As has been mentioned, but I'll rephrase it. No matter how good of condition you are in, shooting uses different muscles. You need to develop those muscles. Going to the range isn't enough. In the past, target shooters suggested dry firing practice, but also hanging a camera or something similar on the gun to increase the weight you are holding. This helps develop those muscles used for shooting.
Dry fire practice and 22 rimfire pistol shooting are excellent ways to increase your general pistol shooting ability.