Thomas Wiestner

Compensatory load redistribution of horses with induced weightbearing hindlimb lameness trotting on a treadmill

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.

Relationships of Body Weight, Body Size, Subject Velocity, and Vertical Ground Reaction Forces in Trotting Dogs

OBJECTIVE To evaluate the relationship of body weight (BW) and size, dog velocity, and vertical ground reaction forces (GRF) from a large number of dogs of various sizes. STUDY DESIGN Clinical research. ANIMALS Orthopedically healthy dogs (n=129) METHODS BW and dog size, represented as height at the withers (WH), were obtained. Stance times (ST), vertical impulses (VI), and peak vertical forces (PVF) of thoracic and pelvic limbs were measured on a force plate at controlled trotting speed. They were evaluated against BW and WH using linear regression analysis in absolute (nonnormalized) values, and when normalized to BW and/or body size according to the theory of dynamic similarity. Relative velocities were calculated for each dog. RESULTS Absolute ST, VI, and PVF showed strong positive correlations with BW and/or body size. When GRFs were normalized to BW, correlations with body size were markedly reduced, but remained positive for VI, and turned negative for PVF. Normalizing the time-dependent variables (ST and VI) also to WH eliminated most size influence. A small dependency of fully normalized GRF on body size remained that was because of differences in relative velocity between dogs of different sizes. Reference values for the fully normalized data are given. CONCLUSIONS The inherent relationship between BW, body size, dog velocity, and vertical GRF was demonstrated. CLINICAL RELEVANCE BW, body size, and relative dog velocity must be accounted for when wanting to obtain GRF variables that are comparable between different dogs.Objective: To evaluate the relationship of body weight (BW) and size, dog velocity, and vertical ground reaction forces (GRF) from a large number of dogs of various sizes. Study Design: Clinical research. Animals: Orthopedically healthy dogs (n=129) Methods: BW and dog size, represented as height at the withers (WH), were obtained. Stance times (ST), vertical impulses (VI), and peak vertical forces (PVF) of thoracic and pelvic limbs were measured on a force plate at controlled trotting speed. They were evaluated against BW and WH using linear regression analysis in absolute (nonnormalized) values, and when normalized to BW and/or body size according to the theory of dynamic similarity. Relative velocities were calculated for each dog. Results: Absolute ST, VI, and PVF showed strong positive correlations with BW and/or body size. When GRFs were normalized to BW, correlations with body size were markedly reduced, but remained positive for VI, and turned negative for PVF. Normalizing the time-dependent variables (ST and VI) also to WH eliminated most size influence. A small dependency of fully normalized GRF on body size remained that was because of differences in relative velocity between dogs of different sizes. Reference values for the fully normalized data are given. Conclusions: The inherent relationship between BW, body size, dog velocity, and vertical GRF was demonstrated. Clinical Relevance: BW, body size, and relative dog velocity must be accounted for when wanting to obtain GRF variables that are comparable between different dogs.

Relationship between saddle pressure measurements and clinical signs of saddle soreness at the withers.

REASONS FOR PERFORMING THE STUDY Similar to human decubitus ulcers, local high pressure points from ill-fitting saddles induce perfusion disturbances of different degrees resulting in tissue hypoxia and alteration in sweat production. OBJECTIVE To relate the different clinical manifestations of saddle sores to the magnitude of saddle pressures at the location of the withers. METHODS Sixteen horses with dry spots after exercise (Group A) and 7 cases presented with acute clinical signs of saddle pressure in the withers area (Group B) were compared with a control group of 16 sound horses with well fitting saddles (Group C). All horses underwent a saddle pressure measurement at walk, trot and canter. Mean and maximal pressures in the area of interest were compared between groups within each gait. RESULTS Mean pressures differed significantly between groups in all 3 gaits. Maximal pressure differed between groups at trot; at walk and canter, however, the only significant difference was between Group C and Groups A and B, respectively, (P > 0.05). Mean and maximal pressures at walk in Group A were 15.3 and 30.6 kPa, in Group B 24.0 and 38.9 kPa and in Group C 7.8 and 13.4 kPa, respectively; at trot in Group A 18.1 and 43.4 kPa, in Group B 29.7 and 53.3 kPa and in Group C 9.8 and 21.0 kPa, respectively; and at canter in Group A 21.4 and 48.9 kPa, in Group B 28.6 and 56.0 kPa and in Group C 10.9 and 24.7 kPa, respectively. CONCLUSION The study shows that there is a distinguishable difference between the 3 groups regarding the mean pressure value, in all gaits.

Effect of dog breed and body conformation on vertical ground reaction forces, impulses, and stance times.

