Your Body: The Why’s of Muscle Soreness

In my spare time, I like to exercise. There are a lot of good reasons for this, the buzz of endorphins, the health benefits, the joy of challenging myself and my body, and of course the serious need to balance out my inordinate fondness for cake, but I can never remember all these very good reasons when I wake up the day after a training session and find that all my muscles have jointly decided that moving isn’t something they fancy doing today. Delayed onset muscle soreness, or DOMS, is a well-known phenomenon amongst anyone who has ever stunned their muscles into a workout, but it does always make me wonder… why? Not why do I do it (we’ve established it’s the cake, oh and all those other things, of course) but why do my muscles hurt in the days following exercise? I know the obvious answer, they’ve stiffened up and are sore, but what does that mean? What’s actually happening in there to cause me pain?

Well the answer is… no-one is quite sure, but there are some theories.

First, there’s a popular myth that the soreness is caused by lactic acid that has built up during the course of the exercise, but this cannot be true. Lactic acid is removed from the muscles within 20–40 minutes of finishing a workout, so there doesn’t seem to be a way that it can be involved in the 48+ hours worth of pain associated with DOMS. By the time you wake up in the morning after a killer workout, try to swing your legs out of bed and realise that your legs quite frankly don’t want to co-operate, the lactic acid has long left your muscles. Lactic acid is however what causes a lot of the pain during exercise; it’s responsible for “the burn” that fitness professionals are always encouraging us to feel, and love.

To get back to DOMS though, in 1902 Theodore Hough suggested that it was “fundamentally the result of ruptures within the muscle”, and whilst the precise details of this are still not fully understood, this does seem to be true.  Although ruptures within the muscle sounds quite serious, and a really good reason not to get out of bed “Look, I’d love to come to work today in the snow but I’ve ruptured my muscles, okay?”, it’s actually nothing more than teeny tiny tears in the muscles fibres.

To really understand how a muscle reacts to exercise, you need to understand how muscles work. Muscles are formed from fibres, which are in turn formed from smaller myofibrils.  Myofibrils are made up of a long line of repeating units that are able to contract. This small unit is called a sarcomere, and it is formed from filaments; thick ones called myosin filaments and thin ones known as actin filaments.  Together, actin and myosin form a tug-of-war team that contracts your muscles. And they’re really good at it. If tug-of-war was still an Olympic sport, and molecules could enter the Olympics, they’d get a Gold medal every single time.

An individual sarcomere, aka the world's greatest molecular tug-of-war team

An individual sarcomere, aka the world’s greatest molecular tug-of-war team

In order to contract your muscle, the myosin filaments bind to the actin filaments, and pull them closer. Of course, they can’t do this without energy, and unlike actual tug-of-war participants, they can’t eat loads of pasta and bananas to get their energy. Instead, they have to use the universal biochemistry energy molecule adenosine triphosphate, or ATP. Using energy from ATP, myosin grabs onto actin and hauls it inwards. You can see from the diagram that in the lower image the actin filaments have been pulled closer together and the sarcomere has shortened. If you imagine hundreds of little sarcomeres all joined together in a long line to form a myofibril, and then hundreds of myofibrils bundled together to form muscle fibres, and ultimately, a muscle, you can see how the thousands of sarcomeres, all doing their tiny individual tug-of-war at once, will result in one big overall contraction of the whole muscle. And that’s what we like to call the gun show.

That’s the basics of how a muscle contracts. When you exercise hard you force your muscles to contract repeatedly either very fast, in order to sprint, under increased load, in order to lift very heavy things, or over a seemingly abnormally long period of time, for endurance type stuff. If your muscles aren’t used to it, then the strain of doing it very fast, very hard or for a very long time, can cause some damage and tearing, particularly to the Z-disc, which is the link between sarcomeres and is therefore highly important for supporting and maintaining the structure of each contracting sarcomere.  It’s the crucial anchor of the tug-of-war team.

The current prevailing theory of DOMS is that the healing of these tiny tears is what causes pain over the days following exercise. The process of healing microscopic tears to the components of the sarcomere involves an inflammatory response from the body. All healing involves inflammation, you can see this when the skin surrounding an innocent little paper cut turns red and a little sore, for example. And inflammation is always associated with pain. It’s to make sure you’re aware that something isn’t quite right.

As I said earlier, the precise details of DOMS aren’t understood, but this is the best theory we have right now. It is important to know that DOMS doesn’t mean that you’re injured; the damage to the muscle is minute and unless something goes wrong, shouldn’t cause any larger injury. It’s also worth knowing that there is something called the “repeated bout effect”. This basically means that if you continually do the same things to your muscles, they’ll begin to get used to it and it won’t hurt as much, which is handy, really.

Unfortunately, currently there is no real way to prevent DOMS, aside from slowly building up your exercise levels to get as much benefit as possible from the repeated bout effect, and making sure you warm up thoroughly, so basically all the things you’ve already been told to do. Is there anything you can do to help it go away faster, though? Unfortunately for those of us who were hoping to stay in bed and eat cake to recover (cough*me*cough), one of the best things you can do is actually to get moving again. Gentle exercise and stretching will increase blood flow to the area, and this can help to speed up healing. Apart from that, all you can do is swear when you walk downstairs and look forward to the next workout. And I guess cake probably wouldn’t HURT either, right?


6 thoughts on “Your Body: The Why’s of Muscle Soreness

  1. Feel the buuuuurrrrrn…garrgh we had a games teacher at high school who, at the end of class would get us all to line up against the wall in a hovering position (bit like a wild wee stance) & put us in competition against one another to see who could hack it the longest then talk about lactic acid at length. Oh the pain

  2. I recently experienced DOMS so bad that even lying down was sore and stairs were an exercise in extreme pain management. I had lots of dessert and sympathy to make me feel better but the thing that helped the most physically was gently massaging the muscles for a while…

    • Yep, massage has a similar effect to gentle exercise I would imagine, it stimulates blood flow which should at least speed healing a little bit!

      K x

  3. Timely post since I am currently feeling the burn after an intense training session on Saturday. Yep, the pain is still here. Very informative, thanks!

  4. I had killer DOMS from spinning class and the only thing that made it go was massage and movement – even though movement hurt. I remember it most from my pre-injury climbing days when 48 hours later, I’d go to lift a tray full of tea and struggle with the weight of it as I took it up the stairs. I kind of miss that feeling though – I think that makes me a bit weird.

  5. Pingback: Weekly Round-Up (Jan 21-27) | scicommnetwork

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