Summary 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. 268 EQUINE VETERINARY JOURNAL Equine vet. J. (2009) 41 (3) 268-273 doi: 10.2746/042516409X397389 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 N. M. WALDERN*, T. WIESTNER, K. VON PEINEN, C. G. GÓMEZ ÁLVAREZ † , L. ROEPSTORFF ‡ , C. JOHNSTON ‡ , H. MEYER § and M. A. WEISHAUPT Equine Department, Vetsuisse Faculty, University of Zurich, CH-8057 Zurich, Switzerland; † Department of Equine Sciences, Utrecht University, Utrecht, The Netherlands and Equine Division, Veterinary Medicine, Católica de Temuco University, Chile; ‡ Department of Veterinary Anatomy and Physiology, Swedish University of Agricultural Sciences, 75007 Uppsala, Sweden; and § Am Wisselsbach 22, 52146 Würselen, Germany. Keywords: horse; dressage; GRF; head-neck position; treadmill Introduction The most suitable posture in which to ride a horse has been subject of much discussion since the beginning of equestrian sports. Criteria for choice of a certain posture include its effect on horses’ health, its influence on athletic capability, the ease with which it can be achieved by the rider and, to a lesser extent, the aesthetic appearance. As only an optimal weight distribution between fore- and hindlimbs allows the development of regularity and expressiveness, a well balanced horse is essential for the achievement of more advanced movements in dressage or jumping, but also to prevent wear-and-tear on the locomotor apparatus. According to riding manuals, the position of the horse’s head is thought to have an important influence not only on forelimb- hindlimb balance, but also on the movement of fore- and hindlimbs and the back. Amongst riders, lowering the neck and working the horse forward downward is often claimed to increase the movement of the back and to strengthen the muscles of the ventral abdomen and the back (Denoix and Pailloux 1996; Karl 1999). High positioning of the head-neck segment should increase the amplitude of forelimb range of motion (de Carpentry 1972) as well as hindlimb engagement (Licart 1951). Also from the scientific point of view, given the well confirmed theory of the ‘bow-and-string’ principle (Slijper 1946; Denoix 1999), extensive effects on the locomotion system including the back are to be expected when the head-neck position (HNP) is varied. Kinematic analysis of the back in unridden horses revealed a significant influence of the HNP on back kinematics (Gómez Álvarez et al. 2006). In one study evaluating 3 different types of reins, it was found that different HNPs mainly affected forelimb kinetics and concluded that the reins’ chief effect might be the training of the neck muscles (Biau et al. 2002). Force plate analysis showed that with the application of draw reins combined with normal reins, a shift of weight of the horse caudally could be achieved under the rider (Roepstorff et al. 2002). In another study using the same experimental set-up and HNPs as in the present study but under the rider, it was found that an extremely elevated *Author to whom correspondence should be addressed. [Paper received for publication 11.06.08; Accepted 18.11.08]