Abstract: In this paper, we present an exergame called VNM (Virtual Network Marathon). The VNM employs specially devised treadmills for running in an immersive virtual environment on a local area network or the Internet. The treadmills have various sensors embedded within them for collecting body performance data. These treadmills are then connected with computers or Set-Top-Boxes (STBs) to synchronously control the player's avatar in a virtual game environment. VNM is implemented on a novel ISCAL (Immersion, Scientificalness, Competitiveness, Adaptability and Learning) model for exergame design. The exercise time and intensity strictly conform to the physical exercise guidelines of the ACSM (American College of Sports Medicine), and a novel demonstration-based non-player modeling technique is employed to simulate a marathon race. The VNM also allows players to learn Chinese culture and obtain knowledge of the Olympics while in tour mode during or after the running exercise. We conducted a pilot study to evaluate the usability of the features of the VNM that we have developed, and with promising results.