I have read that nearly 80% of Americans complain about back pain sometime in their life, usually nearer to the end of it. I am wondering what you can do when you're young, and what not to do when you're young, so when you're old you won't be part of that 80%. Any suggestions? Thank you.
It is smart to look at fitness when you are young with an eye on preventing problems as you age.
Back pain can have multiple causes. Some of the causes stem from degenerative changes of the joints, restrictions in the soft tissues (muscle and fascia), protective muscle spasms, disc degeneration and/or prolapse, and osteoporosis (weakening or thinning of the bones).
To address these causes your preventative program should address your posture, flexibility, strength, activity levels and bone strength.
Setting up an exercise program
Posture - Good posture is a combination of strength, flexibility, and breaking up periods of prolonged positions with movement breaks. Exercise for improving your posture are included here: I have extremely bad posture, what can I do?
Strengthening your "core" muscles such as your abs (transverse abdominis and obliques more so than the rectus), your back muscles (paraspinals, lats and multifidi), upper back and scapular muscles, and hip muscles. Squats, deadlifts, hyperextensions/reverse hyperextensions, planks etc. strengthen these key muscles. Other exercises and strategies for improving your posture are included in Optimal exercises for an abdominal workout.
Balancing left/right and front and back muscles is also important when planning your strength training. For example, over-developed and tight pectoral muscles protract the scapula (see protrated shoulder girdle) causing over-lengthening and weakening of upper back and scapular muscles muscles like the rhomboids and middle traps.
Flexibility - Most of us think in terms of muscle length, but also think in terms of fascial glide. A short daily stretching program, proper hydration and avoidance of prolonged static postures helps to keep you flexible.
Bone Density - One of the best things you can do while young is to increase your bone density through exercise and good nutrition. Resistance training helps to increase bone strength. Good nutrition including adequate levels of calcium intake and vitamin D are needed for healthy bones. Lowering your risk factors such as smoking, physical inactivity, and heavy alcohol intake help reduce future osteopenia/osteoporosis. According to the International Osteoporosis Foundation on bone health:
Childhood and adolescence are particularly valuable times to improve bone mass through exercise.
Minimizing Repetitive Activities or Prolonged Positioning - Repetitive shearing forces are wearing on the disc. Listen to your back and when it says enough, it is time to take its advice and change what you are doing.