Abstract: The muscle efficiency of a subject is evaluated with apparatus comprising a nuclear magnetic resonance (NMR) analytical device which comprises a hollow electromagnet having a bore of sufficient size to receive the subject. Any type of animal can be evaluated, in a preferred embodiment a horse or a human is analyzed. A treadmill within the bore and beneath the subject is utilized to produce locmotion of the subject at different rates of work. The NMR analytical device is used to measure at different rates of work the following ratio within a locomotion-producing muscle mass of the subject:Pi/PCrwhere Pi is the concentration within the muscle mass of inorganic phosphate and PCr is the concentration within the muscle mass of phosphocreatine. Methods and apparatus are provided for relating the measured Pi/PCr values to the rates of work then being performed by the subject to provide an efficiency profile for the muscle mass.

Abstract: The muscle efficiency of a living animal is evaluated with apparatus comprising a nuclear magnetic resonance (NMR) analytical device that comprises a hollow electromagnet having a bore of sufficient size to receive the animal. A treadmill within the bore and beneath the animal is utilized to produce locomotion of the animal at different rates of work. The NMR analytical device is used to measure at different rates of work the following ratio within a locomotion-producing muscle mass of the animal: ##EQU1## where Pi is the concentration within the muscle mass of inorganic phosphate and PCr is the concentration within the muscle mass of phosphocreatine. Means is provided for relating the measured ##EQU2## values to the rates of work then being performed by the animal to provide an efficiency profile for the muscle mass.