My suggestion is, like reality, when a rider is on a climb and drops below, say, 5 or 6 MPH, a button will pop up that says “walk bike”. When pressed, the avatar dismounts the bike starts to walk, while holding the bike. The resistance goes to -2% or -3% grade. This allows the biker to keep moving “walking” while recovering. The app will not allow the walker to exceed 4 or 5 MPH. There will be a button that will read “back on the bike” and this will transition the rider back on the bike and back to “normal” riding.