I like that you interviewed people with a wide variety of fitness habits! I tried to interview 3 people with roughly similar backgrounds to see if they all felt the same, but I think interviewing 3 very different people produced equally interesting responses.
I wish I could think of a better way to measure exercise intensity than visible sweat — I think that’s a tough measurement because some people sweat more than others or in different places, but I’m not sure what a better option would be. Maybe how hard they are breathing? (Or if you could use instruments, how fast their heart is breathing?)
What if we answered your product statements with a game activity product? I think bubble soccer is brilliant, and I wonder if we could come up with an equally simple accessory to gamified exercise.