If you already have mastered the golf swing, but get tired on the second nine holes and your game falls apart, you would benefit from a cardiovascular workout program designed to increase your endurance. Tired muscles move more slowly and they also don't have as much coordination.
If you are sore and stiff after a round of eighteen holes, then your muscles probably don't perform golf swing motions on a regular basis. The simplest conditioning program for this is to practice more. Not only will you improve your game, but the muscles used in golf will always stay loose.
You might have flexibility issues, and your shoulders just can't do that 90-degree shoulder turn or your wrists don't hinge enough to give you lots of leverage. Here is where you look into the specific stretch routines to increase flexibility. Develop a daily ritual of stretching your back, wrists, arms and hips to be the golfer you want to be.
Strength training can be especially helpful if you have a problem keeping your left leg stationary throughout the swing. Squats can build your quadriceps to help give you better form and add power to your swing.
All golfers must continually work to maintain their level of mental conditioning. Mental conditioning comes from experience. Golf is the quintessential mental sport and you must learn to control your nerves. Concentrate on mental pre-shot routines that will work best to help you focus on your shot.