear protective equipment such as helmets, gloves, and closed-toe shoes when working with a horse in the treadmill enclosure. [1]

General preparation of the horse for a water treadmill session includes: [1]

  • Ensuring the horse has no wounds or scrapes on the skin
  • Checking the horse’s shoes to ensure they are secure
  • Brushing or washing the horse’s legs and picking out the feet
  • Wrapping the tail

These steps reduce the risk of injury and minimize contamination of the water. [4]

Habituation

All horses require a habituation period of around 3-4 sessions to become accustomed to the water treadmill. [1] Most horses habituate quickly to water treadmills with an appropriate, slow introduction. [4]

Current recommendations for habituation are three sessions of 15 minutes on three consecutive days, with a slow increase in water depth with each day. [1] The sessions should not be rushed, and the horse should be given adequate time to adjust to the sights, scents, and sounds associated with the water treadmill. [1]

Some horses may benefit from light sedation prior to their first water treadmill session to help them adjust in a calm manner. [1]

Ideally, by the end of the first habituation session, the horse should be comfortable walking comfortably consistently for 10-15 minute in fetlock-deep water. [1]

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Water Treadmill Workout Design

Practitioners can adjust the speed, water depth, and the length of an exercise session to achieve a desired effect.

Speed

Unlike training on a land treadmill, water treadmills are not primarily used for high-speed cardio training. Most practitioners only walk horses in a water treadmill due to the increased effort movement requires. [1]

Additionally, it is widely believed that benefits of water treadmill use are achievable at the walk, without requiring trotting. [1] A survey of water treadmill practitioners in the United Kingdom showed that only one in 10 practitioners routinely exercised horses in trot on a water treadmill. [1]

Water Depth

Increasing the depth of the water increases the horse’s workload significantly. [1] One study shows water depth impacts oxygen consumption and heart rate more than the speed of the treadmill. [6]

Many practitioners use water depth to increase the difficulty of water treadmill exercise rather than increasing speed. [1] Practitioners commonly use deep water, up to the levels of the hocks, during training sessions. [3]

Practitioners can also use water depth to target specific rehabilitation goals in horses with injuries. [1] During rehabilitation, practitioners commonly use water levels just above the injured structure to work muscles in the specific treatment area. [3]

Duration of Exercise

Although water treadmill exercise is less strenuous on the cardiovascular and respiratory systems, training sessions can lead to muscle fatigue and strain. [1] Practitioners monitor horses during their exercise sessions to ensure they are not showing signs of muscle fatigue that result in further injury. [1]

Signs of muscle fatigue include: [1]

  • Horse leaning against one side of the treadmill
  • Horse moving between the front and back of the treadmill rather than staying in the middle
  • Excessive movement of the head
  • Irregular rhythm to the horse’s steps

If a horse shows signs of muscle fatigue, they should not continue exercising on the water treadmill, and the speed and water depth should be re-evaluated prior to the next session. [1]

A survey of practitioners showed equine water treadmill sessions range from 5 to 54 minutes. [1] In general, practitioners use longer sessions for training purposes and shorter sessions during rehabilitation programs. [3]

Supporting Evidence

Most of the scientific research regarding equine water treadmills focuses on their use in performance conditioning, rather than rehabilitation.

Effects on Posture and Gaits

The combined effect of buoyancy and drag forces horses to adopt a different gait and posture from how they move over land. [4]

As the depth of the water increases, horses increase flexion of the lower limb joints and lower back, which can be used for a therapeutic effect. [4] Studies show that water at hock level increases range of motion in the knee, while water at the stifle level increases range of motion in the hocks. [7]

Increasing water depth also increases stride length resulting in the horse taking fewer, slower steps. [8] Some researchers suggest that the gait produced by water treadmills may increase performance of dressage horses, as slow, long strides are desirable in this discipline. [8]

Additionally, increased drag from water may promote hindlimb muscle development, which is desirable in sport horses requiring collected movements, like dressage and reining. [4]

Studies show water treadmill exercise may promote a flexed posture of the back, which may benefit conditions such as overriding dorsal spinous processes (“kissing spine“). [8]

When using water treadmills for spinal rehabilitation, it’s important for the water level to be at the location of the treatment area (i.e. the horse is submerged up to the neck).

Studies show that increasing water depth increases extension (hollowing of the back) towards the shoulders, while causing flexion (rounding of the back) towards the pelvis. [7]

If these opposing forces are not well managed by the practitioner, they can lead to further strain or injury.

Exercise Intensity

The intensity of water treadmill exercise is considered low, and likely has a similar effect to exercise over raised poles. [4] Therefore, water treadmill use may be a suitable replacement for other low-intensity exercises such as ground schooling.

