Change in muscle development of horses undergoing 20 weeks of water treadmill exercise compared with control horses

Objectives: To describe changes in MD over a 20‐week period in sports horses that use WT in their regular training regime and in control horses. Study design: Observational study. Methods: Forty‐four horses (age: 11 ± 4 years) that use the WT weekly/fortnightly and 23 horses (age: 11 ± 4 years) that do not use WT were recruited, paired by breed and stage of training. All horses were deemed clinically sound. Subjective MD assessment of specific regions was undertaken using a previously published grading scale at weeks 0 and 20, including neck, cervical trapezius, thoracic trapezius, thoracic, lumbosacral, gluteal, hamstring, hindlimb adductor/abductor, abdominal musculature. MD assessments were carried out by an experienced veterinarian and a trained research assistant; inter and intra‐observer repeatability was confirmed. Data from weeks 0 and 20 were compared using a Wilcoxon‐Signed Ranks test, with a significance level P < .05. Results: After 20 weeks of WT, MD significantly increased at all locations (P ≤ .046) except the cervical trapezius and the abdominal region, with the most significant increase in the gluteal and hindlimb musculature (P < .0001). In the control horses, after 20 weeks MD only significantly increased in the hamstring musculature (P = .007). Main limitations: Slightly higher proportion of dressage horses in the control group (75% vs 60%). Conclusions: It appears regular WT exercise increases MD, particularly for musculature used to create movement patterns seen on the WT, increasing tarsal flexion. Less increased cervical trapezius/abdominal MD indicates WT exercise may be more beneficial for development hindlimb/lumbosacral musculature than elevation of the thorax, supporting clinical impression. WTs may be appropriate to be used under veterinary guidance as part of a directed rehabilitation/training programme to increase core and hindlimb muscle development.