OBJECTIVES To assess whether fully normalised vertical ground reaction forces and stance times obtained at a trot depend on dog breed or body conformations. METHODS Peak vertical forces (PVF), vertical impulses (VI), stance times (ST), and ratio of forelimb impulse to total impulse (RVI) of 54 dogs of seven different breeds were normalised to body weight and body size according to the theory of dynamic similarity, and were tested for differences between breeds. Breeds were Borzoi, Bernese Mountain dog, Great Dane, Labrador Retriever, Landseer, Rhodesian Ridgeback, and Rottweiler. Body length ratio (BLR) and body mass index (BMI) were also compared between breeds. RESULTS Significant differences between breeds were found for the normalised forelimb PVF, VI and ST, and hindlimb PVF. Looking at individual breeds, it was most evident that Borzois had a lower forelimb VI, and a higher hindlimb PVF than the other breeds. This resulted in Borzois having a lower RVI compared to other dogs, indicating a more caudally located centre of gravity. Only a few differences in gait parameters were found between other dog breeds. The BMI was significantly lower in Borzois than in other breeds, but was otherwise not associated with gait parameters. CLINICAL SIGNIFICANCE Force plate data of dogs of different breeds are not necessarily comparable, even after full normalisation to body weight and body size. Group comparisons should only be made when the groups consist of breeds with similar body conformations.

Velocity-dependent changes of time, force and spatial parameters in Warmblood horses walking and trotting on a treadmill

REASONS FOR PERFORMING STUDY Gait analysis parameters are sensitive to alterations in velocity. For comparison of nonspeed-matched data, the velocity dependency needs to be known. OBJECTIVES To describe the changes in gait pattern and determine the relationships between stride duration, vertical impulse, contact time and peak vertical force within a range of walking and trotting speeds. METHODS Thirty-eight nonlame Warmblood horses were subjected to an incremental speed test. The spans of speed were adjusted individually to each horse and ranged from 1.1-2.1 m/s at walk and from 2.5-5.8 m/s at trot. Time, force and spatial parameters of each limb were measured with an instrumented treadmill and analysed with regression analysis using velocity as the independent variable. RESULTS At a slow walk the shape of the force curve was generally single-peaked in the fore- and trapezoidal in the hindlimbs. With increasing speed, the curves turned into the typical double-peaked shape with a higher second peak in the fore- and a higher first peak in the hindlimbs. With increasing velocity, stride duration, stance durations and limb impulses of the fore- and hindlimbs decreased in both gaits (r2 > 0.92). Increasing speed caused a weight shift to the forehand (walk: from 56 to 59%; trot: from 55 to 57%). Despite decreasing limb impulses, peak vertical forces increased in both gaits (r2 > 0.83). The suspension duration of the trot increased with faster velocities and reached a plateau of around 90 ms at the highest speeds. At a slow trot, the forelimbs impacted first and followed the hindlimbs at lift-off; with increasing speed, the horses tended to impact earlier with the hindlimbs. Contralateral symmetry indices of all parameters remained unchanged. CONCLUSIONS Subject velocity affects time, force and spatial parameters. Knowing the mathematical function of these interdependencies enables correction of nonspeed-matched data.

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

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.

Relationship between the forces acting on the horse's back and the movements of rider and horse while walking on a treadmill.

REASONS FOR PERFORMING STUDY The exact relationship between the saddle pressure pattern during one stride cycle and the movements of horse and rider at the walk are poorly understood and have never been investigated in detail. HYPOTHESIS The movements of rider and horse account for the force distribution pattern under the saddle. METHOD Vertical ground reaction forces (GRF), kinematics of horse and rider as well as saddle forces (FS) were measured synchronously in 7 high level dressage horses while being ridden on an instrumented treadmill at walk. Discrete values of the total saddle forces (FStot) were determined for each stride and related to kinematics and GRF. The pressure sensitive mat was divided into halves and sixths to assess the force distribution over the horses back in more detail. Differences were tested using a one sample t test (P < 0.05). RESULTS FStot of all the horses showed 3 peaks (P1-P3) and 3 minima (M1-M3) in each half-cycle, which were systematically related to the footfall sequence of the walk. Looking at the halves of the mat, force curves were 50% phase-shifted. The analysis of the FS of the 6 sections showed a clear association to the riders and horses movements. CONCLUSION The saddle force distribution during an entire stride cycle has a distinct pattern although the force fluctuations of the FStot are small. The forces in the front thirds were clearly related to the movement of the front limbs, those in the mid part to the lateral flexion of the horses spine and the loading of the hind part was mainly influenced by the axial rotation and lateral bending of the back. POTENTIAL RELEVANCE These data can be used as a reference for comparing different types of saddle fit.

