When you read some of the older books on instruction and technique, you will notice there was a lot of focus on the lower body. The powerful driving of the legs both laterally and rotationally to produce power.
The end result of this approach was undo stress on the lower back due to the reverse C it caused in the finish. Just look at the old pictures of the golfers in their finished position and youll see the bowing of the body away from the target.
Because the golfers didnt believe in conditioning their bodies, the injuries to their lower backs was on the high end. Many of them played with back injuries. It actually shortened the careers of many of them.
Look at todays senior players. They are playing well into their 60s and even early 70s at a very competitive level. Why? Because most of them have a modern golf swing and have prepared their bodys physically to withstand the tremendous amount of pressure the golf swing puts on it.
The modern golf swing is a much more rotational movement, that is stacked at impact, not the reverse C I mentioned above.
What I mean by stacked is at impact it almost looks like the golfer is right over the ball with his/her entire body. The hips are rotated towards the target; but in sequence with the core and upper body. There is very little lateral movement of the lower body and even upper body.
This powerful rotation creates maximum torque in your core area producing much higher clubhead speed and distance. This rotation requires a stronger core from a rotational standpoint. The key movements in training your body for the modern golf swing is rotational.
If you could only spend 15 minutes a day on your body, you would spend all of them doing core rotational strength and flexibility movements and drills. This would give you maximum return on minimal investment.
Training your body off the course will take your game to another level. Focus on the key aspects I mentioned above to create the most power. Learn the fundamentals of the modern golf swing.