During trot, the rider can either rise from the saddle during every stride or remain seated. Rising trot is used frequently because it is widely assumed that it decreases the loading of the equine back. This has, however, not been demonstrated in an objective study.To determine the effects of rising and sitting trot on the movements of the horse.Sitting trot has more extending effect on the horse's back than rising trot and also results in a higher head and neck position.Twelve horses and one rider were used. Kinematic data were captured at trot during over ground locomotion under 3 conditions: unloaded, rising trot and sitting trot. Back movements were calculated using a previously described method with a correction for trunk position. Head-neck position was xpressed as extension and flexion of C1, C3 and C6, and vertical displacement of C1 and the bit.Sitting trot had an overall extending effect on the back of horses when compared to the unloaded situation. In rising trot: the maximal flexion of the back was similar to the unloaded situation, while the maximal extension was similar to sitting trot; lateral bending of the back was larger than during the unloaded situation and sitting trot; and the horses held their heads lower than in the other conditions. The angle of C6 was more flexed in rising than in sitting trot.The back movement during rising trot showed characteristics of both sitting trot and the unloaded condition. As the same maximal extension of the back is reached during rising and sitting trot, there is no reason to believe that rising trot was less challenging for the back.
The simplest model possible for bouncing systems consists of a point mass bouncing passively on a mass-less spring without viscous losses. This type of spring-mass model has been used to describe the stance period of symmetric running gaits. In this study, we investigated the interaction between horse and rider at trot using three models of force-driven spring (-damper)-mass systems. The first system consisted of a spring and a mass representing the horse that interact with another spring and mass representing the rider. In the second spring-damper-mass model, dampers, a free-fall and a forcing function for the rider were incorporated. In the third spring-damper-mass model, an active spring system for the leg of the rider was introduced with a variable spring stiffness and resting length in addition to a saddle spring with fixed material properties. The output of the models was compared with experimental data of sitting and rising trot and with the modern riding technique used by jockeys in racing. The models show which combinations of rider mass, spring stiffness and damping coefficient will result in a particular riding technique or other behaviours. Minimization of the peak force of the rider and the work of the horse resulted in an 'extreme' modern jockey technique. The incorporation of an active spring system for the leg of the rider was needed to simulate rising trot. Thus, the models provide insight into the biomechanical requirements a rider has to comply with to respond effectively to the movements of a horse.
A novel classification of planar four-bar linkages is presented based on the systematical variation of one, two or three bar lengths and studying the transmission properties (input-output curves) of the linkages. This classification is better suited to the study of biological systems than the classical Grashof-classification used in engineering as it considers the change of structural elements, in evolution for example, instead of evaluating the possibilities for the rotation of a particular bar. The mechanical features of a wide range of planar linkages in vertebrates, described by various authors, have been included in this classification. Examples are: skull-levation and jaw-protrusion mechanisms in fishes, reptiles and birds, the coral crushing apparatus of parrotfishes, and catapult-mechanisms in feeding pipefishes. Four-bar replacement mechanisms, e.g. crank-slider mechanisms in feeding systems of fishes and cam-mechanisms in mammalian limb-joints, and more complex linkages than four-bar ones, e.g. sixbar linkages and interconnected four-bar linkages in fish feeding mechanisms, are also discussed. In this way, an overview is obtained of the applicability of planar linkage theory in animal mechanics to mechanical functioning and the effect of possible variations of bar lengths and working ranges in evolution. Four-bar system analysis often provides a rigorous method of simplifying the study of complex biological mechanisms. The acceptable width-range of necessary and undesired hysteresis (‘play’) in biological linkages is also discussed.
