When you’re doing press ups, you’re working  many muscle groups from the chest, shoulders and arms. The main arm muscle trained is the tricep so you could balance a little by working your biceps.

I’ve never comes across someone saying that you need to work your lower back muscles when doing sit ups. Most people do sit ups incorrectly so they are actually working their lower back muscles more than their abs.

As with all exercise, you need to discuss training with qualified trainers to make sure you get a sport specific, balance program. The difficulty here is that not many trainers understand the requirements of a badminton player in order to provide the right program.

Paul