The jump shot - a biomechanical analysis focused on lateral ankle ligaments.

Handball is one of the top four athletic games with highest injury risks. The jump shot is the most accomplished goal shot technique and the lower extremities are mostly injured. As a basis for ankle sprain simulation, the aim of this study was to extend the ankle region of an existing musculoskeletal full-body model through incorporation of three prominent lateral ankle ligaments: ligamentum fibulotalare anterius (LFTA), ligamentum fibulotalare posterius (LFTP), ligamentum fibulocalcaneare (LFC). The specific objective was to calculate and visualise ligament force scenarios during the jumping and landing phases of controlled jump shots. Recorded kinematic data of performed jump shots and the corresponding ground reaction forces were used to perform inverse dynamics. The calculated peak force of the LFTA (107 N) was found at maximum plantarflexion and of the LFTP (150 N) at maximum dorsiflexion. The peak force of the LFC (190 N) was observed at maximum dorsiflexion combined with maximum eversion. Within the performed jump shots, the LFTA showed a peak force (59 N to 69 N) during maximum plantarflexion in the final moment of the lift off. During landing, the force developed by the LFTA reached its peak value (61 N to 70 N) at the first contact with the floor. After that, the LFTP developed a peak force (70 N to 118 N). This model allows the calculation of forces in lateral ankle ligaments. The information obtained in this study can serve as a basis for future research on ankle sprain and ankle sprain simulation.

A preliminary model study of the equine back including activity of longissimus dorsi muscle.

REASONS FOR PERFORMING STUDY: Identifying the underlying problem of equine back pain and diseases of the spine are significant problems in veterinary orthopaedics. A study to validate a preliminary biomechanical model of the equine back based on CT images including longissimus dorsi (LD) muscle is therefore important. OBJECTIVES: Validation of the back model by comparing the shortening of LD muscles in the model with integrated EMG (IEMG) at stance during induced lateral flexion of the spine. METHODS: Longissimus dorsi muscle activity at stance has been used for validation. EMG electrodes were placed laterally at the level of T12, T16 and L3. Reflective markers have been attached on top of the spinous processes T5, T12, T16, L1 and the sacral bone (OS1, OS2) for motion tracking analysis. A virtual model of the equine's back (T1-S5) was built with inclusion of a simplified LD muscle by 2 separate contours left and right of the spine, starting at tuber coxae laterally and attaching to the spinous process T5 medially. Shortening of LD during induced lateral flexion caused by the kinematic data (input) was compared to the 3 EMG signals (T12, T16 and L3) on the active side via correlation. RESULTS: Pearson correlation coefficient between IEMG and shortening length of LD in the model was (mean ± s.d.) 0.95 ± 0.07 for the left side and 0.91 ± 0.07 for the right side of LD. CONCLUSIONS: Activity of the LD muscles is mainly responsible for stabilisation of the vertebral column with isometric muscle contraction against dynamic forces in walk and trot. This validation requires muscle shortening in the back, like induced lateral flexion at stance. The length of the shortening muscle model and the IEMG show a linear relationship. These findings will help to model the LD for forward simulations, e.g. from force to motion.

Influence of shoes with different weights on the motion of the limbs in Icelandic horses during toelt at different speeds.

