Abstract :
[en] History
Equine exercise physiology development would have been impossible without the use of High-Speed Treadmills (HST), which use arose in the 1960s and increased dramatically in the following decades. High Speed Treadmills were initially employed in a vast array of research protocols focusing on cardiovascular, respiratory, biomechanical, musculoskeletal, thermoregulatory, and training adaptations of the equine organism in response to exercise. Thanks to the creation of this body of knowledge, HST have been then used for diagnostic purposes to investigate potential causes of poor performance in equine athletes. Nowadays, although remaining essential in research protocols, clinical application of HST has decreased, as they are being progressively replaced by different portable and wearable diagnostic devices allowing measurement of different locomotor, cardio-vascular and respiratory parameters. Technological progress in veterinary medicine has resulted in more user-friendly and on- field applicable use of diagnostic techniques. These devices provide continuous, real-time data during training sessions and competitions, thus allowing trainer, jockeys and riders to follow the training charge and progression of their horses day by day.
Cardio-vascular parameters assessment
Resting and exercise heart rate (HR), heart rate variability (HRV) measurement and electrocardiography (ECG) are essential tools to assess and monitor the horse’s response to exercise, conditioning, recovery, overtraining risk as well as to detect pathological arrythmias that could interfere with performance. Early ECG systems were not able to display HR in real time, extraneous electrical noises were commonly disturbing the transmission, data were printed on paper and HR was hand-calculated. Newer wearable HR and ECG telemetry systems have overcome many of the difficulties of the earlier devices. Moreover, most of these systems allow live transmission of HR and ECG, and, when coupled to a global positioning system (GPS) or to an inertial measurement unit (IMU), the analysis of cardiac values in correlation with other parameters such as speed and blood lactate concentration. Data can be stored on cloud-servers with the generation of digital reports for more detailed analysis.
Upper airway examination
Fibro-endoscopes have been the basis of equine airway visual assessment for decades before the introduction of video-endoscopes allowing a better quality of image. The combination of digital endoscopic systems with the use of HST for in situ exercise tests allowed veterinarians to visualize upper airway behavior of horses during trot, canter or gallop. Nonetheless, during these types of tests, the horse was generally held by a halter, a rope and by a person standing at the side of the horse, leaving its head in a quite neutral position and without the possibility of reaching specific race speeds. The introduction of portable overground endoscopy has been revolutionary as it has allowed the understanding of the evolution of common (resting) upper airway endoscopy obstructive problems in equine athletes during exercise, thus finetuning the diagnosis of airway pathologies, their surgical correction and the objectivation of surgical outcomes. Portable video-endoscopy has also documented some dynamic conditions which manifest only during strenuous exercise, such as displacement of the soft palate, epiglottic entrapment or retroversion. Furthermore, the use of overground endoscopy devices on the field has permitted to take into account the intervention of the rider (by poll flexion, tightening of the reins, execution of certain movements) on upper airway diameter and compliance during exercise. Effectively, rider’s effect has been shown to significantly impact ventilatory dynamics and even animal welfare.
Assessment of aerobic capacity
Determination of maximal oxygen consumption (VO2max) is the one of the most commonly used tests to assess aerobic and thus athletic capacity in human athletes. In equine medicine, VO2max has been shown to be correlated with speed in Thoroughbreds and also in Standardbreds, a high aerobic capacity was found to be a major contributor to a faster racing performance. Assessment of VO2max requires measurement of air flow rates, of O2 and CO2 in expired respiratory gas by the use of ergospirometers. However, there is limited commercially available equipment suitable for the high flow and respiratory rates of horses during exercise, especially on the field. Although some overground ergospirometers have been developed for field conditions, the system itself may impair ventilation and prevent horses from reaching maximal exertion. A recent study described the design and validation of a facemask with the potential to allow an accurate breath-by-breath measurement of airflow and VO2max on the field with promising results.
Assessment of anaerobic capacity
Anaerobic capacity is estimated from peak postexercise blood lactate concentration, however, this concept is controversial, as post-exercise lactate is affected by different parameters such as sampling time, individual variability in monocarboxylate transporters, fitness level and type of exercise test. Different methods have been described to estimate the anaerobic power; in particular, the maximal accumulated oxygen deficit (MAO-DALT) method has been measured in horses, calculating the sum of the lactic and alactic metabolism contribution. This method can be used in a field setting where exercise intensity is generally unknown.
