An exploration of the influence of diagonal dissociation and moderate changes in speed on locomotor parameters in trotting horses

Abstract

Background. Although the trot is described as a diagonal gait, contacts of the diagonal pairs of hooves are not usually perfectly synchronized. Although subtle, the timing dissociation between contacts of each diagonal pair could have consequences on gait dynamics and provide insight into the functional strategies employed. This study explores the mechanical effects of different diagonal dissociation patterns when speed was matched between individuals and how these effects link to moderate, natural changes in trotting speed. We anticipate that hind-first diagonal dissociation at contact increases with speed, diagonal dissociation at contact can reduce collision-based energy losses and predominant dissociation patterns will be evident within individuals.Methods. The study was performed in two parts: in the first 17 horses performed speed-matched trotting trials and in the second, five horses each performed 10 trotting trials that represented a range of individually preferred speeds. Standard motion capture provided kinematic data that were synchronized with ground reaction force (GRF) data from a series of force plates. The data were analyzed further to determine temporal, speed, GRF, postural, mass distribution, moment, and collision dynamics parameters.Results. Fore-first, synchronous, and hind-first dissociations were found in horses trotting at (3.3 m/s ± 10%). In these speed-matched trials, mean centre of pressure (COP) cranio-caudal location differed significantly between the three dissociation categories. The COP moved systematically and significantly (P = .001) from being more caudally located in hind-first dissociation (mean location = 0.41 ± 0.04) through synchronous (0.36 ± 0.02) to a more cranial location in fore-first dissociation (0.32 ± 0.02). Dissociation patterns were found to influence function, posture, and balance parameters. Over a moderate speed range, peak vertical forelimb GRF had a strong relationship with dissociation time (R = .594; P < .01) and speed (R = .789; P < .01), but peak vertical hindlimb GRF did not have a significant relationship with dissociation time (R = .085; P > 0.05) or speed (R = .223; P = .023).Discussion. The results indicate that at moderate speeds individual horses use dissociation patterns that allow them to maintain trunk pitch stability through management of the cranio-caudal location of the COP. During the hoof-ground collisions, reduced mechanical energy losses were found in hind-first dissociations compared to fully synchronous contacts. As speed increased, only forelimb vertical peak force increased so dissociations tended towards hind-first, which shifted the net COP caudally and balanced trunk pitching moments.

Ground reaction forces of elite dressage horses in collected trot and passage

“…The higher hindlimb propulsive impulse in passage could contribute to a nose-up moment around the COM that would lift the forehand (Hobbs et al, 2016). In passage the forelimb exerts a braking force while the hindlimb simultaneously exerts a propulsive longitudinal force through much of stance (Figure 2), which results in a marked convergence of their sagittal plane GRF vectors (Figure 3).…”

Peer Review #2 of "A simple method of equine limb force vector analysis and its potential applications (v0.1)"

“…In horses, the large forelimb vertical impulses elevate the COM (Weishaupt et al, 2009;Clayton, Schamhardt and Hobbs, 2017; and increase nose-up pitching moments (Hobbs, Bertram and Clayton, 2016). Asymmetries between left and right limbs and diagonals may or may not be repeated consistently from step to step, as they reflect the need for subtle adjustments of balance within a single stride (Hobbs, Bertram and Clayton, 2016). This is particularly evident in the hindlimbs, as no significant differences were found in the group analyses.…”

“…The functional role of the forelimbs is to provide a mechanism to alter the centre of mass (COM) trajectory from forwards and downwards at diagonal contact to forwards and upwards at diagonal lift off (Bertram and Gutmann, 2008). In horses, the large forelimb vertical impulses elevate the COM (Weishaupt et al, 2009;Clayton, Schamhardt and Hobbs, 2017; and increase nose-up pitching moments (Hobbs, Bertram and Clayton, 2016). Asymmetries between left and right limbs and diagonals may or may not be repeated consistently from step to step, as they reflect the need for subtle adjustments of balance within a single stride (Hobbs, Bertram and Clayton, 2016).…”

“…Statistical analyses are then used to detect differences between horses, limbs or experimental conditions. This approach has facilitated the description of normative GRF values at different gaits (Clayton, Schamhardt and Hobbs, 2017;Khumsap et al, 2001;Merkens et al, 1986Merkens et al, , 1993aMerkens et al, , 1993b) and speeds (Dutto et al, 2004;Hobbs, Bertram and Clayton, 2016). Changes in the typical force patterns and values have been reported in association with lameness (e.g.…”

“…Back et al, 2007;Ishihara et al, 2005;Khumsap et al, 2003;McLauchlan et al, 1996;Weishaupt et al, 2004aWeishaupt et al, , 2004bWeishaupt et al, , 2006Weishaupt, 2008), farriery modifications (e.g. Riemersma et al, 1996), local anesthesia (Bidwell et al, 2004), asymmetry (Wiggers et al, 2015) and training (Hobbs, Bertram and Clayton, 2016;. Left-right asymmetries in peak vertical GRF are the most specific and sensitive GRF variable for detecting lameness (Ishihara et al, 2005) and have been applied in establishing asymmetry thresholds for lameness diagnosis (Weishaupt, 2008).…”