check out Gymatic featured in Apple Watch app store. Exercise classification + rep counting. I am the developer and we already have a lot of active users using the solution in Gym.
* How to track workouts where arms don't move? Add a second sensor, or create artificial arm movement.
- Want to track Leg Press? Strap phone to your leg. Or keep hands on your leg to move along.
* How to distinguish between similar workouts/add custom workouts? Custom classification per user means a smaller pool of workouts to distinguish.
- It takes just 3 seconds to train any new exercise