What exactly happens in your muscles when you stretch?

Dr. LloydSan Francisco Chiropractor

Reading Time: 6 minutes

All my life I’ve been told that I need to stretch. Everyone knows that you have to stretch. Except, I’ve always been a little bit against the cult of stretching. First of all, when you stretch before an athletic event, you have a higher chance of injuring yourself (It’s more important to warm up, which is a totally different thing.) However, it’s universally accepted that it’s good to stretch after vigorous activity. I’ve always felt that exercising a muscle is far more effective for keeping it healthy than stretching is, and I stand by this argument.

Now, it’s time for me to put away my bias against stretching, though, and tell you exactly what happens when you stretch.

Why stretch?

You need to ensure that you have good mobility of all of the joints in your body. Mobility means that your joints go through their full articulation range of motion (without going too far or subluxating), and going through this motion with full, healthy strength in the muscles and ligaments that control the joint. Full, strong mobility is essential for your quality of life. If one body part has too little mobility, then another body part has to take up all the work, and can become damaged or over-fatigued.

Muscles have to be strong, but they also have to be fully extensible. That’s where stretches help.

The soft tissues surrounding your joints can shorten due to lack of movement like when you are stuck sitting at your desk all day, or if you are on the couch all evening. Your ligaments and muscles also shorten and lengthen in the wrong places when you have bad posture, too. If your head is jutted forward all day, you will want to do some postural stretches. Past injuries can make your joints stuck in a certain position and preventing full range of motion; stretching is essential for this. you might have a problem that you were born with or has developed as you grew up, like scoliosis, that you need to stretch out.

Loss of mobility can really affect the way you move about your day and ultimately the way you can take care of yourself. Imagine being 70 years old and not being able to use your shoulder to reach around or not being able to use your hips to squat on the toilet. That’s when your kids take you away and lock you up at Merrill Gardens so someone can wipe for you.

You should know what contracture is.

Contracture is defined as the adaptive shortening of the muscle-tendon unit and other soft tissues that cross or surround a joint that results in significant resistance to passive or active stretch  and limitation of ROM, and it may compromise functional activities.

Contracture is when your muscles, tendons, and ligaments are shortened. It’s adaptive, so your muscles have adapted to sitting all day, and they have tightened up in their new position.

Some sources say that contracture is a complete loss of motion, where others use it interchangeably with “tightness” or “short.” The focus of this guide is not to talk about a clinical impairment that you’ll never be able to stretch out without manipulation under anesthesia. Rather, we are going to talk about stretching for the average, functional athlete, office worker, and person with tight hamstrings.

What happens to an unused muscle?

An unused muscle degenerates just like a joint does if it doesn’t move. When you don’t use a muscle, it atrophies. It gets smaller. It gets diseased too. When you don’t use a muscle, the fibrous filaments called sarcomeres start to get reabsorbed by the body. This is called sarcomere absorption and this is how muscles shrink if you stop working out. Along with losing the functional parts of your muscles, your muscles go from lean and efficient to fatty and fibrous. Fat cells start to go in between the layers in the muscles and make a new home. Collagen fibers grown in these same layers and start to velcro themselves to the muscle layers.

They say that once you start using your muscles again, you will reverse this damage, but that only goes so far. Stretching muscles that have shrunk because of disuse can break apart the velcro adhesions left behind from the fibers and allow you full mobility again. Stretching is not enough, though because you still need to actively move your muscles. And by actively moving your muscles, you have to put in the effort. Your brain needs to send a signal to the nerves going to your muscles to tel your muscles to contract against resistance and through full range of motion.

Healthy muscle
healthy
Atrophied muscle
sick

Exercise that sick muscle!

So what happens when you stretch?

When you stretch, your muscle lengthens a certain percentage. This is called sarcomere give. The telescoping fibers in your muscles slide apart until they are caught by the signals from the nerves and/or from the limits placed from the connective tissue surrounding the muscle fibers.

