Development of a New IoT Device to Acquire and Analyze Gait Information of Horses in Training

2. Materials and Methods

2.1. Equtum® trial

Equtum® was developed in collaboration with technical experts in ABEL Inc. and a team of veterinarians from Tokyo University of Agriculture and Technology. Before starting to use the system, a lithium-ion battery is set in the sensor box, and the dedicated Equtum® app downloaded to a smartphone with GPS function is started to confirm that the communication status with each sensor is normal. Each sensor is placed in the pocket of a dedicated leg protector and attached to the horse's limbs. The dedicated leg protectors can be attached and detached with Velcro tapes. When attaching, it is necessary to check the forelimb and hindlimb, the top and bottom of the sensor box, or the right and left sides, to ensure that they are correctly attached (Figure 1A and B). The heart rate monitor (Polar Equine trotters, Polar, Japan) is attached to the front of the abdominal belt (Figure 2A). The elastic, soft, optimized belt has a button to attach the heart rate sensor and a plastic buckle for easy attachment and removal. At this time, ultrasound gel is applied to maintain contact between the monitor portion of the belt and the horse (Figure 2B). When the dedicated Equtun® app on the smartphone that receives information from the sensors is launched, communication with the sensors begins immediately, and when each sensor is recognized, the "Start measuring" indicator is ready to be tapped (Figure 3). After communication with each sensor is established, the smartphone is placed in the pocket of the special saddle cloth and the horse is subjected to the training (Figure 4). When a horse equipped with the sensors trains on the training course, data such as stride, pitch, impact when the leg touches the ground, ratio of legs swinging in space (Swing time ratio, STR) [14], heart rate, etc., based on the distance traveled, speed, leg angles such as left/right or front/rear, and acceleration, as well as position information, are transferred to a server in the specialized cloud. All data is stored on a server in the cloud. The senior trainer checks these data in real time or after training using a dedicated terminal device.

2.2. Test training and data collection.

Horses used for test training were Thoroughbreds (2 geldings and 2 mares, ages 4-12 years) being retrained as retired racehorses and competition horses (2 geldings, KWPN 22 years and Westphalia 22 years). The horses are kept in good health by veterinarians, who ensure that they are free of injury, disease, pain, and lameness. After attaching sensors and tablet terminals to the horses, the test training consisted of walk, trot, canter, and gallop for an arbitrary length of time was performed to check communication and data acquisition status. The data acquired from the sensors and the wearable tablet were analyzed by a dedicated terminal tablet device. These test trainings were conducted in accordance with the guidelines for animal experiments at Tokyo University of Agriculture and Technology and were approved by the university's animal experiment committee (approval numbers R03-53, R04-86, R05-101, and R06-25).

3. Result

3.1. Waveforms of four different gait patterns of horses

Attaching the sensors on the horse was easy. The horse did not seem to be particularly concerned about the sensor, that was able to perform training exercises while wearing it without any hindrance to its mobility. The communication with the tablet terminal was good, and various data could be acquired without any problems. The differences in waveforms depending on the horse's gait acquired by the sensor are shown in Figure 5. In walk, the left and right forelimbs alternately repeat a waveform with a large amplitude, while those of the hindlimb is smaller than forelimbs. In trot, the waveforms with larger amplitudes are repeated for a shorter period of time than in walking. In canter, peak waveforms are observed not only in the forelimbs but also in the hindlimbs, and the repetition rate of the waveforms increases. In gallop, the waveform with a large amplitude is repeated, clearly different from the previous three gait patterns.

3.2. Data acquisition during test training

Figure 6 shows the screen showing the data acquired during the test training on the dedicated terminal tablet. Along with the position information, data such as distance traveled, speed, acceleration, and heart rate at that time were acquired and drawn as a line graph on the training analysis screen (Figure 6A). On the gait analysis screen, the stride, pitch, impact of the leg on the ground, and the ratio of the leg floating in space (STR) are calculated and displayed (Figure 6B), which are calculated from the angle and acceleration of the leg on the left, right or front and back. In particular, the angles of limb step and kick-up are measured and their ratios are analyzed, allowing the trainer to review the data at each time point (Figure 6B). The angles of limb step-in and kick-up are analyzed as shown in Figure 6C, using the straight standing position as the reference (0^o).　 Average degree of the step-in and kick-up angles of each limb are shown on the screen (Figure 6C).

