its called deep pressure massage.
most normal back and shoulder injuries are tissue injuries. obviously this technique wont work with serious injuries like fractures and slip disks.
you have muscle, sinew and tendons in your back. when you tear a few fibres of these tissues, what happens in some of the interlinking fibres literally tear apart, the surrounding healthy fibres then tense up and this does two things, it stops ribboning happening along the line of the tissue, also the 'knot' around the damaged fibres prevents amino acids getting to the damaged fibres and therefore the damage cant heal.
so you need to break the walls of the 'knot' down. its like tenderising meat. when the knot is broken up a bit both the torn tissues and the knot can heal.
so find the area that hurts by using preferably your own fingers and pressing down till you find the part that hurts most, and get the exact right spot of tendon or muscle. the spend a few minutes pressing your fingers into it and massaging it. keep thinking 'tenderise meat' in terms of pressure. obviously this will hurt a bit.
you may have to repeat the process a few times to fuly clear a knot leaving enough time in between for some healing to take place, say a week.
finally if you dont want it back, when you go to the gym do a few 'face down sit-ups' or deadlifts, it works like a treat to strengthen your back.