“Buy a bag or briefcase with a wide, adjustable strap that’s long enough to reach over your head. A messenger bag (like the ones bike messengers wear) is made to wear this way. Having the strap on the opposite shoulder of the bag distributes the weight more evenly and helps keep your shoulders even and your back pain-free. When carrying a heavy bag or case without straps, switch hands frequently to avoid putting all the stress on one side of the body. To lighten the load, periodically purge bags, cases, backpacks, and other carriers of things you don't need.”

Ref: http://www.webmd.com/back-pain/living-with-low-back-pain-11/tips-for-pain-relief?page=2

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