Your body is your most important piece of equipment.
You need to take care of it. Just like it's important to fill up your engine with the right fuel, you need to treat your body as you would a car: Think of the nutrition you put in as the fuel, and things like massages and acupuncture, as regularly scheduled maintenance to keep everything running as smooth as possible.
We've seen people spends $1,000s on the best bikes, golf clubs, tennis racquets, etc..but not a dime on their actual body. That would be like spending money on a great stereo or a new paint job but never changing the oil or timing belts. You'll only get so far before things breakdown. You can't go day after day without hydrating, fueling and recovering, and you can't go day after day after day without recuperating. You eventually will stop performing at your best.
Additionally, a lot of pain and injuries can be prevented or managed through proper form and technique. Pain is a signal from our bodies that something isn't right. Many times all we need to do is take a step back and look at the underlying biomechanics and make sure we aren't working against ourselves and forcing the body into strange or awkward positions. Something as simple as a proper bike fit can solve all sorts of cycling pain. Same thing for running, golf, tennis, or any sport. Seek a trained professional to evaluate your form and help correct any flaws.
Lastly, it's important to be both strong and flexible. And lesser know, it can actually be dangerous if you are only one of the two. Being extremely flexible can put your body into compromising positions if you don't have the strength to support it. And being very strong but not flexible can result in having very tight and limited range of motion. Strength and flexibility must go hand in hand.
If you do have pain, multi-sport Coach Adam, from Breakaway Training in San Diego has some tips for treating your pain:
A lot of low back pain comes from tight hamstrings and weak abdominals. In addition to focusing on strengthening the back, focus on lengthening and strengthening the hamstrings via standing hamstring stretches, and stretches with bands while lying on your back. Also basic strength exercises like bridges and opposite leg/arm extensions and raises while on hands and knees.
Again much knee pain comes from tightness in the quads and calves. Simple quad stretches, and extensions as well as calf stretches and raises. Squats and lunges are huge as well but with existing knee pain you need to be especially careful with form. Never let your knees travel in front of your toes and keep the weight and push coming through the heels.
The neck for many reasons can be very very fickle. Work to gain mobility through very very soft stretches and range of motion exercises such as careful turns side to side (think shanking head no), up and down (think nodding yes) and dropping your ear to your shoulder. Neck pain can originate from a whole slew of sources including the shoulders, traps, lats, and even stress.
General exercise has been shown to help arthritis by strengthen muscles around joints and maintaining bone strength. Low impact aerobic exercises like cycling or swimming are great options.