REASON FOR PERFORMING STUDY: Weight boots are commonly used for Icelandic horses to increase the height of the flight arc of the forelimbs in toelt. OBJECTIVE: To show the influence of weights and toelting speed on the height of the swing phase. MATERIALS AND METHODS: Eight Icelandic horses (mean ± s.d. 12 ± 3 years old, 369 ± 46 kg) were used. Reflecting makers were placed on the dorsal side of each hoof. The motion was collected with a kinematic system (10 cameras, 120 Hz sample rate, 1.3 Mpixels resolution). The horses were ridden in toelt by 2 experienced riders on a treadmill at 2 different speeds (2.96 m/s ± 0.30 and 4.10 m/s ± 0.32). At each speed the horses were measured wearing no boots, light boots (170 g) and heavy boots (280 g) on both fore hooves. The measurement sequence was varied between horses. A Kolmogorov-Smirnov test was carried out to test for normal distribution of data and ANOVA for repeated measurements were used to compare differences (P < 0.05). RESULTS: The weight as well as the speed of toelt had a significant influence on the height of the flight arc. At the lower speed, the mean ± s.d. height was 163 ± 55 mm, whereas at the higher speed the mean height was 228 ± 60 mm. The heavy weights increased the mean height at the lower speed from 152 ± 38 to 169 ± 48 mm and at the higher speed from 214 ± 60 to 245 ± 60 mm. CONCLUSIONS: This investigation shows that Icelandic horses can be expected to show a better toelt in competitions with weights, and ridden at a higher speed. For muscle adaptation to occur, weights should therefore be used during competitions and training.

Electromyography activity of the equine splenius muscle and neck kinematics during walk and trot on the treadmill.

REASONS FOR PERFORMING STUDY: Skeletal muscle activity can be concentric or eccentric, anisometric or isometric and correlation of the equine splenius muscle activity with the movement of its effector joints at walk and trot has not yet been fully characterised. OBJECTIVE: Investigating activity of the splenius muscle together with kinematics of head and cranial neck at walk and trot. MATERIALS AND METHODS: Kinematics and surface electromyography were measured in 6 horses (8-20-years-old, 450-700 kg) without signs of neck pain. Markers were placed on left and right crista facialis, and on left and right cervical vertebrae 1 and 3. Head and neck angle was calculated in sagittal and horizontal planes. Electrodes were placed over both splenius muscles at the level of C2. Left and right muscle activity was compared using Student t test for paired samples and correlations calculated using Pearson correlation coefficient. Significance was set at P < 0.05. RESULTS: In all horses, maximum surface electromyography (sEMG) values at the trot were higher than at the walk. The intraindividual differences between maximum and minimum values of the EMG ranged from 45-127 mV in walk and from 154-524 mV in trot. Flexion-extension C1 angle changed by 43° in walk and 27° in trot. For each motion cycle, 2 EMG maxima were found in both gaits, occurring just prior to maximum extension of the C1 angle. Lateral bending at C1 angle changed by 16° in walk and 17° in trot and EMG reached maximum values bilaterally during maximum lateral bending at walk. CONCLUSIONS: The splenius muscle reaches maximum activity at the beginning of the forelimb stance phases in trot, indicating functional stabilisation against flexion of the head and neck. Unilateral activity of the splenius muscle representing stabilisation against lateral movement was not found.

A preliminary modelling study on the equine cervical spine with inverse kinematics at walk.

REASON FOR PERFORMING STUDY: The motion of the atlanto-occipital, cervical vertebral and cervicothoracic joints play an important role in equestrian sports and they are also common sites for lesions limiting performance in horses. OBJECTIVES: To calculate inverse kinematics based on cervical vertebral motion and to develop a model close to the measured neck movements. MATERIALS AND METHODS: Measurements were recorded in 6 horses without neck pain. Reflective markers were placed on both cristae facialis, both sides of cervical vertebra 1, 3 and 6 on the withers and hooves. The neck model was reconstructed from CT scans of the osseus structures and was developed in SIMM (Software for Interactive Musculoskeletal Modelling). Inverse kinematics calculation was done in OpenSim. Three degrees of freedom: Flexion-extension (FE), axial rotation (AR) and lateral bending (LB) were considered. The simulated motion was generated from the recorded motion of the skin markers. The differences in angular range of motion (ROM) of the joints were analysed using paired sample t tests. RESULTS: From the model, the smallest FE ROM was in the C5-C6 joint (2° ± 1°) and the largest was in the C3-C4 joint (11° ± 5°). The smallest AR ROM was in the C5-C6 joint (2° ± 1°) and largest AR ROM was in the atlantoaxial joint (7° ± 2°). The smallest LB ROM was in the C5-C6 joint (2° ± 1°) and the largest LB ROM was in the cervicothoracic joint (18° ± 5°). There were significant differences between the ROM of joints in 51 of 168 comparisons (P < 0.05). CONCLUSIONS: The result of the motion of each joint gives an insight into the biomechanics of the equine neck. The small FE ROM at C5-C6 illustrates the pathogenetical relevance of the model for the development of osteoarthritis. The calculated data also provides a source for inverse dynamics.

