One of the most effective ways to increase your golf swing speed and power is to use a training club. You can't get anymore golf specific than using a golf training club.
There are many golf training clubs on the market, and new ones coming out every year; but the one I'm talking about is a weighted golf training club. When you can literally mimic your athletic movement with resistance, you stand to make the biggest improvement, and make it quickly.
The goal of most strength coaches and trainers is to come up with exercises that closely resemble that particular athletic movement, but with some form of resistance. It could be handweights, medicine balls, tubing, or a stability ball.
The direct impact on a golfers swing using a golf training club is an almost immediate increase in driving distance. This is because you are training your golf muscles during the movement, through the same (or even bigger) range of motion, with many repetitions.
A secondary benefit of using a golf training club that's weighted is promoting an increase in backswing and follow through range of motion. This equates in more power at impact. Golfers are always trying to find ways to improve golf flexibility and power; and this is one great way to do it.
Though using a golf training club won't be the cure to all your physical ailments and limitations, but it will give you a head start on swinging with higher clubhead speed.
Just think about it! Swinging a golf training club won't improve hamstring flexibility, nor will it strengthen your lower back. There are many specific areas of the body that don't get worked when swinging a golf training club.
This is where you would do specific golf exercises, stretches and drills to isolate those weak areas to greatly improve your overall golf performance and prevent future injuries.
Another benefit of a golf training club that's weighted is a quick warm up before you hit balls at the range or even play. Swinging it 20-30 times will quickly get your golf muscles prepared to hit balls more effectively.
Just beware! When you swing it before practicing or playing, you've got to swing your regular clubs, and hit balls with them, to make sure your sequence of motion is correct, before you hit the course.
As you can see, there are many benefits of using a golf training club; so go out and get one. They are a great training aid as part of your "off-season" training program.