Off-the-shelf wireless sensing devices open up interesting perspectives for biomedical monitoring. Yet because of their limited processing and transmission capacities most applications considered to date imply either indoor real-time data streaming, or ambulatory data recording. In this paper we investigate the possibility of using disruption-tolerant wireless sensors to monitor the biomedical parameters of athletes during outdoor sports events. We focus on a scenario we believe to be a most challenging one: the ECG monitoring of runners during a marathon race, using off-the shelf sensing devices and a limited number of base stations deployed along the marathon route. Field experiments conducted during intra-campus sports events show that such a scenario is indeed viable, although special attention must be paid to supporting episodic, low-rate transmissions between sensors carried by runners and roadside base stations.