Your body weight is supported by a combination of your muscles and your skeletal structure, the more muscle you have the less load you will have on your skeletal structure. If you have weak core muscles and stabilizing muscles because you have focused on building your muscles from exercises that don't use free weights(using machines, or doing squats in a smith machine for example), then you could run into problems. You could also run into peoblems if you lockout your joints like your knees or elbows or generally have postural issues then that can place undue stress on your joints. If you are into strength training and you lockout your legs during barbell squats for instance, you are putting stress on your joints in your knees and can damage your joints over time. Same thing can happen if you lockout your elbows during an arm/chest exercise.
