The effects of treadmill inclination and speed on the activity of two hindlimb muscles in the trotting horse

Electromyographic activity (EMG) was used to determine how hindlimb muscle activation patterns vary with speed and incline in the horse. EMG was recorded using surface electrodes over the gluteus medius and tensor fasciae latae muscles during treadmill locomotion at trot for different combinations of speed (3.5 to 6 m/s) and inclination (0, 3 and 6%). Raw EMG signals were processed to determine stride duration, activity onset and end, and integrated EMG (IEMG). Stride and stance phase duration decreased linearly with increasing speed. Stride duration was not influenced by the slope. Onset and end of muscle activity came significantly earlier in the stride cycle when speed increased and later when inclination changed from 0 to 6%. The relative duration of the burst (percentage of stride duration) increased as running speed increased, but tended to decrease with increasing slope. The IEMG of the muscles increased with increasing speed and slope, the largest increase being observed in the tensorfasciae latae. It is concluded that both increases in speed and inclination lead to an increase in the integrated electromyographic activity and hence to a higher workload of the 2 hindlimb muscles investigated.     

Electromyographic activity of the longissimus dorsi muscles in horses during trotting on a treadmill

OBJECTIVE: To use electromyography (EMG) to measure physiologic activity of the longissimus dorsi muscles of horses during trotting on a treadmill. ANIMALS: 15 adult horses (5 to 20 years old that weighed 450 to 700 kg) that did not have clinical signs of back pain. PROCEDURE: Data were recorded for each horse during trotting on a treadmill at speeds of 2.6 to 4.4 m/s. Surface electromyography was recorded bilaterally from the longissimus dorsi muscles at the levels of T12, T16, and L3. RESULTS: In each motion cycle, 2 EMG maxima were found at the end of the diagonal stance phases. The EMG activity peaked slightly later at L3 than at T12 and T16. Maximum EMG amplitudes were highest at T12 and decreased caudally, with mean +/- SD values of 4.51 +/- 1.20 mV at T12, 3.00 +/- 0.83 mV at T16, and 1.78 +/- 0.67 mV at L3. Mean minimum EMG activity was 1.30 +/- 0.63 mV at T12, 0.83 +/- 0.35 mV at T16, and 0.80 +/- 0.39 mV at L3. The relative amplitudes (ie, [maximum - minimum]/maximum) were 67 +/- 11% at T12, 66 +/- 8% at T16, and 71 +/- 8% at L3. CONCLUSIONS AND CLINICAL RELEVANCE: Activity of the longissimus dorsi muscles is mainly responsible for stabilization of the vertebral column against dynamic forces. The difference between minimum and maximum activity may allow application of this method as a clinical tool. Data reported here can serve as reference values for comparison with values from clinically affected horses.     

Trunk deformation in the trotting horse

Reasons for performing study: Estimates of the position of the centres of mass (CM) of body segments are usually extrapolated relative to bony landmarks as determined in cadaver studies. This extrapolation assumes that segments are rigid bodies. Since the trunk represents a large percentage of the total body mass in horses, violation of the rigid body assumption by the trunk segment has important consequences for studying the biomechanics of equine locomotion. Objectives: To assess the magnitude of error in CM position due to deformability of the trunk segment and the timing of these errors during the trotting stride. The hypothesis was that shape changes during a stride are repeatable and predictable. Methods: Forty skin markers were attached in a grid pattern on the trunks of 6 adult horses, with an additional marker attached to each hoof. The markers were tracked using an 8 camera motion analysis system. Each horse was tested at 10 different velocities during trotting. The CM of the trunk was calculated under the assumption of a rigid body, based on 5 spine markers and from the volume encompassed by the 40 markers. The difference between the 2 calculation methods quantifies the effect of trunk deformation on the position of the CM. Results: The trunk changed shape during locomotion in a repeatable manner resulting in cyclic changes in CM position. Amplitudes of the CM displacement due to trunk deformation were equal in magnitude in the transverse and longitudinal directions. In the vertical direction, the CM moved only at half the amplitude. Magnitudes were strongly horse‐dependent. Conclusions and potential relevance: Shape changes in the equine trunk segment in the horizontal plane should be taken into account when modelling locomotion of horses. Amplitudes are horse dependent, complicating the development of correction routines.     