Figure 7 shows the waveform data for the time indicated by the arrow in Figure 6A, and the gait patterns and lead forelimbs were extracted. The time course of each gait on the graph is as follows: from start to 35 seconds is trot (a), from 36 to 55 seconds is canter in the left lead (b), from 56 to 148 seconds is gallop in the left lead (c), from 149 to 175 seconds is gallop in the right lead(d), from 176 to 219 seconds is gallop in the left lead (e), then canter in the left lead (f). In the data at this time, speed was maximal in the right lead gallop, and at the same time the stride was increased. The highest heart rate (HRmax) and the speed at the highest heart rate (VHRmax) was recorded at 175 seconds in the graph. The timing for the heart rate to reach 200 beats/min (V200) was 67 seconds. The pitch tended to increase in advance of the speed and became at its highest value of the day when the max speed was recorded. The heart rate rises immediately upon entering the gallop, then remains almost flat, and then quickly declines as the speed was reduced to canter.

4. Discussion

Equtum® analyzed the gait patterns, lead leg, ground impact, and STR during training, as well as step-in and kick-up angles of each limb. Heart rate, speed, stride length, and pitch were also recorded over time. The heart rate of a racehorse at rest is about 30 to 40 beats/min, and it has been observed that horses with high racing ability have a low heart rate at rest [15]. However, no large-scale analysis has been conducted. On the other hand, when a racehorse begins to run, its heart rate gradually increases, but once it exceeds 16 meters per second, its heart rate does not increase any further. The heart rate at this point is called the maximum heart rate (HRmax). HRmax varies greatly among individuals and is known to decrease with age [16,17]. When a horse is run at various speeds, the speed at which the maximum heart rate is recorded is called VHRmax [16,17]. VHRmax has been reported to correlate with maximal oxygen uptake, which increases with training, and is considered to be an excellent index for evaluating physical fitness of each horse [15]. In addition, the index that indicates the running speed when the heart rate reaches 200 beats/min is called V200 [16,17]. On the other hand, the time point when the heart rate returns to 100 beats/min (THR100) indicates the resiliency of the heart and is an indicator of the horse's cardiopulmonary capacity. Studies have been conducted on the relationship between horse training and cardiopulmonary capacity using these indices, but no device has been developed that can simultaneously measure and analyze the exercise state of the limbs and the horse's balance, as well as heart rate. Using Equtum®, it is clear that HRmax, VHRmax, V200, and THR100 can be easily confirmed on the screen and comprehensively evaluated along with each limb condition.

Various measurement devices have been developed to analyze the heart rate and speed of racehorses and competition horses during training [18,19,20]. Most of the system uses GPS to measure both speed and heart rate of the horse at the same time. Some of these measuring devices are attached on the girth and transmit speed and heart rate data to a dedicated terminal. Riders and trainers receive data feedback for short- and long-term analysis of the horse's speed and balance during training, as well as changes in the horse's movement due to the rider's ride. Data is visualized using a dedicated app installed on a tablet device. In contrast, Equtum® is a system that measures positional information, speed, and heart rate, along with various information from each limb, for a comprehensive evaluation of the horse's movement. Moreover, on the gait analysis screen, data of the impact, STR, and step-in/kick-up angles of each limb help trainer to know the horse's left/right or front/rear balance, and dominant lead legs. This equipment can be used not only for training, but also for veterinary purposes such as rehabilitating injured horses and determining the effectiveness of treatment.

In the horse training, particularly in training of racehorses, experience and senses of the trainer have been highly important, but it has not been difficult to quantify and visualize. Equtum®, the IoT device exclusively used in horse training, is a device that enables decision-making based on numerical values by providing real-time data such as speed, stride, and heart rate, etc. In addition, by inferring the distance aptitude and fatigue level of the relevant horse based on past training and race results, more accurate evaluations of training time, intensity, and training intervals can be made. Furthermore, in cooperation with veterinarians, it will be effective in predicting and early detection of pain and/or injuries of horses. We believe that the use of this system will contribute to a future in which all racehorses and competition horses can safely perform at their best.