Several studies show water treadmill exercise does not significantly increase the horse’s heart rate compared to walking over the ground. [4][8] Currently, studies show the maximum heart rate of horses on water treadmills is around 140 beat per minute, compared with 160 beats per minute or more during galloping or swimming. [8]

Long-term studies over 4 and 8-week periods showed no increase in cardiovascular performance measures as a result of water treadmill training. [8]

One study showed that racehorses exercised in a water treadmill program for 18 days had a 16% higher oxygen intake capacity compared to horses that did not receive water treadmill conditioning. [9] This finding suggests water treadmill exercise may improve endurance and oxygen capacity in horses, while keeping cardiac effort low. [9]

Rehabilitation

There are few studies on the efficacy of water treadmills in rehabilitating equine lameness disorders. One study showed water treadmill exercise can improve postural stability in horses with arthritis of the knee, which may promote balance and joint stability. [5]

In dogs, studies show that water treadmill exercise can increase joint range of motion, build muscle mass, and improve recovery rates. [8] However, many of these studies use a combination of rehabilitation therapies, so the effects of water treadmill exercise itself is unclear. [8]

Aquatic exercise has been shown to improve muscular timing and control in humans, which may be relevant to rehabilitating horses with neurologic disease (disease affecting the nervous system). [10]

While there are currently no studies on water treadmill efficacy in cases of equine neurologic disease, anecdotal reports suggest there may be some value in this modality.

One proposed approach of using water treadmill exercise in neurologic cases is to progressively increase duration of the sessions and change the depth of the water frequently to improve muscle control. [10]

Side Effects

Water treadmill use as part of a conditioning program or for maintaining performance is safe for healthy horses. [1] There are few reported side effects of using water treadmills. [3] Always consult with a qualified expert before introducing new training and conditioning programs to your horse’s regimen.

There are some cases when water treadmill therapy is not advised, such as horses with: [1][2]

Summary

Water treadmills are a common component of rehabilitation and conditioning programs for horses.

  • Water treadmill exercise may benefit arthritis, ligament and tendon injuries, and kissing spine
  • Adjusting the speed of the treadmill, water depth, and duration can optimize the exercise session for specific outcomes
  • Water treadmill use is safe for healthy horses under the guidance of trained professionals

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References

  1. Nankervis, K. et al. Consensus for the General Use of Equine Water Treadmills for Healthy Horses. Animals. 2021. doi: 10.3390/ani11020305. View Summary
  2. King, M. R. Principles and Application of Hydrotherapy for Equine Athletes. Veterinary Clinics of North America: Equine Practice. 2016. doi: 10.1016/j.cveq.2015.12.008. View Summary
  3. Tranquille, C. A. et al. International Survey of Equine Water Treadmills—Why, When, and How?. Journal of Equine Veterinary Science. 2018. doi: 10.1016/j.jevs.2018.05.220.
  4. Nankervis, K. J. et al. The Use of Treadmills Within the Rehabilitation of Horses. Journal of Equine Veterinary Science. 2017. doi: 10.1016/j.jevs.2017.01.010.
  5. King, M. R. et al. Effect of Underwater Treadmill Exercise on Postural Sway in Horses with Experimentally Induced Carpal Joint Osteoarthritis. ajvr. 2013. doi: 10.2460/ajvr.74.7.971. View Summary
  6. Greco-Otto, P. et al. Workload of Horses on a Water Treadmill: Effect of Speed and Water Height on Oxygen Consumption and Cardiorespiratory Parameters. BMC Vet Res. 2017. doi: 10.1186/s12917-017-1290-2. View Summary
  7. Tranquille, C. et al. Effect of Water Depth on Limb and Back Kinematics in Horses Walking on a Water Treadmill. Journal of Equine Veterinary Science. 2022. doi: 10.1016/j.jevs.2022.104025. View Summary
  8. Tranquille, C. A. et al. Current Knowledge of Equine Water Treadmill Exercise: What Can We Learn From Human and Canine Studies?. Journal of Equine Veterinary Science. 2017. doi: 10.1016/j.jevs.2016.10.011.
  9. Greco-Otto, P. et al. Conditioning Equine Athletes on Water Treadmills Significantly Improves Peak Oxygen Consumption. Veterinary Record. 2020. doi: 10.1136/vr.104684. View Summary
  10. Johnson, S. A. Rehabilitation Strategies for the Neurologic Horse. Veterinary Clinics of North America: Equine Practice. 2022. doi: 10.1016/j.cveq.2022.05.007. View Summary