Activity of the equine rectus abdominis and oblique external abdominal muscles measured by surface EMG during walk and trot on the treadmill.

REASON FOR PERFORMING STUDY: The rectus abdominis (RA) and oblique external abdominal (OEA) muscles are both part of the construction of the equine trunk and thought to be essential for the function of the spine during locomotion. Although RA activity at trot has previously been investigated, the relationship between OEA and RA at walk and trot has not yet been described. OBJECTIVES: To document abdominal muscle activities during walk and trot, and test the hypothesis that muscle activity at walk would be smaller than at trot. MATERIALS AND METHODS: Six horses (8-20 years old, 450-700 kg) were used for surface electromyography (EMG) measurements, with EMG electrodes placed caudal to the sternum (RA) and at the level of the 16th rib (OEA). On all hooves, the withers and the sacrum reflective markers were placed to determine motion cycles. Normal distribution of data was tested using a Kolmogorov-Smirnov test and Student's t test was used to compare left-right and walk-trot differences (P < 0.05). RESULTS: Minimum, maximum and mean EMG values recorded at walk were significantly higher at trot than at walk in all horses for OEA and in 5/6 horses for RA. At walk, EMG activity ranged from 8-44 mV (RA) and 7-54 mV (OEA). At trot, EMG activity ranged from 18-150 mV (RA) and 27-239 mV (OEA). There were statistically significant differences between maximum activities of left and right OEA and RA muscles at walk in all horses, and in 4/6 horses at trot. CONCLUSIONS: Muscle activities of OEA and RA are smaller at walk than at trot. At walk, the OEA/RA ratio is lower than at trot. There are more significant correlations between muscle activities of both RA and OEA and limb movements at walk than at the trot.

The effects of different saddle pads on forces and pressure distribution beneath a fitting saddle.

REASON FOR PERFORMING STUDY: Saddle pads are widely used in riding sports but their influence on saddle pressures is poorly understood. OBJECTIVE: To evaluate the forces acting on the horse's back, and the eventual pressure distribution by using different saddle pads underneath a fitting saddle. METHODS: Sixteen sound horses of different breeds and ages were ridden on a treadmill at walk and sitting trot. The horses were wearing a dressage saddle with a fitting saddle tree and 4 different saddle pads (gel, leather, foam and reindeer fur) successively. For comparison, measurements were made without any saddle pad. Right forelimb motion was used to synchronise the pressure data with the stride cycles. A pressure mat was used under the saddle pad to collect the kinetic data. Maximum overall force (MOF) and the pressure distribution in longitudinal and transversal direction were calculated to identify differences between the measurements with and without saddle pads. RESULTS: A significant decrease in MOF was interpreted as improved saddle fit, and a significant increase as worsened saddle fit. Only the reindeer fur pad significantly decreased the MOF from 1005 N to 796 N at walk and from 1650 N to 1437 N at trot compared to without pad measurements. None of the saddle pads increased the MOF significantly when compared to the data without saddle pad. The pressure distribution in longitudinal and transversal direction was also improved significantly only by the reindeer fur pad at trot compared to no pad. CONCLUSION: This study demonstrated that a well chosen saddle pad can reduce the load on the horse's back and therefore improve the suitability of a fitting saddle.

A comparison of forces acting on the horse's back and the stability of the rider's seat in different positions at the trot.

