EQUINE AQUATIC THERAPY

Melissa King, DVM, PhD, DACVSMR (Equine)

Department of Clinical Sciences, Colorado State University, Fort Collins, CO

Key Points:

  • The diverse physical characteristics of aquatic exercise provides unique approaches to individualized rehabilitation for musculoskeletal issues in horses 

  • Water depth will depend on the primary injury, associated functional comorbidities, stage of healing, and established rehabilitation goals. The changes in range of motion will have to be weighed against the benefit of buoyancy at the higher water depths 

Developing successful aquatic therapy protocols first involves reaching an accurate diagnosis, followed by clearly defined rehabilitation goals that consider the biomechanical implications of the original injury. The most effective rehabilitation programs utilize regular, longitudinal patient assessments followed by appropriate adaptation of protocols with both injury-specific and whole-body considerations. These proceedings will provide a brief overview of the key concepts and available evidence in the  field of equine aquatic therapy. Unfortunately, universal recommendations regarding the timing, frequency and specific indications for these interventions are still lacking. As further research is able to define specific parameters, significant advancements within the rehabilitation field can be expected.

  In the rehabilitation setting, the proposed benefits of aquatic exercise include buoyancy, hydrostatic pressure, temperature, and viscosity (resistance) that promote global improvements in muscular timing, range of motion, strength and neuromotor control.1  Several options to employ aquatic therapy for the equine athlete are currently available including above ground underwater treadmills, in-ground underwater treadmills, water walkers and swimming pools (circular or straight). Investigations into the benefits of aquatic therapy for the equine patient have thus far reported subsequent physiologic responses,2-4 biomechanical effects5 and its role in mitigating carpal osteoarthritis.1  Alterations in limb kinematics secondary to varying water depths provides the clinician a means of targeting or sparing flexion/extension joint angles depending on the rehabilitation goals of the specific patient.6 Changes in stride parameters while walking in the underwater treadmill (UWT) at various depths of water demonstrated that water at the level of the ulna results in a longer stride length with a reduced stride frequency, compared to walking with water at the level of the pastern joint.5 Two studies looking specifically at back and pelvic kinematics during aquatic therapy at varying water depths have been performed. When axial rotation, lateral bending and pelvic flexion were evaluated in a population of riding horses, significant increases in rotation and flexion of the back were noted at higher water depths.7  Additionally, pelvic flexion was significantly increased at higher water levels.7 Similarly, increases in cranial thoracic extension and thoracolumbar flexion were appreciated in 14 horses walking in high water compared to water at lower depths.8  Given the resultant spinal and pelvic biomechanical effects of aquatic exercise at varying water depths, the rehabilitation clinician must be mindful that some horses may not tolerate high water levels if pathologic change within the thoracolumbar region results in altered and potentially painful pelvic range of motion. Similar considerations should be given to horses with spinous impingement within the cranial thoracic region as high water depths may exacerbate inappropriate spinal extension.8

Aquatic therapy for the management of carpal osteoarthritis has demonstrated enhanced static postural control under varying stance conditions, along with restored carpal passive range of motion, evenly distributed thoracic limb axial loading, symmetrical timing of select thoracic limb musculature and decreased synovial membrane inflammation. Results from this study indicate that underwater treadmill exercise is a viable therapeutic option in managing OA in horses, which is fundamental to providing evidence-based support for equine aquatic treatment.1,9

Swim training and equine underwater treadmill protocols were initially developed for the primary purpose of rehabilitation for musculoskeletal injuries. However, they are also commonly used for conditioning and to maintain fitness in equine athletes. While previous studies in humans demonstrate that exercising on a water treadmill achieves analogous physiologic responses and cardiorespiratory fitness as dry treadmill training, similar results are lacking in the horse. Although underwater treadmill exercise is considered a form of resistance training studies exploring changes in heart rate, blood lactate and muscle metabolic properties have not been able to demonstrate a significant training effect.10 More recent studies measuring peak oxygen consumption in horses undergoing underwater treadmill training compared to dry treadmill training demonstrated increases in VO2 max in those horses exercising in the underwater treadmill at stifle water height. The higher peak VO2  consumption indicates those horses exercising in the underwater treadmill at higher water depths have a greater aerobic capacity and thus improved conditioning.11 Unlike underwater treadmill exercise, swim training programs have demonstrated improvements in cardiovascular function, reductions in musculoskeletal injury (e.g., tendonitis) and increases in fast-twitch, high-oxidative muscle fibers, which reflect improved aerobic capacity.12,13  Fine-wire electromyography has also been used to measure increases in muscle activation of the thoracic limb musculature during pool swimming exercise, compared to overground walking.14  However, caution should be applied when swimming horses with respiratory compromise as the hydrostatic pressure of water limits adequate ventilation.  During swimming exercise horses have an increase in respiratory rate (30 breaths/min), increases in both inspiratory and expiratory pressures, and a prolonged expiratory time.15  The delay in expiration is a compensatory mechanism utilized by the horse to assist in maintaining buoyancy by minimizing the sudden collapse of lung volume. In addition, horses are not natural swimmers and often use their thoracic limbs to maintain balance while the pelvic limbs are primarily used for propulsion.  The explosive nature of the pelvic limb propulsion often results in extreme ranges of motion through the hip, stifle, and hock joints.  Moreover, upon entry into the water horses often adopt a posture that results in cervical, thoracolumbar and pelvic extension, and as a result horses with thoracolumbar, sacroiliac, hip, stifle, or hock injuries should be approached with caution. 

