When they say a muscle is torn, it is a very ambiguous statement to say the least. The term gives no indication of the severity or degree. So here I would like to define these terms and what they mean within the context of competitive sports and casual everday injuries.
A muscle gets injured when it is taken forcibly beyond it’s threshold for elasticity. You see muscle is like a telescoping sausage. First, muscles are like sausages because each muscle group has a casing, which they call the fascia, much like the skin of your favorite deli sausage, it allows for the muscle to move within it’s specified boundaries while decreasing the chances of the muscles tearing. So in a way this fascia is crucial the the strength of a muscle group while keeping them organized for a specific use. Secondly, the skeletal muscle itself is like an old ship captains telescope where they pull it out to elongate. Muscle contraction is like this. When you shorten a muscle (i.e. contract) the individual muscle fibers pull each other and layer themselves on top from end to end “telescoping” on each other and this is why your bicep is bigger when you flex your elbow. Relax and the individual fibers release allowing the muscle to elongate and stretch.
When a muscle has gone beyond that point at which the muscles can no longer stretch they can either tear or snap completely off. The latter happens when violent forces interact on those muscle, say for instance you were trying to catch something that was heavier than you’re able to lift, the muscle would violently reach and go beyond that elastic threshold and like a rubber band will snap. The resultant “pop” sound and pain will be instantaneous. If the muscle was torn completely from its insertion point, or anywhere along the length of it, you may see the muscle curl underneath the skin leaving a bulbous deformity. When this happens to the biceps muscle we call this a popeye sign.
When a muscle is not completely torn off its junction with a muscle, then the injury is not a full tear and said to be a sprain or strain. The use of the word tear is correct in my opinion, just ambiguous, because tearing describes the mechanism that happens to the muscle very well. It tears not like a piece of paper, but more like a rubber band. Find an old rubber band in your desk. Notic how when you stretch it there may be some tears in the rubber that compromise the elasticity and the amount of loading or force that can be applied to it before it gives way at that tear. Notice how the tear is obvious when you stretch the band and how it shrinks back unseen when you let it go. That is much like how the muscles operate, only they are constantly repairing those tears. In fact, the swelling that occurs when you sprain your ankle is an important part of the healing phase, because fluid helps to wash out the tear and the inflammation (redness, swelling, bruising) and bring in much needed proteins to fix the tear. Ice is an athletes best friend when the swelling pushes the joint contents too far, or the irritation is just too painful.
Sprain and strain are basically the same mechanism, the difference being that sprain refer to the “tear” at the ligamentous (ligaments, tendons, and fascia) level, or closer to where the muscle is connected to the bone. A strain happens in the meat of the muscle further away from the connections to the bone. The biggest difference here is that strains are usually easier and faster to heal from because the muscle’s have more vascularity. That is to say there are more blood vessels in the meat of the muscle making it a quicker mend, ligaments having less blood to heal it. That is why some ankle and knee sprains can take longer to heal than a hamstring tear, though the tear in the hamstring is sufficiently larger.
A good example of this is baseball players who deal with “rotator cuff” injuries, especially pitchers. The rotator cuff is a series of muscles (all connecting on virtually the same place of the arms) mostly covering and on the underside of the shoulder blade that is responsible for many of the shoulders range of motion. Whenever we move our arms where they are connected to our upper torso the rotator cuff is in use. It isn’t the hard throwing of the baseball that can tear the rotator cuff (usually the suprasinatus muscle). Actually it is the rebounding motion of the tendon after the ball has left the throwers hand as the shoulder muscles are returning to their resting position. So in a way, the rebound of the muscle is a force greater than the ligament can bear and will commonly snap or tear after the muscle has reached its full length after release of the ball and not before.
If the tendon is put through this type of punishment day in and day out, the body doesn’t have enough time to spot repair the tendon and you get a chronic condition called tendonitis resulting from constant inflammation of the tendon for whatever reason. Tendonitis for too long becomes tendinopathy or tendinosis. Remember that all structures are dependent and affect adjacent structures. So if a muscle is even slightly torn, the fascia is scarred as well and the nerve to that muscle will be irritated affecting other muscles that need to take up the slack, so that after themuscle itself has quickly healed, the tendons will be tight from disuse and the fascia will have adhesion to the muscle which may require therapy depending on the severity of the injury, how well it has healed, and other factors like age must be accounted for when giving a prognosis (or usually how long until they can play again).
A complete tear may require surgery to stitch the muscle or tendon back onto the bone, but chances are that if it isn’t a full tear, then it is just a matter of time before it heals, but you may want to see a chiropractor or physical therapist to help it heal faster and correctly because though the muscle may heal itself, the tendon and fascia irritation can last for much longer and can limit the use of the muscle because of chronic pains. Consider surgery on incomplete tears only if you need the muscle function to perform properly for your occupation, are a high performance athlete and need to get back on the field (and a chronic injury can change your throwing motion), or just like to throw away a lot of money cause surgery is expensive and always get a second opinion from different kinds of doctors (like a chiropractor, doctor of osteopathy, or surgeon who specialises in that body part). If it a joint or ligament that is weight bearing like the knee please see your chiropractor so the problem doesn’t start to affect other structures needed for walking.