Weight training records feature
It would be useful for the weight training activity type to have an entry option for tracking the actual workout routine.
lift - weight - sets X reps per set.
Squat - 225lbs - 5 x 5
Pushups - bodyweight - 2 x 25
Analytics could be programmed in to approximate calories burned per type of motion, suffer score, tracking of performance on each type of exercise over time, PRs, etc.
Currently, I just write down my workout plan and take a photo of it to attach to the activity, and that's how I'm keeping track of weight training progress.