The purpose of this study was to investigate, theoretically, to what extent muscle properties could contribute to recovery from perturbations during locomotion. Four models with different actuator properties were created: the FLVT model, which encompassed force-length (FL) and force-velocity (FV) characteristics of human muscles as well as muscle stimulation inputs as functions of time (T); the FLT model, which had muscles without force-velocity characteristics; the FVT model, which had muscles without specific force-length characteristics; and the MT model, which had no muscles but was driven by joint moments (M) as a function of time. Each model was exposed to static and dynamic perturbations and its response was examined. FLVT showed good resistance to both static and dynamic perturbations. FLT was resistant to static perturbation but could not counteract dynamic perturbation, whereas the opposite was found for FVT. MT could not counteract either of the perturbations. Based on the results of the simulations, skeletal muscle force-length-velocity properties, although interactively complex, contribute substantially to the dynamic stability of the musculoskeletal system.

A kinematic study was performed on a group of 8 Standardbred stallions. Recordings were done using a modified CODA-3 optoelectronic kinematic analysis system with the horses running on a treadmill at speeds of 6, 7, 8, or 9 m/s. Linear and temporal gait characteristics, joint angle diagrams and the trajectories of the hoof in a plane perpendicular to the direction of movement were studied. Two consecutive recording sessions were held at an age of 21–23 months, and a third was held 5 months later after an intensive training period. Joint angle diagrams appeared to show a similar pattern for all horses though certain individual characteristics could be identified. Only a few kinematic parameters appeared to have significantly changed after the 5-month training period (p < 0.05). The hoof trajectories showed marked and consistent differences between front and hind hooves, but the most striking feature was the very individual character of the patterns exhibited, leading to the assumption that these patterns could possibly be used as the ‘fingerprint’ of the horse.

No abstract

Summary Skin displacement was investigated at 16 sites in the front and hind limbs of four Dutch Warmblood horses at the trot. For visualisation of the bone under the skin, a measuring device mounted on a Steinmann pin driven into the bone under investigation, was employed. Mean displacements ranged from 8 mm (X‐displacements proximal and distal metacarpus) to 142 mm (Y‐displacement caudal part of greater trochanter). When compared with previously determined skin displacement patterns at walk, mean displacements at trot were of the same magnitude whereas the shape of the time‐displacement curve was different. The latter may be attributed to differences in relative duration of stance and swing phases between the walk and the trot.

The in vivo strains of the musculus interosseus medius (suspensory ligament) and its rami extensorii (extensor branches) in the forelimb of the horse were determined from angular changes of the metacarpophalangeal and the distal interphalangeal joints. For this purpose, regression models were fitted to strains and joint angle combinations measured in in vitro limb loading experiments. The in vivo strains were computed from the kinematics of 8 horses at the walk, the trot and the canter. It was found that the extensor branches were strained about 1.0% at hoof impact, which indicates that they passively extend the interphalangeal joints just prior to impact and prevent flexion of the pastern joint just thereafter. The maximal strain of the suspensory ligament amounted to 3.4% at the walk, 5.6% at the trot and 6.3% at a slow canter.