**2. MedBike system overview**

Numerous designs for instrumented bikes have been proposed in the literature and in industry; additionally, a number of patents have also been awarded. The closest to our system, in which a VR controllable resistance system was developed for a cardio fitness application was proposed in [25, 26]. Commercial virtual reality cycling systems that use VR and instrumented bicycles have appeared on the market. The Italian company Widerun [27] offers clients to connect a normal bike to their resistance device, put on a VR headset, and cycle across a virtual terrain representing world-class cycling circuits. Their system can provide variable resistance based on the in-game environment. The overall visual quality is good but is not equal to the image quality produced by Unity 3D game engine. Their system uses a Head Mounted Displays (HMD) for immersion but as demonstrated in our lab, HMD are highly disorientating which may result in falls. Their system also does not provide free steering/breaking capabilities. The American company Zwift [28] is the one that closely resembles the VR aspects of MedBike. Contrary to our system, Zwift's worlds are static and not very engaging and cannot be modified easily for gamification. Zwift's graphics rendering suffers from many visual anomalies like aliasing and poor level of details via pop-up. Most of these commercial systems target the pro-cycling niche market focusing mainly on exercise performance and training, not medical applications. Most are them are dedicated cycling systems and cannot be easily modified for gamification. None of these systems offers patient sensor-based telemonitoring.

Following numerous discussions with CR clinicians, we came up with design specifications for the system that are as follows:

	- Real-time access to patient's vital signs, current power produced, cadence, etc.;
	- Access to data from previous MedBike sessions, including from player sessions (sessions completed individually without clinician);
	- Patient's medical records;
	- Secure video conferencing with each patient;
	- Ability to specify exercise parameters such as target power and cadence ranges that must be achieved;
	- Ability to record medical notes and performance of the patient during a session.
