It does of course involve postural / "slow twitch" strength, as opposed to "fast twitch" strength. Slow, smooth, toning exercises will be beneficial. All over toning and endurance-related exercise (sculling was very beneficial to me, overall) will help with the breathing and concentration. Isometrics may help as well.

Exercises focused on burst strength are less likely to beneficial.

For the very best results, a timer or remote release is advisable; finger impulse to the shutter button is never beneficial... unless of course you want blur...