[DrPhish]

I had a spreadsheet set up much like that in the past: it would bubble up the exercises I'd done the longest ago for a particular muscle group so I'd always get variety. It worked pretty good, but I found myself often avoiding unpleasant exercises when given choices and eventually the whole arrangement fell apart due to too many moving pieces. I also didn't see the kind of extra benefit that I thought I'd gain from performing so many variations. I also used to set up fully scheduled on/off timers for specific exercises in an app, but found that any interruption would throw the whole thing off, annoying me to no end. However, your last point was also my biggest enemy. If I get distracted online for long enough to cool down to the point that I'm worried about injury, the whole session tends to just blow straight out. That's the main driver I had for putting the simple timer in the footer: keep my device on one screen from beginning to end!