I can only assume that many people do this simply because they don't realize the impending danger, so let's change that and look at why this happens.
Why is a tight muscle so susceptible to injury during sports activities or a workout? Look at it this way: if a muscle is tight, it is basically stuck in a contracted state, even when you aren't using it. Whether it is 20% contracted or 40% contracted, even when you are not actively engaging the muscle, that muscle is holding onto a pattern that it has gotten locked into, and you are not getting the full use of it.
For one, a muscle like this is weaker than usual. If your muscle is already 20% contracted at all times, you are only getting to use 80% of its strength. A tight muscle is also a starving muscle. It is not getting the
That gradual process of spreading dysfunction is not the only problem. Many people find themselves with injuries that occur quite suddenly and unexpectedly. If a tightened muscle is not addressed, it will typically only get worse over time. It gets tighter, and tighter, pulling harder and harder on itself and the tendons it is connected to, until one day you suddenly contract it during explosive movements, such as sprinting or pitching, and it pulls so hard a tear occurs. The tear may occur in the muscle, though quite often it is the tendon. There is also the danger of pulling your skeletal structure out of alignment. Maybe nothing tears, but those muscles are attached to bones, and what happens when they pull so hard the bones get pulled out of place? Pain, and a lot of it. That most often occurs in the spine and hips, as to where tears are more often in the shoulders (rotator cuff) or legs (hamstrings, meniscus, etc.).
There are many ways to prevent these injuries. Adequate warm up before activities is vital (very vital - make sure you are getting good and warmed up first), and thorough stretching afterward, as well as daily stretching. Save the extensive stretching for after the workout, as static stretches fatigue muscles, and you don't want to do that right before using them at full capacity. Using a foam roller, lacrosse ball, tennis ball, as well as any of a number of tools out there to assist with stretching is a great way to keep muscles loose and healthy. Getting regular massage, one to two times per month at least, in addition to the daily stretching, will do wonders to keep muscles in good working condition. Therapeutic or sports massage is also sometimes a necessary intervention for muscles that are stubbornly locked into a harmful pattern, or have recovered from injury or surgery but are still limited in range of motion due to scar tissue.
Keep in mind that if you have a nagging shoulder, hip, what-have-you, but you think it seems fine once you get warmed up, it isn't! Whatever is nagging you is NOT all gone just because you warmed up. The problem is temporarily masked, and you can still be injured, so be mindful. When in doubt, take precaution and get the issue addressed as soon as possible.
From the studio of
Licensed Massage Therapist