To collect vital data from a group of outdoor exercisers in real-time and reliably, we propose a wireless multihop network system based on a flooding/time division multiple access (TDMA) protocol with an extended superframe structure. For wireless vital sensor nodes (VSNs) put to the bodies of exercisers, the system first randomly and temporarily divides a whole group of VSNs into several subgroups and assigns a distinct superframe to each subgroup. Then, when VSNs move around in a ground, the system adaptively changes subgroup members so as to make them uniformly and widely spread in the ground by using the location information on all the VSNs.In this paper, we evaluate the performance of the system by an experiment. We conduct the experiment in an outdoor ground of 60m×90m for 45 min, involving 50 subjects, where we put VSNs to 18 subjects out of them. We show in the performance evaluation that the system can collect vital data from the 18 subjects even when all the subjects perform a variety of exercises, once in 2 sec in average, for 45 min regularly, and in 94.9 % data collection rate reliably.