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The amount of protraction-retraction of the limbs during water treadmill (WT) walking has implications for postural and muscular development of horses undertaking this exercise for training and rehabilitation purposes. The objective of this study was to compare protraction-retraction of both forelimbs (FLs) and hind limbs (HLs) during dry treadmill (DT) and WT exercise at the typical walking speed of each as used in practice. Inertial motion sensors attached to the metacarpal/metatarsal bones were used to compare maximal protraction (PROMAX), retraction (RETMAX), and total protraction-retraction range of movement (ROM) across five walking conditions: DT at 1.6 m/s; and WT at 0.8 m/s at four water depths, hoof depth (WTHOOF), fetlock depth (WTFET), hock depth (WTHOCK), and stifle depth (WTSTIFLE). Forelimb ROM was lowest at WTSTIFLE and significantly lower than DT (P < .001). Hind limb ROM was highest at WTSTIFLE and significantly greater than DT (P < .001). Forelimb PROMAX was significantly lower at WTHOCK (P = .001) and WTSTIFLE (P < .001) than DT. Hind limb RETMAX was higher at WTHOCK (P = .001) than on DT and was significantly greater at WTSTIFLE and WTHOCK than WTFET (P < .001 and P = .001, respectively). Walking slowly (0.8 m/s) on a WT reduces FL protraction-retraction ROM and increases HL protraction-retraction ROM when compared with walking at normal speed (1.6 m/s) on a DT. The potential for FL protraction to be decreased and HL retraction to be increased should be taken into account when designing training and rehabilitation programs using this exercise modality.Drag experienced during water treadmill walking limits forelimb protraction in horses.As water depth is increased, the range of movement of the forelimb is reduced.As water depth is increased, the range of movement of the hind limb is increased.As drag increases with water depth, protraction of the forelimb, but not the hind limb is reduced.