The effect of three different head–neck positions on the average EMG activity of three important neck muscles in the horse

The Knowledge of muscle activity in common head–neck positions (HNPs) is a necessary precondition for making judgements on HNPs. The aim of the study was to record the surface electromyography activities of important muscles of the horse's neck in various HNPs. The electrical activities of the m. splenius, brachiocephalicus and trapezius were recorded on both sides. Five horses, both with and without a rider, were examined in all three gaits on both hands in three different HNPs: a ‘free’ position, a ‘gathered’ (head higher, neck more flexed) position with the noseline in front of the vertical and a ‘hyperflexed’ position. Averages of ten consecutive gait cycles in each HNP were evaluated and compared by standard statistical methods. No difference between ridden and unridden horses could be detected. The m. brachiocephalicus was in the hyperflexed position in all gaits significantly (p < 0.01) more active than in the gathered and free position, which were not significantly different. By contrast, the m. splenius was in the hyperflexed position less active than in the free position (p < 0.02), in which it always showed the highest activity. In walking, the muscle activities in the free and gathered positions deviated significantly (p < 0.01). The m. trapezius was in the hyperflexed posture during walking significantly less active than in the free (p < 0.01) and gathered (p < 0.01) positions with the strongest activities in the free position. Again, the free and gathered positions differed significantly (p < 0.01). In trot, the same pattern occured, although the gathered and hyperflexed positions did not differ significantly. In the canter, the activities of the m. trapezius showed no differences between HNPs. In HNPs with the noseline in front of the vertical, the muscles of the topline (m. splenius, m. trapezius) are activated and trained. In the hyperflexed position, however, a major muscle of the lower topline (m. brachiocephalicus) is activated and trained.     

Three-dimensional kinematics of the distal forelimb in horses trotting on a treadmill and effects of elevation of heel and toe

REASONS FOR PERFORMING STUDY: Comprehensive understanding of the 3-dimensional (3D) kinematics of the distal forelimb and precise knowledge of alterations induced by dorsopalmar foot imbalance remains incomplete because in vivo studies performed with skin markers do not measure the actual movements of the 3 digital joints. OBJECTIVE: To quantify the effects of 6 degree heel or toe wedges on the 3D movements of the 4 distal segments of the forelimb in horses trotting on a treadmill. METHODS: Three healthy horses were equipped with ultrasonic markers fixed surgically to the 4 distal segments of the left forelimb. The 3D movements of these segments were recorded while horses were trotting on a treadmill. Rotations of the digital joints were calculated by use of a joint coordinate system. Data obtained with 6 degree heel or toe wedges were compared to those obtained with flat standard shoes. RESULTS: Use of heel wedges significantly increased maximal flexion and decreased maximal extension of the proximal (PIPJ) and distal (DIPJ) interphalangeal joints. Inverse effects (except for PIPJ maximal extension) were observed with the toe wedges. In both cases, neither flexion-extension of the metacarpophalangeal joint nor extrasagittal motions of the digital joints were statistically different between conditions. CONCLUSIONS: At a slow trot on a treadmill, heel and toe wedges affect the sagittal plane kinematics of the interphalangeal joints. POTENTIAL RELEVANCE: Better understanding of the actual effects of toe and heel wedges on the 3D kinematics of the 3 digital joints may help to improve clinical use of sagittal alteration of hoof balance in the treatment of distal forelimb injuries.     

Basic three-dimensional kinematics of the vertebral column of horses trotting on a treadmill

OBJECTIVE: To determine movements of the vertebral column of horses during normal locomotion. ANIMALS: 5 young Dutch Warmblood horses that did not have signs of back problems or lameness. PROCEDURE: Kinematics of 8 vertebrae (T6, T10, T13, T17, L1, L3, L5, and S3) and both tuber coxae were determined, using bone-fixated markers. Measurements were recorded when the horses were trotting on a treadmill at a constant speed of 4.0 m/s. RESULTS: Flexion-extension and axial rotation were characterized by a double sinusoidal pattern of motion during 1 stride cycle, whereas lateral bending was characterized by 1 peak and 1 trough. Ranges of motion for all vertebrae were: flexion-extension, 2.8 degrees to 4.9 degrees; lateral bending, 1.9 degrees to 3.6 degrees; axial rotation, 4.6 to 5.8 degrees, except for T10 and T13, where the amount of axial rotation decreased to 3.1 degrees and 3.3 degrees, respectively. CONCLUSION AND CLINICAL RELEVANCE: During locomotion, 3 types of rotations are evident in the thoracolumbar vertebrae. Regional differences are observed in the shape and timing of the rotations. These differences are related to actions of the limbs. The method described here for direct measurement of vertebral column motion provides insights into the complex movements of the thoracolumbar portion of the vertebral column in trotting horses. Information on normal kinematics is a prerequisite for a better understanding of abnormal function of the vertebral column in horses.     

