Abstract: Apparatus for determining the health or fitness, under an exercise load, of an animal such a horse comprises: a first sensor (incorporated in module (3) and having electrodes (5, 6)), positioned in blanket (1) under saddle (2a) of a horse, generating physiological data, e.g. breathing or heart rate, blood pressure or flow, temperature, etc; a second sensor, also incorporated in module (3), for generating position data, e.g. a GPS sensor having antenna (11). By using an algorithm, a fitness indicator such as velocity at a heart rate of 200 beats per minute (V-200) can then be derived using data from the sensors. Lameness, disease or poor physiological potential of the animal can thus be identified.