SummaryReasons for performing study: Water treadmill exercise is often incorporated into rehabilitation programmes for horses yet little is known about the biomechanical and physiological responses to water walking. Objectives: To establish whether stride frequency (SF) reached steady state as a result of 6 introductory water treadmill sessions and then to investigate the effect of increasing water height on SF, stride length (SL) and heart rate (HR).

Muscle function depends in part on the interplay between its activity and its length within the stretch-shortening cycle. The longissimus dorsi is a large epaxial muscle running along the thoracic and lumbar regions of the equine back. Due to its anatomical positioning, the longissimus dorsi has the capability of contributing to many functions: developing bending moments in the dorsoventral and lateral (coupled to axial rotation) directions and also providing stiffness to limit motion in these directions. We hypothesize that the exact function of the longissimus dorsi will vary along the back and between gaits as the relation between activity and motion of the back changes. Electromyograms (EMG) were recorded at walk (inclined and level) and trot (on the level) on a treadmill from the longissimus dorsi at muscle segments T14, T16, T18 and L2. Back motion was additionally measured using a fibre-optic goniometer. Co-contractions of the muscle between its left and right sides were quantified using correlation analysis. A greater dominance of unilateral activity was found at more cranial segments and for level walking, suggesting a greater role of the longissimus dorsi in developing lateral bending moments. Timing of the EMG varied between muscle segments relative to the gait cycle, the locomotor condition tested and the flexion–extension cycle of the back. This supports the hypothesis that the function of the longissimus dorsi changes along the back and between gaits.

The purpose of this study was to determine whether significant differences exist in the position of a horse rider when assessed at different points in the horse's stride cycle at walk, trot and canter on the right rein. Video analysis was used to determine the absolute angles of the trunk, thigh and lower leg of five subjects during the walk, rising trot and canter. The range of movement of the trunk, thigh and lower leg during each gait was also determined. At walk significant differences in the rider's trunk angle were found between limb impacts (P<0.05). At trot significant differences were found in all angles between impacts of the horse's diagonal limb pairs (P<0.05). At canter, there were no significant differences in rider position between limb impacts. The range of movement of the trunk was 5.9°, 4.1° and 4.7° for walk, trot and canter, respectively. The corresponding ranges of the thigh and lower leg were 1.9°, 7.3° and 4.4°, and 2.9°, 5.2° and 3.9°, respectively. This preliminary study has demonstrated differences in rider posture between limb impacts in walk and trot. Further work is necessary to investigate the forces acting on the rider during each gait and the postural strategies employed by riders to maintain a balanced position. Such work is a necessary forerunner to the study of rider influence on horse performance.

Pain, atrophy and dysfunction of the longissimus dorsi in the equine back can lead to poor performance and altered biomechanics. Back problems are often treated by manipulative therapy to this muscle. The purpose of this study was to identify if manipulative therapy resulted in changes to muscle tone or electromyographic (EMG) activity immediately after treatment. We measured the muscle tone during standing using a mechanical tissue indenter and the EMG activity (both at the T16 level in the longissimus dorsi) during walking around a figure-of-eight course in 26 horses. The horses were randomly assigned into three groups that received: (a) spinal (McTimoney) manipulations, (b) reflex inhibition therapy or (c) a control group that was not manipulated. The muscle tone and activity were measured immediately after treatment. Both the McTimoney and the reflex inhibition groups showed significant decreases in muscle tone (c. 12%) and walking EMG activity (c. 19%). The control group showed no significant change in tone or EMG activity. These results document how the longissimus dorsi muscle responds immediately after manipulative therapy. Further studies would be needed to identify how long such changes persist or if such changes caused a reduction in pain or an increase in performance.

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SummaryReasons 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 (À3.0°) than control (0.1°, P = 0.001) and L3 AMPmax significantly greater in high water (À1.9°) than control (À4.8°, 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.

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Previous experience of water treadmill exercise should be taken into consideration prior to collecting physiological and biomechanical data. Further studies detailing the physiological and biomechanical responses are required prior to making recommendations for the incorporation of this mode of exercise into rehabilitation programmes.