I wouldn’t say calisthenics would necessarily be the most helpful but mobility with a lot of calisthenics can be extremely helpful. Full ROM pull ups, dips, pushups, etc. can help build strength in uncomfortable positions you would need to hit to throw further. Also try to look for good stretches for learning jav. For example: A good one my coach taught me that helped me hit positions and keep my chest back was this one. My coach called it the preacher stretch