Long-term accurate measurements of core body temperature are essential to study human thermoregulation in ambulatory settings and during exercise, but they are traditionally carried out using highly-invasive techniques. To enable a continuous unobtrusive monitoring of core body temperature on ambulatory patients and exercising athletes, we have designed a wireless wearable system that measures the tympanic temperature inside the ear, as well as skin and environmental temperature, and that allows remote monitoring of the collected measurements. In this paper, we describe the design and implementation of the system and show that it can be used to identify the circadian rhythms of core body temperature, as well as to detect the variation in core body temperature due to prolonged physical exertion. We further describe the lessons learnt during a pilot deployment of our telemetric system on several athletes during the 5 th  Lubeck Marathon, and discuss the impact of environmental parameters such as temperature and wind on the accuracy and meaningfulness of the measured values.
['Carlo Alberto Boano', 'Matteo Lasagni', 'Kay Römer']
Non-invasive measurement of core body temperature in Marathon runners