I’m pretty sure that the reason treadmills are used for cardiac rehab is the fine control over intensity by virtue of belt speed and incline. When I suggested we spring for a tread for home use as he was coming to the end of his rehab, husband’s response was to the effect that he could go outside to walk. Which is true…but living on the side of a mountain with every direction facing grades of 8%plus, he only had to try it the once to accept my usual adage…“You can listen to me now…or believe me later” as correct. Actually, it took two goes of venturing out, and me having to drive to pick him up for the last 200 yards or so to home.
Tangentially, the purchase was instrumental in me making the move to DIY doctoring and diagnosis too. Treads are fundamentally a pretty boring piece of equipment (as are most substitutes for the Real Thing) and one strategy for my Z2/MAF training was to listen to absorbing podcasts alongside the built in training programmes. That’s how I discovered Peter Attia’s and his guests’ podcasts. Been a worthwhile investment all round for us.