thats bull man IMHO your not goin to lose any strength on doing some warmup exercises....especially for pressing movements...you take a 10 pound wieght in oyur hand tuck your elbow in to your body and rotate that wieght with your arm at 90 degrees for like 30 seconds then you put your upper arm parallel to the floor and make a 90 degree bend up with your forearm and rotate that wieght from upright to the floor like it will fall unless you stop it...do that with both arms each of them for like 20-30 secs before any pressing movement at least and it should help warmup that shoulder...