The diverse physical characteristics of aquatic therapies provide unique approaches to individualized rehabilitation of musculoskeletal issues in horses.  Well-designed, controlled, clinical trials using aquatic exercise are needed in horses to determine dosages effects (e.g., water level, duration, and speed) and to assess clinical changes in soft tissue swelling, joint stability and motor control patterns associated with adaptive and maladaptive compensatory gait alterations. 

 

References:

1.     King M, Haussler K, Kawcak C, et al. Effect of under-water treadmill exercise on postural sway in horses with experimentally induced carpal osteoarthritis. Am J Vet Res 2013;74:971-982.

2.     Hobo S, Yosjida K, Yoshihara T. Characteristics of respiratory function during swimming exercise in Thoroughbreds. J V Med Sci 1998;60(6):687-689.

3.     Voss B, Mohr E, Krzywanek H. Effects of aqua-treadmill exercise on selected blood parameters and on heart-rate variability of horses. J Vet Med Assoc Physiol Pathol Clin Med 2002;49(3)137-143.

4.     Nankervis KJ, Williams RJ. Heart rate responses during acclimation of horses to water treadmill exercise. Equine Vet J 2006;36(Suppl):110-112.

5.     Scott R, Nankervis K, Stringer C, et al. The effect of water height on stride frequency, stride length and heart rate during water treadmill exercise. Equine Vet J 2010;38(Suppl):662-664.

6.     Mendez-Angulo JL, Firshman AM, Groschen DM, et al. Effect of water depth on amount of flexion and extension of joints of the distal aspects of the limbs in healthy horses walking on an underwater treadmill. Am J Vet Res 2013;74(4):557-566.

7.     Mooij MJW, Jans W, den Heijer GJL, et al. Biomechanical responses of the back of riding horses to water treadmill exercise. The Vet J 2013;198:120-123.

8.     Nankervis KJ, Finney P, Launder L. Water depth modifies back kinematics of horses during water treadmill exercise. Equine Vet J 2016;48:732-736.

9.     King M, Haussler KK, Kawcak CE, et al.  Biomechanical and physiologic responses to underwater treadmill exercise in horses with experimentally-induced carpal osteoarthritis. Am J Vet Res 2017;78(5):558-569.

10.  Firschman AM, Borgia LA, Valberg SJ. Effects of training at a walk on conventional and underwater treadmills on fiber properties and metabolic responses of superficial digital flexor and gluteal muscles to high-speed exercise in horses. Am J Vet Res 2015; 76: 1058-1065.

11.  Persephone G, Bond S, Sides R. Workload of horses on a water treadmill: effect of speed and water height on oxygen consumption and cardiorespiratory parameters. BMC Vet Res 2017; 13(360): 1-9.

12.  Misumi K, Sakamoto H, Shimizu R. Changes in skeletal muscle composition in response to swimming training for young horses. J Vet Med Sci 1995;57:959-961.

13.  Misumi K, Sakamoto H, Shimizu R. The validity of swimming training for two-year-old thoroughbreds. J Vet Med Sci 1994;56:217-222.

14.  Tokuriki M, Ohtsuki R, Kai M, et al. EMG activity of the muscles of the neck and forelimbs during different forms of locomotion. Equine Vet J Suppl 1999;30:231-234.

15.  Hobo S, Yosjida K, Yoshihara T. Characteristics of respiratory function during swimming exercise in Thoroughbreds. J Vet Med Sci 1998;60:687-689.