Use of Global Positioning Systems (GPS) in data acquisition for equine exercise physiology

Studies of physiological responses to exercise in the horse frequently describe the relationships between measured variables, such as heart rate and oxygen consumption measured against velocity of the animal. Treadmill laboratory facilities allow accurate control and measurement of the velocity of exercise. However, studies made on the track or in the field more accurately describe the true physiological and metabolic demands of exercise. This is because field studies account for factors such as rider weight, gait differences, ground surface differences and acceleration. For field studies to be effective, an accurate technique of recording horse velocity unimpeded by bulky equipment is required. This paper discusses the use of an animal mounted GPS receiver. GPS derived time stepped velocity and altitude change can give a true measure of work output. When simultaneously recorded with other ambulatory physiological instrumentation, the GPS forms the core of a versatile data logging solution. Presented is an overview of the NAVSTAR Global Positioning System, discussing factors affecting resolution, accuracy and use of Differential mode GPS (DGPS), with a view to optimising physiological measurements. Interfacing to a data logger is discussed, together with applications of GPS synchronised time marks.