No abstract

BW, body size, and relative dog velocity must be accounted for when wanting to obtain GRF variables that are comparable between different dogs.

Summary Reasons for performing study: The compensatory mechanisms of horses with weightbearing hindlimb lameness are still not fully understood. Hypothesis: That weightbearing, unilateral hindlimb lameness would not only alter stride characteristics to diminish structural stress in the affected limb but also induce compensatory load adjustments in the other supporting limbs. Objective: To document the load and time shifting mechanisms of horses with unilateral weightbearing hindlimb lameness. Methods: Reversible lameness was induced in 8 clinically sound horses by applying a solar pressure model. Three degrees of lameness (subtle, mild and moderate) were induced and compared with the nonlame (sound) control measurement. Vertical ground reaction forces were recorded for all 4 limbs simultaneously on an instrumented treadmill. Results: Compared to the sound situation, moderate hindlimb hoof lameness induced a decrease in stride duration (‐3.3%) and stride impulse (‐3.1%). Diagonal impulse decreased selectively in the lame diagonal stance (‐7.7%). Within the diagonal limb pair, vertical impulse was shifted to the forelimb during the lame diagonal stance (+6.5%) and to the hindlimb during the sound diagonal stance (+3.2%). Peak vertical force and vertical impulse decreased in the lame limb (‐15%), but only vertical impulse increased in the contralateral hindlimb (+5.7%). Stance duration was prolonged in both hindlimbs (+2.5%). Suspension duration was reduced to a greater extent after push‐off of the lame diagonal limb pair (‐21%) than after the sound diagonal limb pair (‐9.2%). Conclusions: Four compensatory mechanisms could be identified that served to reduce structural stress, i.e. peak vertical force on the affected limb: 1) reduction of the total vertical impulse per stride; 2) diagonal impulse decreased selectively in the lame diagonal; 3) impulse was shifted within the lame diagonal to the forelimb and in the sound diagonal to the hindlimb; and 4) the rate of loading and peak forces were reduced by prolonging the stance duration. Potential relevance: Load shifting mechanisms are not only effective in diminishing peak forces in the affected limb, but also suppress compensatory overload in other limbs. Selected force and time parameters allow the unequivocal identification of the lame limb. Future studies have to examine how far these compensatory mechanisms may be generalised for other defined orthopaedic problems in the hindlimb.

Summary Reasons for performing study: Little is known in quantitative terms about the influence of different head‐neck positions (HNPs) on the loading pattern of the locomotor apparatus. Therefore it is difficult to predict whether a specific riding technique is beneficial for the horse or if it may increase the risk for injury. Objective: To improve the understanding of forelimb‐hindlimb balance and its underlying temporal changes in relation to different head and neck positions. Methods: Vertical ground reaction force and time parameters of each limb were measured in 7 high level dressage horses while being ridden at walk and trot on an instrumented treadmill in 6 predetermined HNPs: HNP1 ‐ free, unrestrained with loose reins; HNP2 ‐ neck raised, bridge of the nose in front of the vertical; HNP3 ‐ neck raised, bridge of the nose behind the vertical; HNP4 ‐ neck lowered and flexed, bridge of the nose considerably behind the vertical; HNP5 ‐ neck extremely elevated and bridge of the nose considerably in front of the vertical; HNP6 ‐ neck and head extended forward and downward. Positions were judged by a qualified dressage judge. HNPs were assessed by comparing the data to a velocity‐matched reference HNP (HNP2). Differences were tested using paired t test or Wilcoxon signed rank test (P<0.05). Results: At the walk, stride duration and overreach distance increased in HNP1, but decreased in HNP3 and HNP5. Stride impulse was shifted to the forehand in HNP1 and HNP6, but shifted to the hindquarters in HNP5. At the trot, stride duration increased in HNP4 and HNP5. Overreach distance was shorter in HNP4. Stride impulse shifted to the hindquarters in HNP5. In HNP1 peak forces decreased in the forelimbs; in HNP5 peak forces increased in fore‐ and hindlimbs. Conclusions: HNP5 had the biggest impact on limb timing and load distribution and behaved inversely to HNP1 and HNP6. Shortening of forelimb stance duration in HNP5 increased peak forces although the percentage of stride impulse carried by the forelimbs decreased. Potential relevance: An extremely high HNP affects functionality much more than an extremely low neck.