The aim of the study was to compare the stability of the rider as well as the forces acting on a horse's back with different seating positions at the trot (sitting trot, rising trot and two-point seat). The same experienced rider was mounted on 10 sound horses trotting on a treadmill. The kinetic data were recorded with an electronic pressure mat, placed under a well-fitting dressage saddle with no saddle pad. The rider used three different seating positions, each for 20 s. Right forelimb motion was used to synchronise the pressure data with the stride cycles. To determine the rider's stability, the movement of the centre of pressure (COP) along the transverse (X) and longitudinal (Y) axes was calculated. The force was taken as the sum of all segments of the pressure pad multiplied by the area of the pressure pad. The maximum force and the X- and Y-deviations were evaluated using ANOVA for repeated measures with a Bonferroni Post hoc test. The stability of the rider in the Y-direction was significantly highest in the two-point seat, followed by the rising trot and the sitting trot, respectively. In the X-direction, there was no significant difference between the three positions. The significantly highest load on the horse's back was at the sitting trot (2112 N), followed by the rising trot (2056 N) and the two-point seat (1688 N). The rider was most stable in the two-point seat while transferring the lowest load on the horse's back. The rising trot was found to be more stable and less stressful for the horse's back compared to the sitting trot.

The influence of different saddle pads on force and pressure changes beneath saddles with excessively wide trees.

This study was performed to investigate the forces and pressure distribution under different saddle pads when an excessively wide saddle is used. Eighteen sound horses were ridden on a treadmill at walk and trot. The horses were equipped with a dressage saddle with an excessively wide saddle tree and four different pads (gel, leather, foam and reindeer-fur) used sequentially. For comparison, one measurement was made without a saddle pad. A pressure mat under the pad was used for the collection of kinetic data. Kinematics from the right fore-hoof were required to synchronise the data with the stride cycles. To identify any differences between measurements with and without saddle pads, the maximum overall force (MOF) and pressure distribution in longitudinal and transversal directions were calculated. The saddle pressures and MOF showed significant intra-horse effects. At walk, the foam and gel pads significantly reduced the MOF in 44.4% of cases, whereas at the trot, the gel and reindeer-fur pads significantly reduced MOF in 61.1% of subjects. The leather pad increased MOF in the highest number of horses at walk (27.8%) and trot (33.3%), although these results did not reach significance after inter-horse effects were included. The choice of a saddle pad to improve the fit of an excessively wide saddle should therefore be based on highly individual criteria for each horse.

Gait pattern of the ataxic horse compared to sedated and nonsedated horses.

REASONS FOR PERFORMING STUDY: Equine ataxia is routinely evaluated subjectively by clinicians; however, objective measurements of the movement and coordination of ataxic horses have not been reported. OBJECTIVES: To document the movement pattern of ataxic horses and compare the results to the movement of neurologically sound horses with, and without, sedation. METHODS: Seventeen ataxic horses were evaluated walking and trotting on a treadmill using a 3D high speed video system. From the horizontal movement of hoof markers the autocorrelation function (ACF) of the left forelimb and the cross correlation function (CCF) between the left forelimb and other 3 limbs (CCF foreleft/hindright [flhr], foreleft/ hindleft [flhl], foreleft/foreright [flfr]) was calculated. This resulted in a value of motion cycle consistency. The results were compared to data of 17 neurologically normal horses with, and without, sedation with detomidine. For statistical analysis the t test for independent samples was used. RESULTS: Comparing normal (NO) and ataxic (AT) horses at the walk, highly significant differences for the ACF and for all the CCFs were documented. At the trot, ACF and CCFs flhr and flfr were significantly different in the NO and AT groups. Comparing sedated and ataxic horses, only the CCF flfr at walk and at trot were significantly different. CONCLUSION AND POTENTIAL RELEVANCE: Ataxia is best documented and examined at the walk. At trot pendulum effect may make coordination easier for horses. The results of this study serve as basic data for evaluating questionably ataxic horses.