Unfortunately Health will only sync data recorded on your iPhone or Apple Watch.
This is because Apple doesn't currently support Health for the iPad, and Health only syncs workouts that are completed on a "Health-friendly" device.
If you would like to save your workouts to Health, the best way to do this is to work out using your phone. Otherwise, you can work around this by manually recording workouts completed on your iPad in the Health app on your iPhone. To do this, you can go to Health > Workouts > Add Data > Add your workout here.