As a basketball player in high school, I favored the Bill Walton style of play. In other words, run hard, go for every loose ball, don't slow down till you're physically unable to keep up. Unfortunately, along with concrete courts and my complete ignorance of joint health, long hours on the court left me with a myriad of knee and ankle injuries- most significantly, a fractured right ankle and a 2 year long bout of tendinitis in the left knee.
However, these incidents introduced me to the importance of fitness in injury prevention. In fact, after 2 years of visiting the best orthopedists in the tri-state area, a rather scruffy doctor with terrible bedside manner actually found the cause of the problem- tight calves. Apparently, he had seen similar problems in Army recruits because of the extended running on hard surfaces- meanwhile, every other doctor had suggested an indefinite schedule of rest and ibuprofen.
The realization struck me- I had missed two years of basketball (and I believe, a chance at a scholarship) because of a TIGHT CALF. Clearly, stretching was more important than I had given it credit for.
This brings me to fitness and golf- specifically, hip fitness. Like most rotational sports, golf requires you generate and absorb a huge amount of force with your hips. The fact that these forces are asymmetrical and repeated in huge numbers (especially at the range) only increase the possibility of injury due to decreased mobility/strength or muscle imbalance. Proper hip health is key to preventing back/hip injury. The fact that the greater range and ease of motion should allow for a more powerful, free flowing swing is a bonus.
In golfers, there are two specific problem areas I'd like to address- the hip flexor and the hip rotators. Studies show that limited hip mobility highly correlated with back pain (http://www.mikereinold.com/2009/03/low-back-pain-and-hip-motion.html).
This very basic hip flexor stretch should be held for 30 second to a minute and performed on both sides. Hip flexors are often very tight due to a sedentary lifestyle. Extended periods of sitting tend to tighten the hips and weaken the glutes.
The supine bridge is a great basic exercise to strengthen the glutes. Personally, I found that my right glute was weakened due to my earlier ankle injury, which puts me at greater risk for back injuries due to asymmetry. This is further exacerbated by the fact that the left side of my back is stronger, as I am a right handed golfer.
Finally, internal hip rotation is often limited by tightness in the external hip rotators, which have to absorb the force of our swing (particularly on the left side). My ankle injury caused me to develop compensations in my gait leading to limited internal hip rotation on the right side also.
If you visit that video directly, there are a coupe of other internal hip rotation stretches also.
These are just a start! In order to maintain a healthy back through the rigors of golf (and life) hip mobility and core strength must be exercised in all dimensions, not just the few stretches I've shown here- these are just a starting point.