Speed calculation
Speed (or velocity), together with the covered distance, are crucial parameters when measuring workload in athletic disciplines. The integration of GPS to portable devices together with heart rate monitors has allowed the determination of traditional fitness parameters such as HRmax, VHRmax, V180 and V200, enabling measurement of the response to training, detection of poor performance and even the early identification of horses with limited earnings, thus helping trainers in taking decisions about the racing career of their horses. Nonetheless, the use of speed values in warmbloods and in indoor arenas remains more challenging and standardization of tests more difficult to reach.
Locomotor evaluation
Lameness is defined as an alteration of the normal gait, caused by structural or functional musculoskeletal disorders. Ancillary tests used to examine a lame horse include inspection and palpation of limbs, evaluation of the horse at rest, at different gaits and on different surfaces in order to visually assess asymmetry in the vertical displacement of head or pelvis. Nonetheless, some studies have shown that subjective evaluation is not always reliable when lameness is mild to moderate, especially in hindlimbs. Objective gait analysis (OGA) provides valuable information about the kinematics in sound and lame horses, by the use of body-mounted sensors called inertial measurement units (IMUs) consisting of an accelerometer, a gyroscope and a magnetometer, with or without integration of a GPS device. There is increasing body of evidence that IMU-based methods can not only monitor and quantify horses’ kinematics, thus helping in lameness investigation, but also objectivate the horse-rider interaction, the influence of some sedatives, the efficacy of corrective shoeing, treatments and/or of rehabilitation techniques. Other kinematic analysis techniques consist in 3D optical motion capture (OMC) systems, which are well-validated, accurate and precise, but restricted to indoor use, to high-caseload veterinary practices or to research contexts due to their higher cost and lower versatility compared to IMUs.
Metabolism and energy assessment
Assessing metabolic adaptations occurring in response to exercise has been done in the past using calorimetry, blood analyses, muscle tissue analysis and isotropic tracers. Nonetheless, measuring blood-borne metabolites provides only a partial view on metabolic interactions. Indeed, blood remains a “crossing point” where organs release, take up and exchange substrates, giving limited information on rates of production and utilization of metabolites. The recent integration of ‘omics’ (proteomics, metabolomics, transcriptomic approaches) to equine research on metabolism should allow a better understanding on its regulatory mechanisms. More recently, High-Resolution Respirometry (HRR) has been employed to assess mitochondrial function in healthy horses, to determine the effect of conditioning and the effect of some muscle pathologies (as PSSM and MA) and of exercise-induced hyperthermia.
Data integration
One of the most exciting developments is the integration of these monitoring tools into centralized platforms powered by artificial intelligence (AI). These platforms collect data from various devices, such as heart rate monitors, GPS trackers, and motion sensors, and analyze them to provide trainers with insights and predictions. AI algorithms can help in detecting subtle changes in a horse’s performance or physiology that may indicate fatigue, stress, or early signs of injury, allowing for proactive adjustments in training regimens, thus shifting the role of the veterinarian from a curative to a more preventive medicine.
Overtraining and exercise-induced alteration of immunity: promising research fields
The effect of exercise and conditioning on immune parameters and the existence and objectivation of an “overtraining syndrome” are topics of interest in human sports medicine. In equine medicine, this research field remains overlooked but sparks interest among researchers. It is widely recognized that moderate regular exercise has a beneficial effect on the immune system while strenuous exercise can have a immunosuppressive effect. In particular, in the 24h following an intense and/or prolonged physical activity, human and equine athletes experience a higher susceptibility to respiratory infections (“open window period”). An increase in physical workload should be followed by a proper recovery phase, otherwise the non-respect of this mandatory period can create an overtraining syndrome. The assessment of immune function is difficult because local and systemic immunity may react differently to a stressor such as exercise. Likewise, the diagnosis of overtraining remains challenging in horses, being generally based on local and systemic parameters, blood values and behavioral reactions, even if a unique and reliable overtraining biomarker has not been recognized to date.
