Influence of different head-neck positions on vertical ground reaction forces, linear and time parameters in the unridden horse walking and trotting on a treadmill.

REASONS FOR PERFORMING STUDY: It is believed that the head-neck position (HNP) has specific effects on the loading pattern of the equine locomotor system, but very few quantitative data are available. OBJECTIVE: To quantify the effects of 6 different HNPs on forelimb-hindlimb loading and underlying temporal changes. METHODS: Vertical ground reaction forces of each limb and interlimb coordination were measured in 7 high level dressage horses walking and trotting on an instrumented treadmill in 6 predetermined HNPs: HNP1--unrestrained; HNP2--elevated neck, bridge of the nose in front of the vertical; HNP3--elevated neck, bridge of the nose behind the vertical; HNP4--low and flexed neck; HNP5--head and neck in extreme high position; and HNP6--forward downward extension of head and neck. HNP1 served as a velocity-matched control. RESULTS: At the walk, the percentage of vertical stride impulse carried by the forehand (Iz(fore)) as well as stride length and overreach distance were decreased in HNP2, HNP3, HNP4 and HNP5 when compared to HNP1. At the trot, Iz(fore) was decreased in HNP2, HNP3, HNP4 and HNP5. Peak forces in the forelimbs increased in HNP5 and decreased in HNP6. Stance duration in the forelimbs was decreased in HNP2 and HNP5. Suspension duration was increased in HNP2, HNP3 and HNP5. Overreach distance was shorter in HNP4 and longer in HNP6. CONCLUSIONS: In comparison to HNP1 and HNP6, HNPs with elevation of the neck with either flexion or extension at the poll as well as a low and flexed head and neck lead to a weight shift from the forehand to the hindquarters. HNP5 had the biggest effect on limb timing and load distribution. At the trot, shortening of forelimb stance duration in HNP5 increased peak vertical forces although Iz(fore) decreased. POTENTIAL RELEVANCE: Presented results contribute to the understanding of the value of certain HNPs in horse training