Rider Equine Biomechanics: A Case Study

Q4E Case Study 40 – Rider Equine Biomechanics: A Case Study

Background:

The rider, a 35 year old female who has been riding for approximately 8 years, has stated that she is currently suffering from back pain and is undergoing physiotherapy treatment in an attempt to alleviate this pain. Her physiotherapist has suggested the back pain she is suffering from may be due to her riding technique, and that this should be examined further.

Protocol:

Two Quintic High-Speed USB3 4MPixel Cameras were used to record both the rider and the horse; these were positioned to the rear (posteriorly), and side of both the horse and rider (Figure 1).

Figure 1. The rear (posterior) and side view camera positions

Both cameras were synchronised and recorded at 300 frames per second. Semi-spherical retro-reflective markers (22mm) were attached to both the rider and horse; the location of these markers is displayed in Figure 1. In order for the markers on the rider and horse to reflect, the Quintic High Performance Bar Light was placed behind each camera during filming. The rider was asked to complete 5 trials where the walking stride for the right side of the rider and horse was evident in the side camera view; the same process was completed for the left side of the rider and horse.

Figure 2. A diagram showing the set-up for the case study. A 2 metre wide, 20 metre long channel of cones was created to ensure the horse’s path was straight and consistent. The stride analysed was taken at the middle of the channel, 10 metres from both the rear and side view camera. The Quintic High Performance Bar light was placed on a tripod directly behind the camera’s to ensure optimal reflection of the markers.

Upon the completion of data collection, the recorded trials were automatically digitised for one stride length within the Quintic Biomechanics software. The individual x and y digitised coordinates were individually smoothed in the Quintic Biomechanics software using a Butterworth Filter. The filter values ranged between 20 – 56Hz; these values were found to reduce the noise in the position of the coordinates without adding systematic error.

The independent variables were then analysed using the Quintic Multi-Trial Angular Analysis function within the Quintic Biomechanics software. This function allowed multiple trials to be analysed together with the implementation of averages and confidence intervals for the multiple trials all of the way through the stride length. The individual trials were synchronised to a common time event for the stride within the software.

Results:

Rear View:

Analysis of the rider’s position indicated a bias to the left-hand side of the horse (See Figure 3).

Figure 3. The position of the rider on the horse.
It is evident that the rider is positioned further to the left.

Further analysis found that the horse’s hip angle relative to the horizontal showed an asymmetry during the stride, tilting further to the left (Figure 4a). However, this asymmetry was not evident for the rider’s hip angle throughout the stride (Figure 4b).

Figure 4(a). The horse’s hip angle relative to the horizontal and (b) the rider’s hip angle relative to the horizontal. The bold red trace represents the average across 5 trials. The two faint red traces represent the upper and lower 95% confidence intervals, respectively, for five trials. Values greater and less than 180° indicate the hip is tilting to the left and right, respectively. The initial vertical dashed line indicates left hind heel contact. The five corresponding blue vertical lines indicate left fore contact, right hind contact, right fore contact, second left heel contact and second left fore contact, respectively.

Figure 4c. Illustration of the angles measured in Figure 4a and 4b.

The spine angle of the rider is illustrated in Figure 5. It is evident that the lower spine angle remains relatively neutral during the gait cycle (Figure 5a). However, the upper spine displayed a tendency to tilt to the left (Figure 5b); this was also apparent in Figure 5c, which displays the lateral flexion of the upper spine to the left, relative to the lower spine.

Figure 5. (a) The rider’s lower spine angle relative to the vertical, (b) the rider’s upper spine angle relative to the vertical, and (c) the rider’s upper spine angle relative to the lower spine. The bold red trace represents the average across 5 trials. The two faint red traces represent the upper and lower 95% confidence intervals, respectively, for the five trials. For Figures a and b, values greater and less than 180° indicate the spine is tilting to the right and left of the vertical, respectively. For Figure c, values greater and less than 180° indicate the upper spine is tilting to the right and left, respectively, relative to the lower spine. The time events represented by the dashed and full blue vertical lines are described in Figure 4

Figure 5d. Illustration of the angles measured in Figure 5a, 5b and 5c.

Side View:

Figure 6. (a) The rider’s lower spine angle relative to the vertical, (b) the rider’s upper spine angle relative to the vertical, and (c) the rider’s upper spine angle relative to the lower spine. The bold red trace represents the average across 10 trials (right and left side). The two faint red traces represent the upper and lower 95% confidence intervals, respectively, for the 10 trials. For Figures a and b, values greater and less than 180° indicate the spine is tilting towards and away from the direction of the stride, relative to the vertical. For Figure c, values less and greater than 180° indicate the upper spine is tilting towards and away from the direction of the stride, respectively, relative to the lower spine. The initial vertical dashed line indicates left hind heel contact. The three corresponding blue vertical lines indicate left fore contact, right hind contact and right fore contact, respectively.

Figure 6d. Illustration of the angles measured in Figure 6a, 6b and 6c.

It is apparent from Figure 6 that the lower and upper spine tilt away and then towards the direction of the stride during the gait cycle. Therefore, this suggests that the upper spine is in a constant state of flexion relative to the lower spine; this is evident from Figure 6c. It is also evident from Figure 6 that both the lower and upper spine’s angle relative to the vertical display a large amount of variation during the gait cycle.

Discussion:

Asymmetries in the motion of the horse’s hip angle and the rider’s spine angle during the gait cycle were found: there was a tendency for the horse’s hip angle to tilt to the left (Figure 4a) and the rider’s upper spine to laterally flex to the left (Figure 5c), causing the upper spine to tilt to the left, relative to the vertical, during the gait cycle (Figure 5b). It is likely these asymmetries will have a detrimental effect for both the horse and rider. The tilting of the horse to the left will place greater demands on this side of the body and over time may cause injury and potential lameness. The tilting of the rider’s upper spine to the left may also cause damage to the rider’s spinal column, in particular the lower thorax and upper lumbar region where this lateral flexion occurs. It is suggested that these asymmetries evident from the rear camera view are at least partially cause by the incorrect position assumed by the rider on the horse (Figure 3).

The flexion and extension of the rider’s spine, recorded using the side camera view, showed the lower and upper spine in predominant states of hyperextension and flexion, during the gait cycle (Figure 6). It is likely this difference between the upper and lower spine was caused by a flexion of the spinal column around the lower thoracic and upper lumbar regions. This flexion of the mid-spine region may over time again cause damage to this area. The rate of change of the spine’s flexion and extension is also evident in Figure 6; this change, and the velocity at which it occurs, may also be a cause of any current or potential spinal injuries.

Conclusions & Recommendations:

It is likely the current back pain suffered by the rider is being caused by the lateral flexion of the spine to the left, and the constant flexion of the mid-spine during the gait cycle. The constant change in the angle of the back (its flexion and extension angle), may also be a cause for this pain.

It is suggested that the position of the rider on the horse is corrected; it is likely this will reduce the asymmetries displayed by both the horse and rider. It is also suggested that the lower and upper spine angles should be positioned in a more vertical position during the gait cycle; therefore, alleviating the flexion of the mid-spine region. It is further recommended that the rider undertakes a strength and conditioning programme that is designed to improve her back and abdomen region (the core), as this should reduce the velocity at which the back flexes and extends.