Underwater Treadmills Rapidly Build Back Muscles in Horses

Underwater treadmills are popular tools for training purposes and for rehabilitating horses following injury. Results of underwater treadmills vary based on the incline, treadmill speed, and depth of water. One study showed that recurrent incline underwater treadmill exercise develops muscles in the back within two weeks of starting this exercise.^*

In the study, six sound, healthy horses habituated to an underwater treadmill underwent six individual 15-minute sessions for four weeks (24 sessions total). The water height was halfway between knee and fetlock, the treadmill speed was an average of 3.6 km/hour (0.62 miles/hour), and the treadmill incline was 4%.

Tracings of the back muscles (called the epaxial muscles, which includes the longissimus dorsi) were obtained at the start of the study and then at one-week intervals for the duration of the study. Those tracings were obtained using a saddle fitting kit with a flexible curved ruler that molds to the surface of the back. The ruler was then placed on graph paper and the shape of the musculature sketched, with the change in the shape of the ruler measured throughout the four-week study. Measurements were made at four levels: the fifth, ninth, fourteenth, and eighteenth thoracic vertebrae (T5, T9, T14, and T18).

“A significant, progressive increase in the epaxial muscle profiles started at the second week and continued for the duration of the four-week study,” explained Kathleen Crandell, Ph.D., a Kentucky Equine Research nutritionist.

The most significant increases in epaxial muscle profiles were observed at T5 and T18, although increases were noted at all four levels.

“These results support the researchers’ hypothesis that underwater treadmill therapy helps develop epaxial muscles. They also support the theory that rehabilitation using a treadmill activates and builds the paraspinal musculature in the thoracic region of the spine,” said Crandell.

These results concur with previously published data that found water treadmill exercise increases thoracic epaxial muscle development after 20 weeks of exercise. The current study, however, showed much earlier improvement. Compared to the previous study that did not use an incline, the current study used a 4% incline, which might have contributed to the faster increase in epaxial musculature.

“Both water level and incline can influence epaxial muscle activation and growth and there could be a synergistic effect between those two variables,” advised Crandell.

Additional studies using various inclines, water levels, and speeds would be beneficial, in addition to using ultrasound to measure cross-sectional area of the epaxial muscles rather than simply tracing the topline.

“Strengthening the epaxial muscles with an inclined underwater treadmill can allow the thoracic muscles to freely engage with a greater amount of flexion over the lumbar region without the negative impact on back posture from added weight of a rider or saddle. Further, it allows for more symmetrical muscle development by recruiting the vertebral-stabilizing muscles, which in turn have a cumulative effect on muscle growth,” Crandell said.

Nutrition also plays an important role in muscle growth. High-quality protein with the right balance of amino acids is important for building and maintaining muscle integrity. In particular, the branched-chain amino acids leucine, isoleucine, and valine may stimulate protein synthesis and delay onset of fatigue.

^*Fair, N., S. Blake, and R. Blake. 2023. Four weeks of incline water treadmill exercise can contribute to increase epaxial muscle profile in horses. Veterinary Medicine International:9090406.