The biomechanical construction of the horse's body and activity patterns of three important muscles of the trunk in the walk,trot and canter

The activity patterns of trunk muscles are commonly neglected, in spite of their importance for maintaining body shape. Analysis of the biomechanics of the trunk under static conditions has led to predictions of the activity patterns. These hypotheses are tested experimentally by surface electromyography (EMG). Five horses, with and without a rider, were examined in the walk, trot and canter. Footfall was synchronised with EMG by an accelerometer. Averages of ten consecutive cycles were calculated and compared by statistical methods. The start and stop times of the muscle activities of 5–10 undisturbed EMG plots were determined and the averages and standard deviations calculated. In walking, muscle activities are minor. Electromyography (EMG) activity was increased in the m. rectus during the three‐limb support. When the bending moments assume their greatest values, for example while the horses' mass is accelerated upward (two times earth acceleration) in the diagonal support phases in trot and canter the m. rectus, connecting the sternum with the pubic bone is most active. The m. obl. externus is most active when the torsional and bending moments are greatest during the same support phases, but not bilaterally, because the forces exerted on one side by the (recorded) m. obl. externus are transmitted on the other side by the (not recorded) m. obl. internus. While the hindlegs touch the ground in the trot and canter, ground reaction forces tend to flex the hip joint and the lumbar spine. Therefore, the vertebral column needs to be stabilised by the ipsilateral m. longissimus dorsi, which in fact can be observed. As a whole, our EMG data confirm exactly what has been predicted by theoretical analysis.     

Electromyographic activity of the longissimus dorsi muscles in horses when walking on a treadmill

The pattern of electromyographic activity of the equine long back muscle at the walk has not yet been reported. The aim of this study was to use surface electromyography to measure activity of the longissimus dorsi muscles of horses walking on a treadmill. Fifteen horses without back pain were used and electromyographs were recorded bilaterally from the longissimus dorsi muscles at the level of T12, T16 and L3. Mean electromyograph activity and mean motion were calculated for each horse. At the walk, only one maximum activity for each longissimus dorsi muscle was detected during each motion cycle and this was highest at T12 and lowest at L3. Activity of the longissimus dorsi muscles at the walk is mainly responsible for stabilisation of the vertebral column against dynamic forces. At T12 the high maximum activity could contribute to the development of muscle pain at this site.     

Influence of trotting and galloping exercises on erythrogram of andalusian horse stallions

Possible alterations in the erythrogram and in red blood cell volume indices were studied in ten Andalusian stallions subjected to two different types of exercise (trotting and galloping). For this purpose, the changes in these blood parameters were measured during resting, immediately after the exercise finished, and at 5, 10 and 30 min. of recovery.From the results it was deduced that the red blood cell count (RBC), the hematocrit value (PCV) and the concentration of hemoglobin (HB) increased significantly (p≤0.05) after finishing both types of exercise, with a greater increase with galloping. The return to baseline values was faster for trotting than for galloping. However, the RBC volume indices (mean corpuscular volume, mean corpuscular hemoglobin and mean corpuscular hemoglobin concentration) did not undergo any significant changes with either type of exercise.     

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.     

Individual speed dependency of forelimb lameness in trotting horses

Using a system for motion analysis, linear correlation of speed and forelimb lameness was measured in 16 horses trotting on a treadmill at a minimum of three different trotting speeds. Forelimb lameness was determined as asymmetry of vertical head motion during left and right forelimb stance.In seven horses with a moderate forelimb lameness (head motion asymmetry >40%), lameness increased significantly with trotting speed. In a further seven horses with mild or subclinical forelimb lameness (head motion asymmetry <40%) and in two horses with a moderate forelimb lameness, no significant correlation between speed and motion asymmetry was found.The results indicate that moderate forelimb lameness measured as head motion asymmetry depends on the speed at which the measurements are taken. If head motion asymmetry is measured at two trotting speeds, it can be standardized to any speed within the trotting speed range.     

