Several studies have evaluated the accuracy of portable metabolic gas analysis systems, which measure physical activity energy expenditure. Since the Cosmed K2 telemetric system, two K4 devices (RQ and b2) have been developed.
Physical activity energy expenditure measured using a portable telemetric device in comparison with a mass spectrometer / Maiolo, C; Melchiorri, Giovanni; Iacopino, Leonardo; Masala, Salvatore; DE LORENZO, Antonino. - In: BRITISH JOURNAL OF SPORTS MEDICINE. - ISSN 0306-3674. - 37:5(2003).