If I had to pick one characteristic of a successful workout, it would be… FUN. Why? Because we don’t need a lot of encouragement to keep having more fun.
Workouts work because we do them, not because they’re the most perfect one ever. I can design a workout that ensures that every muscle group gets the optimum amount of work. It might take three hours to complete and a whole gym’s worth of equipment. A few souls might try it, once, but once would be enough.
Now I’m not saying that I habitually design workouts with gaps in them or that none of us should ever do any exercise that isn’t fun (looking at you, burpees!)—I do try to balance the exercises I give to my clients and we all have to do a few burpees—but that we have to work out more than once for it to make real changes. And to make that happen, the workouts had better be fun.
Fun-adjacent workouts also work, once we’re really into the fun bit. People who love, say, biking, are willing to do some lifting if it means that they can bike better or longer or faster or with less pain.
Short version: start with what you love doing and go from there.