When you hold that stretch, there are two things that are probably happening.

  1. You are stretching the connective tissue of the muscle, including the ligaments that surround the muscle itself like Saran Wrap and the tough tendon as it moves to attach to the bone. This fiberous tissue gives a little with its elastic quality. While holding the stretch longer, you are testing the connective tissue’s viscoelastic properties. It will lengthen and won’t shrink back into position for some time. The longer you hold the stretch, the longer it will hold a new length.
  2. The microscopic filaments in the belly of your muscle (the sarcomeres) are slowly being more and more lengthened. Special sensors in the muscles called muscle spindles are relaxing their tight grip on the set tone and length of the muscle and it is allowing a small amount of relaxation to happen. At first, there’s a big fight as the reflex is triggered, but it may give up after a minute of a gentle stretch.
Muscle spindles regulate the length and tone of the contractile elements of your muscles.

Muscle spindles regulate the length and tone of the contractile elements of your muscles.

If you are stretching an unused, atrophied muscle, like your hamstrings that you sit on all day, you are stressing the fatty and fibrous connective tissue that has marbled your muscle. You are pulling it apart. You are stimulating it to go away. Slowly and gradually. As you work this out, and with more muscle exercise, you will resorb more and more fatty infiltrates. You will make more healthy muscle fibers. Your muscle cells will build more mitochondria, which helps create more energy.

When I first started looking into “what happens when you stretch a muscle?”, I first thought that I would have to explain away the complex neurology between the muscle spindles in your muscles, the golgi tendon organs in your tendons and the nerves that travel back and forth between your muscle and spinal cord and even the inhibitory neurons from the brain.

It turns out that stretching only has a temporary effect on the length of the active contractile fibers. When you stretch your muscles and you trick them into becoming longer, it only lasts so long, then the nervous system rests itself to its normal tone. Of course, this tone has to do with how well the underlying joint is moving, or not moving. You stretch, you return to normal.

They say that stretching actually influences the non-contractile elements in your muscles. This is that Saran-Wrap like sheath of tendon (epimyosin) that surrounds the muscle belly and any scar tissue adhesions that you developed over the years. It also includes the marbleized fat inside your muscles when you don’t move them.

What does marbelized fat in your muscles look like? You've seen fatty steaks before. It's the same thing. Good for steaks, but bad for your own muscles.

What does marbelized fat in your muscles look like? You’ve seen fatty steaks before. It’s the same thing. Good for steaks, but bad for your own muscles.

Does chiropractic stretch the joints?

Just like your muscles can develop contracture that makes them shorten and tight, your joints can develop contracture too. You can get fibrous adhesions in your joint capsule that will restrict motion. When your joints don’t move well, they signal your muscles to guard against too much movement. This can happen quickly, even if your joints are relatively healthy. Think about the burning sensation you can develop in your shoulders from sitting too long. Your muscles are reacting to being fixed in one place for too long. The muscles in your spine are particularly vulnerable to this.

If you’v e had a chiropractic adjustment, then you know the relief that you get when your joints move better. Your muscles relax with it. Chiropractic will take an immobilized joint in your spine and make it move better. In some cases, it will free up adhesions so the movement is permanent.

Action steps.

Yes. Keep stretching short muscles. However, if you are already really flexible, then avoid stretching muscles that are already too long. If you are working on muscles that are short, atrophied, and diseased, then you also need to exercise that muscle. Your tight hip flexors need to actively move as well as being stretched.  It sounds counterintuitive, but a short, hurting muscle needs to contract too.

Stretch those tight hamstrings, but also do some deadlifts and lunges to rehab them to their former glory.

Todd Lloyd, DC
chiropractor in San Francisco

Dr. Lloyd

I'm a chiropractor who specializes in correcting and relieving back and neck disorders. I have found that when you increase the mobility of your spine and joints with chiropractic care and follow up with this with improving muscle coordination with targeted exercises,then improving your function will also improve your pain.