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A four-channel frequency-modulation radio-telemetry system for the measurement of two electrocardiograms (EKGs), respiration rate, and pulmonary ventilation of human subjects during vigorous exercise is described. From the measurement of pulmonary ventilation, the oxygen uptake (and thus energy expenditure) was predicted. This is the first time (to the author's knowledge) that oxygen consumption has been predicted by telemetry of pulmonary ventilation for such sports as squash, handball, and track. The transmitter uses pulse-duration modulation. It has a range of approximately 100 meters, which may be extended by using a whip antenna. Linearity of the system is 2 percent or better from a best straight line, and baseline drift is less than 1 percent at 25Â°C. The telemetry transmitter weighs approximately 100 grams and is contained in two boxes measuring 5 by 5 by 1.25 cm. Construction of this system is considerably simplified through extensive use of integrated circuits. A complete transmitter costs about $50 (for components only) and dissipates approximately 60 mW. The batteries used provide a continuous life of 125 hours. The system has been used to obtain data from persons participating in squash, handball, track, and tennis. It may be used for many other physical activities.