Once you get into the habit, a few minutes of relaxing into a stretch (and it doesn't have to be reminiscent of Mary Lou Retton) can feel downright great.

Two easy rules to follow:

• Don't bounce.
  Bouncing into a stretch is so fulfilling, isn't it? Suddenly, our heads hit our knees, and we have visions of gymnastic fame. The problem is, our savvy bodies know better. So they kick in a response that fires off a few neurons that actually tightens the muscle when you bounce. Huh? Pure protection. Our body is freaking out that we'll go too far and pull something. If it tightens down, no chance. No chance of injury, but also no chance of good stretching. Morale of the story: No bounces.
• Hold a stretch for 15 to 30 seconds.
  Have you ever seen this picture? Jogger saunters outside for a workout. A couple of bounces to touch the toes. Twist the torso abruptly one way, then the other. Throw a leg up on a bench, lean over it for a nano-second. Switch legs. Then off down the street, satisfied the stretch requirement was fulfilled. Morale: Hold the stretch, and don't let that picture be you.
  
  But how much should you do? Only recently did the sports medicineresearch gurus decide to tell us that. And it's pretty straightforward: Stretch major muscle groups 2-3 days a week to help avoid injury and maintain strength. All that means is you should stretch for a few minutes after each workout.
  
  Actually, stretches before a workout should be easy and are only meant to loosen you up. The real flexibility session comes afterward, when our muscles have turned into supple taffy. Pay special attention to the part of the body used in your activity, for example, shoulders for tennis and legs for cycling, but that doesn't mean ignore everything else.

Several muscles are important for everyone to stretch, all the time. If these are tight, low-back problems could strike:

• Hip flexor muscles (one set is at the upper part of your thigh, that thick cord that sticks out when you lift your knee) -- To stretch them while standing, lift your heel to your buttocks, grabbing the ankle with the same hand as leg. Tighten your abdominals, push your hips forward slightly while you push your ankle away from you against the resistance of your hand. The same stretch can be done lying face down on the floor. Caution: Do not pull your foot toward your buttocks because that stretches knee ligaments, which are not meant to stretch. Ever.
• Hamstrings (the group of muscles behind your leg) -- Place the heel of one leg on a low bench or step in front of you. Place your hands on your hips. Look straight ahead. Stand tall and pull back your shoulder blades. Reach the chest forward (not down) until you feel a slight pull behind the extended leg.

Final words to muscle warming and flexibility. Hot tubs, hot showers and hot packs won't do it. They warm your brain more than your body.