How is Locomotion Measured?
Mathematical and physical models are useful in describing and testing equine locomotion. Below, a few techniques that have been developed and utilized due to technological advancements are described.
Equine hoof mounted accelerometers
Figure 1. Hoof Mounted Accelerometer. Picture of hoof-mounted accelerometer and telemetry unit in a elasticated exercise bandage. The unit is mounted at the thrid metacarpal bone. Adapted from (Witte et al. 2006)
Foot mounted accelerometers can be used to determine timings of footfall, both foot-on and foot-off (Fig. 1). These values can then be used to determine footfall intervals, ground reaction force and stride timing variables such as stance time, protraction time, and stride time. The output signals from foot-mounted accelerometers are logged by various methods. Telemetry of analogue signals into computers is one of the main methods used in the past (Kai et al. 2000). These systems however can result in data recording errors. One type of interference is signal interference and re-radiating radio modulation. Other errors include shielding effects of the subject which reduce the range of the units and voltage proportional to the acceleration through the stride. Difficulty in wire attachments and interference with normal locomotion are also common problems associated with these methods. All equipment used must tolerate high accelerations. Parsons has used MP3 recorders to provide relatively cheap, robust, reliable and accurate logging systems. In his study, MP3 recorders were successfully synchronized and combined with an accelerometer and external battery for the measurement of stride timings in equine gait (Parson and Wilson 2006).
Cinematography
High-speed cinematography has shown repeatability in studies. Reference markers relative to the test are placed on the horse. Usually the markers are dots glued right to the skin. Gates of known dimensions or other landscape reference points are used to determine a scale for measurements. Filming is performed on both sides of the horses, always from a constant distance. This film is then analyzed with a point digitizing system and coordinated with an electronic frame counter. Measurements such as anatomical distances, protraction, retraction and hoof contact are some of the data that can be determined by this method (Kobluk et al. 1989).
Treadmill
Horses run on high speed treadmills allow for velocity and elevation to be controlled. (Back et al. 1995a) However, the horse may not exhibit its’ normal stride pattern in this unnatural environment. A treadmill can be combined with cinematography or hoof mounted accelerometers to collect data.
GPS receiver
A GPS receiver attached to either the horse or rider in saddled horses allows for distance measurements to be made easily. Time collected in co-ordinance with distance allows for speed calculations to be made and measured (Robilliard et al. 2006).