Why not allow users to add/remove their own exercises? They choose a name, and data they'd like to track for that exercise, such as distance, time, weight, reps. For example, they click Add Exercise, enter Squats as the name, and check the boxes for weight, and reps. Now, after their workout, they just click the Squats button under My Exercises, and enter the reps and weight they did for that day.
