i used to carry mine, in and out of car, give it time you will get minor backache,
since putting it on a trolley my backache has more or less gone.
too much pressure on lower back, in and out of vehicle. im 15 stone and gym train regurally. i couldnt fathom why i was getting lower back pain, since i put it on trolley its eased right off.
mind ive been using backpack for over a 18 months.