The range of motion is referring to the distance or the length of the movement you are performing. Our muscles are connected to our bones via tendons, and the muscle to tendons via ligaments. Technically, our body can extend and stretch and our joints can lock out to allow movement to happen. Take a dancer or a yoga instructor for example, their flexibility almost seems endless, their tendons, ligaments, and connective tissues are strong but supple enough to allow for the freedom of movement. However, movement can go too far and there is such a thing as connective tissues, ligaments, and tendons being pulled too far out of a proper range of motion. For dancers or yogi’s, their flexibility is mostly body weight driven so pushing their range of motion is not going to be as potentially damaging or harmful to muscle fibers, joints, ligaments, or tendons. That being said, anything stretched and too far beyond its range of motion and continually doing so does weakened the connective tissues, joints, etc. which can cause potential damage to the joint itself, or even tears, partial tears, sprains and strains. Usually once ligaments and tendons have been stretched to the point where there is a tear or possibly some of the connective tissue in the joint capsule itself becomes lose, then it’s very difficult to get that joint back to the strong structure it used to be. Shoulder dislocations for example, once that shoulder pops out of the socket, the connective tissue and the joint capsule also gets stretched out, which means those who suffer shoulder dislocations are highly prone to having it happen again and again. So just because your body can stretch that far, does not always mean it should!
When it comes to weight training, unlike dancers and yogi’s, you are now asking the muscle fibers to be stretched and lengthened while under load/weight. This is different, you are using and/or recruiting more of your muscle fibers to do the job, and on top of this, you are lengthening and contracting your fibers while controlling a heavy weight. Range of motion therefore cannot be as fluid or “stretchy”, the weight/load is a game changer and this is where muscle tension needs to be ensured. Making sure you practice engaging and activating the muscle while it is lengthening through the desired range of motion. You never want to be “loosey goosey” or using momentum through any phase, which is why muscle tension is so important. Never snap or completely lock out your joints, because then you are actually transferring the load and pressure onto the joint and connective tissues which are a lot weaker than your actual muscle belly. On top of that, every time you completely release or fully extend your joints, that is releasing your muscle of the work and gives it a mini break. You never want your muscle belly to be resting or taking a break during any phase of the working set. You break in between sets, never during. Never release tension off the muscle belly and keep within a range of motion that still ensures your muscle fibers are the one controlling the load and the movement, not momentum, connective tissues, or your joints.