Saddle pressure patterns of three different training saddles (normal tree, flexible tree, treeless) in Thoroughbred racehorses at trot and gallop

REASONS FOR PERFORMING STUDY To a large extent the success of a racehorse depends on effective and health preserving training methods. An important issue is the prevention of back pain. The influence of different types of training saddles (normal tree: S(A), treeless: S(B), flexible tree: S(C)) on the saddle pressure patterns in racehorses have not previously been investigated. It is commonly assumed that S(A) limits the motion of the back especially in the lower thoracic region during gallop. HYPOTHESIS S(A) produces higher pressures in the caudal part of the saddle at trot (rising trot), canter and gallop (both in a jockey seat) compared to S(B) and S(C). METHODS Saddle pressures were measured in 8 racehorses ridden on a training track at trot (3.5 m/s), canter (6.4 m/s) and gallop (12.6 m/s). Each horse performed the protocol with each saddle. To analyse the pressure distribution over the horses back the pressure picture was divided into thirds (TD(front), TD(mid), TD(hind)). The stride-mean loaded areas, forces and mean and peak pressures were determined. RESULTS At canter and gallop, all 3 saddles were mainly loaded in TD(front) (>80% of the riders weight), with a decreasing gradient to TD(mid) and TD(hind) (<3%), which was least pronounced in S(C). At trot, the load was shifted towards TD(mid) and TD(hind) (10-15%, each). High peak pressures occurred in TD(front) at canter and gallop and in TD(hind) at trot. CONCLUSIONS The type of tree had no influence on the pressure picture of the caudal third at gallop. The high peak pressures observed in TD(hind) at trot in all saddles may limit the activity of the horses back, which is of particular importance since trot is an integral part of the daily work.

Performance parameters and post exercise heart rate recovery in Warmblood sports horses of different performance levels.

REASONS FOR PERFORMING STUDY Standardised exercise tests are used for fitness evaluation of sports horses. Standards are described for Thoroughbreds and Standardbreds; however, limited information is available for Warmbloods. OBJECTIVES To establish normative standards of performance parameters and heart rate recovery (HRR) in Warmblood riding horses of different levels of fitness using a submaximal incremental exercise test (SIET) performed on a treadmill. METHODS A SIET was carried out with 29 healthy and treadmill-accustomed Warmbloods: eleven 3-day event horses (TDE) and 18 horses from the National Equestrian Centre (NEC) competing in amateur jumping and/or dressage events. After a warm-up phase, horses performed 2 stages at trot and 3-5 stages at gallop at 6% incline. The first stage lasted 120 s, all others 90 s. Velocity (V) and heart rate (HR) were measured continuously and blood lactate concentration (LAC) at the end of each exercise stage. V at HR 150 and 200 beats/min (V(150), V(200)), V and HR at 2 and 4 mmol/l LAC (V(2), V(4) and HR(2), HR(4), respectively) were calculated and compared between discipline groups. For reference values, horses were divided on the basis of the V(4) -results in good (GP) and average performers (AP) (performance groups). Five minute passive HRR was compared between performance groups. Fifteen NEC horses were retested within 1-3 months. Groups were compared with t tests and P < 0.05 considered significant. RESULTS Three-day event horses had higher V(150), V(2) and V(4) values than NEC. GP had higher values in all performance parameters compared to AP. No differences were found between test and retest. GP mean recovery HR was different from that of AP from 120 s of recovery onwards. CONCLUSION Treadmill SIETs are suitable to objectify aerobic capacity in Warmblood riding horses. Normative standards were assessed for well and averagely-trained horses. The results can be referred to when diagnosing patients with exercise intolerance.

Kinetics and kinematics of the passage

REASONS FOR PERFORMING STUDY The load acting on the limbs and the load distribution between fore- and hindlimbs while performing specific dressage exercises lack objective assessment. HYPOTHESIS The greater a horses level of collection, the more load is shifted to the rear and that during the passage the vertical load on the limbs increases in relation to the accentuated vertical movement of the centre of mass. METHODS Back and limb kinematics, vertical ground reaction force and time parameters of each limb were measured in 6 Grand Prix dressage horses performing on an instrumented treadmill at the trot and the passage. Horses were ridden by their own professional rider. RESULTS At the passage, horses moved at a slower speed (-43.2%), with a lower stride frequency (-23.6%) and, therefore, higher stride impulses (+31.0%). Relative stance duration of fore- and hindlimbs and suspension duration remained unchanged. While at the trot the diagonal limbs impacted almost simultaneously, the hindlimbs always impacted first at the passage; the time dissociation between landing and lift-off remained unchanged. Because of the prolonged stride duration, stride impulse and consequently limb impulses were higher at the passage in the fore- as well as in the hindlimbs (+24.8% and +39.9%, respectively). Within the diagonal limb pair, load was shifted from the forehand to the hindquarters (percentage stride impulse carried by the forehand -4.8%). Despite the higher impulses, peak vertical forces in the fore- and hindlimbs remained unchanged because of the prolonged absolute stance durations in fore- and hindlimbs (+28.1% and +32.2%, respectively). CONCLUSIONS Based on the intralimb timing, the passage closely resembles the trot. Compared to other head-neck positions, the higher degree of collection resulted in a pronounced shift in impulse towards the hindquarters. Despite the higher limb impulses, peak forces acting on the limbs were similar to those observed at the trot. POTENTIAL CLINICAL RELEVANCE An understanding of load distribution between fore- and hindlimbs in relation to different riding techniques is crucial to prevent wear-and-tear on the locomotor apparatus.