Hign intensity for higher swing speed, range of motion for flexibility
These threads really interest me as I have been very into 'fitness' and its effect on speed & strength for quite some time.
I am fairly well read in the subject (no expert by any means) and have the following opinions (based on my reading).
If you want to increase speed, you need to develop fast twitch muscle fibres. As it happens every athlete that requires quick movement in their discipline, i.e sprinting, Javelin, discus and any throwing track and field events, long drive etc have a high proportion of fast twitch fibres, we know this as various muscle biopsies comparing marothoners with sprinters show a much higher fast twitch ratio in the sprinters.
Now the only way to increase fast twitch fibres is through high intensity anerobic work i.e weightlifting. You will also find a correlation between muscle and stregnth and speed, they are all related - speed requires fast twitch muscle fibres which have the potential for the largest size when 'exersized' (hence why the above athletes are nomrally very muscular) in order generate more speed the muscles need to become larger, and therefore have the capacitiy to move things more quickly and more heavily. Basically if you want to be faster you need to get bigger muscles, and if you want bigger muscles you will need to do productive resistance training. Do the most efficient exercises for developing specific musculature required for the golf swing.
Where alot of people go wroing is in assuming the best exercises for developing speed must directly immitate the action of the skill itslef. No. You must seperate skill conditioning from physical conditioning. Do drills that help with skills if need be, but do exercises that are designed to work particluar muscles and group in the most productive manner, and that is not by necessarily imitating a swing movement, it is by doing exercises that are designed to tax the muscualture. A means to an end...
Now you may say what about the guys who are skinny and hit the ball a long way? well those guys will have a high ratio of fast twitch too, however its my view they would be even longer if they trained!
Felxibility plays a large part in being able to utilize the speed you are capable of generating and that is why it is important to engage in exercises that have a full range of motion so the muscle is being worked over its full range.
I personally work out very intensley, in order to stimulate growth in the fast twitch fibres, 20 mins a time once a week max. Lat pulldowns, dips, deadlifts, squats, shoulder presses. Age old exercises that are proven to efficiently tax the whole muscualture of the body.
I have an average driver swing speed of about 125mph maxing out at 134 when I give it some whip( according to flight scope / Tm) and Im getting faster as my training progresses. I put it down to very inetense but brief exercises.
I highly recommend the book Body by Science by Doug Mc Guff.
Sorry for any typos, at work and in a rush