Energy expenditure is an important parameter in the assessment of gait and orthotic treatment of heavily handicapped patients, since any orthosis which increases the effort required is likely to be discarded with consequently disturbing implications. Heart rate has been shown to be a reliable monitor of energy expenditure and is convenient because ECG can be telemetered by a miniature radio transmitter, Using a transmitter causes minimal interference with the patient, but care must be employed to obtain ECG signals free of artefact from subjects who are exercising. Means of reducing artefact are discussed, as we ways in which heart rate monitoring by radio telemetry is being used in the routine assessment of orthotic treatment of paediatric patients and the development of new orthotic devices.