Researchers from the Hong Kong Polytechnic University and Tianjin University have unveiled a system for measuring a subject's locomotor-respiratory coupling (LRC) ratio during exercise — using wearable RFID tags.
"The locomotor-respiratory coupling (LRC) ratio of a person doing exercise is an important parameter to reflect the exercise safety and effectiveness," the team explains in the paper's abstract. "Existing approaches that can measure LRC either rely on specialized and costly devices or use heavy sensors, bringing much inconvenience to people during exercise."
"To overcome these limitations, we propose ER-Rhythm using low-cost and lightweight RFID tags attached on the human body to simultaneously extract and couple the exercise and respiration rhythm for LRC estimation."
The ER-Rhythm system places RFID tags on the arms, legs, and on the front and back of the user's chest. Two active RFID antennas are placed around the exercise area — one in front of the user, which reads the front-chest RFID tag and the limb tags, and one at the rear which reads the back-chest tag. An alternative approach uses a single antenna, with the subject placed in front of a radio-reflective wall.
By analyzing the backscattered signal, the researchers were able to track limb movement — but tracking respiration was more of a challenge. "The minute respiration movement can be overwhelmed by the large torso movement," the team states. "To address this challenge, we first leverage the unique characteristic of human respiratory mechanism to measure the chest movement while breathing, and then perform dedicated signal fusion of multiple tags interrogated by a pair of antennas to remove the torso movement effect. In addition, we take advantage of the multi-path effect of RF signals to reduce the number of needed antennas for respiration pattern extraction to save the system cost."
During testing, the ER-Rhythm system proved able to accurately estimate locomotor-respiratory coupling ratio figures between 92 and 95 percent of the time — and for a fraction of the cost and invasiveness of systems like cardiopulmonary exercise testing (CPET) equipment. The researchers note, however, that the system is presently only suited to in-place exercises which don't involve large positional changes; adjusting the system to work with other exercises, like yoga and aerobic dancing, will be the subject of future work.
The paper is available to download as a PDF following its publication in the journal Proceedings of the ACM on Interactive, Mobile, Wearable and Ubiquitous Technologies.