Water depth modifies back kinematics of horses during water treadmill exercise

Reasons for performing study Water treadmill exercise can be incorporated into the rehabilitation programmes of horses recovering from back pathology, yet little is known about the effect of this type of exercise on thoracolumbar movement ranges. Objectives To measure the flexion-extension range of motion (FE ROM) of the thoracolumbar spine and pelvic vertical displacement during water treadmill walking at 3 water depths and compare these with the control condition. Study design Within-subject trial using a crossover design in healthy horses. Methods A total of 14 horses walked at 0.8 m/s on a water treadmill for 3 min at each of the following depths; hoof (control), metatarsophalangeal joint (low), tarsal joint (medium) and femoropatellar joint (high). Skin surface markers on T6, T10, T13, T18, L3, L5 and S3 were used to obtain FE ROM and the minimum and maximum angular motion pattern values (AMPmin and AMPmax) for T10, T13, T18, L3 and L5. Markers placed on left and right tuber coxae were used to obtain pelvic vertical displacement. Friedman's tests and post hoc Wilcoxon's signed ranks tests were used to determine the effects of water depth on measured variables. Results The FE ROM of T10 (8.4°), T13 (8.1°), T18 (6.9°) and L3 (6.4°) when walking at high depth was significantly greater than control (5.5, 5.7, 5.1 and 5.1°, respectively; P<0.008); T13 AMPmin was significantly lower in high water (−3.0°) than control (0.1°, P = 0.001) and L3 AMPmax significantly greater in high water (−1.9°) than control (−4.8°, P = 0.001). There was no significant association between pelvic vertical displacement and water depth. Conclusions Walking in high water causes cranial thoracic extension and thoracolumbar flexion when compared with walking in water at hoof depth. This postural change should be considered when designing rehabilitation programmes for horses with back and/or hindlimb pathology