If upper or mid back, concentrate on the area in between your spine and shoulder blades (and lats). If your lower back, concentrate on your glutes and hamstrings...probably not a great idea to roll your lower back. I'm starting to think it can be done safely but I'm a bit scared/lazy to try yet...
Thoracic (upper back) mobility
Foam roller (not PVC pipe or rumble roller): http://www.youtube.com/watch?v=elWYs...edded#t=01m18s
Lie on your back with the roller beneath your upper back. You want to be careful not to move the roller below the bottom of your rib cage as you'll likely end up flexing your lower back (which should be rigid). Next, you'll want to put your hands behind your head to help keep your shoulder blades from hitting the roller before your back muscles. Then stretch your head towards the ground, being careful to let your upper back flex but not your lower back. Hold for 30 seconds. Move the roller up or down your back and continue. Given the diameter of foam rollers, doing this stretch in 2-3 places usually suffices.
. This requires the same setup as Thoracic mobility but instead of stretching into the roller, you roll it back and forth against your upper back muscles while relaxing into the roller. Note that while this will be helpful for beginners, once the surface knots in your muscles are broken down, you'll want to use a ball with this technique:
(This is the "Sticky Scap vid" which also shows stretching and mobility after the SMR technique)
Lie down on your back on a relatively hard surface. Put the lacrosse ball in between your shoulder blade and spine. Then relax into the ball and move your arm up and over your head as far as it can go (keeping it close to your ear as it goes by your head). Move your arm back down to your side and then repeat this movement several times, relaxing into the ball. Then move the ball up or down your back, finding new spots that are tight. Be careful not to go below your ribcage as you may start causing your lower back to flex unnecessarily.
More Advanced: To really hit some hard-to-reach rhomboid muscles, cross your arm in front of you and tuck the lacrosse ball against and under your shoulder blade - find a spot that is tight. Relax into the ball and hold. Then reposition the ball up or down the shoulder blade and repeat.
Another pro tip: Use your opposite hand to gently push down on your arm (above the elbow) when your arm is at full extension behind your head. This can help you relax into the ball while still getting optimal extension from your arm which should help clear up knots faster.
Lie on your side and place the roller under and below your armpit. Then roll up and down the side of your upper back where you lat muscle is. Rotate your body a bit to hit your lat from different angles and really relax into the roller.
Ball on wall: http://www.youtube.com/watch?v=elWYs...edded#t=03m55s
This can be convenient if you’re rolling your pecs already and want to transition into hitting your lats. Or if you have a particular trouble spot with your lats that you want to isolate and focus on. Stand with your side facing the wall and place the ball in between the wall and your lats. Then lean up against the wall, adjusting the placement of the ball to hit your lat from different angles and find tight painful spots. If you want to apply even more pressure, you can use this technique lying on the ground, just replacing the roller with a ball.
Ball on floor: http://www.youtube.com/watch?v=8caF1Keg2XU#t=02m45s
This can also be done lying down on your back with your body fully extended and crossing the leg of the glute you are SMRing to your other leg - so basically what this guy is doing but lying down. It will help get to deeper adhesions and also, it's extremely tough to relax into the ball using the technique shown in the video as it may hurt a ton (e.g. http://www.youtube.com/watch?v=J3dSu...eature=related
) in which case, definitely try the lying down on your back method for a few days or weeks until it’s not as painful.