Vertical ground reaction force-time histories of sound Warmblood horses trotting on a treadmill

The objective of this study was to establish representative treadmill ground reaction force (GRF) and interlimb co-ordination time data of clinically sound horses at the trot. It was anticipated that these normative standards would provide a reference data base against which lame horses could be compared. GRF-time histories were collected from 30 Warmblood riding horses with easy, wide natural gaits. Data were recorded of all four limbs simultaneously by the use of an instrumented treadmill. A total of 912 stride cycles per limb were analysed for force, time and spatial parameters and were averaged. The shape and amplitude of the treadmill force curves were very similar to force traces recorded with a stationary force plate. The horses showed a high degree of symmetry in all investigated parameters (95% reference interval of left-right asymmetry +/-1.8-6.8%). No significant differences were found between left and right mean values. Intra-individual coefficients of variance of the various parameters did not exceed 2.7%. Inter-individual coefficients of variance were 2.5-3.5 times larger than the respective intra-individual coefficients. An instrumented treadmill provides a number of decisive advantages, such as time-efficient data acquisition of all four feet simultaneously over successive strides, or the high regularity of the horse's gait pattern at controlled velocities, which allow the clinical assessment of locomotor performance of horses.     

Computer-assisted kinematic evaluation of induced compensatory movements resembling lameness in horses trotting on a treadmill

OBJECTIVE: To characterize compensatory movements of the head and pelvis that resemble lameness in horses. ANIMALS: 17 adult horses. PROCEDURE: Kinematic evaluations were performed while horses trotted on a treadmill before and after shoe-induced lameness. Lameness was quantified and the affected limb determined by algorithms that measured asymmetry in vertical movement of the head and pelvis. Induced primary lameness and compensatory movements resembling lameness were assessed by the Friedman test. Association between induced lameness and compensatory movements was examined by regression analysis. RESULTS: Compensatory movements resembling lameness in the ipsilateral forelimb were seen with induced lameness of a hind limb. There was less downward and less upward head movement during and after the stance phase of the ipsilateral forelimb. Doubling the severity of lameness in the hind limb increased severity of the compensatory movements in the ipsilateral forelimb by 50%. Compensatory movements resembling lameness of the hind limb were seen after induced lameness in a forelimb. There was less upward movement of the pelvis after the stance phase of the contralateral hind limb and, to a lesser extent, less downward movement of the pelvis during the stance phase of the ipsilateral hind limb. Doubling the severity of lameness in the forelimb increased compensatory movements of the contralateral hind limb by 5%. CONCLUSIONS AND CLINICAL RELEVANCE: Induced lameness in a hind limb causes prominent compensatory movements resembling lameness in the ipsilateral forelimb. Induced lameness in a forelimb causes slight compensatory movements resembling lameness in the ipsilateral and contralateral hind limbs.     

Changes in kinematic variables observed during pressure-induced forelimb lameness in adult horses trotting on a treadmill

OBJECTIVE: To determine whether kinematic changes induced by heel pressure in horses differ from those induced by toe pressure. ANIMALS: 10 adult Quarter Horses. PROCEDURE: A shoe that applied pressure on the cuneus ungulae (frog) or on the toe was used. Kinematic analyses were performed before and after 2 levels of frog pressure and after 1 level of toe pressure. Values for stride displacement and time and joint angles were determined from horses trotting on a treadmill. RESULTS: The first level of frog pressure caused decreases in metacarpophalangeal (fetlock) joint extension during stance and increases in head vertical movement and asymmetry. The second level of frog pressure caused these changes but also caused decreases in stride duration and carpal joint extension during stance as well as increases in relative stance duration. Toe pressure caused changes in these same variables but also caused maximum extension of the fetlock joint to occur before midstance, maximum hoof height to be closer to midswing, and forelimb protraction to increase. CONCLUSION AND CLINICAL RELEVANCE: Decreased fetlock joint extension during stance and increased head vertical movement and asymmetry are sensitive indicators of forelimb lameness. Decreased stride duration, increased relative stance duration, and decreased carpal joint extension during stance are general but insensitive indicators of forelimb lameness. Increased forelimb protraction, hoof flight pattern with maximum hoof height near midswing, and maximum fetlock joint extension in cranial stance may be specific indicators of lameness in the toe region. Observation of forelimb movement may enable clinicians to differentiate lameness of the heel from lameness of the toe.