Why Do Muscles Get Sore?

neuromuscular junction

I started working out about a year ago and found out that muscle soreness sets in pretty quick when you're speeding to work out. Maybe you want to realize the science behind this phenomenon.

To understand muscle soreness you have to know the basic anatomy of the muscles. We have two points of attachment. Also, we have the origin insertion. Each muscle has a specific action as well.

The origin is the point of attachment to a bone that doesn't move and the insertion is the point of attachment that does move. For instance, quad muscles are attached to the origin, to the pelvis with its origin, and to the patella tendon both its insertion. This allows the muscle to have the action of extending your leg.

Muscles also have certain characteristics as well. The first is contractability - an ability for the muscle to shorten also called a contraction.

The second is excitability, which is the ability to respond to stimuli from the brain. This is done to action potentials.

The third is extensibility which the ability to be lengthened stretched or extended.

And, finally, the last one is really important. It is the ability to return to normal length when relaxing, which is elasticity.

Right here in this picture we have a picture of a Neuromuscular Junction - this is where the nervous system meets the muscular system. You can see the synapse and the muscular fiber.

When you want to contract a muscle while working out, a stimulus from the brain sends impulses to muscles at the neuromuscular junction. A neurotransmitter called acetylcholine diffuses across the synaptic cleft and attaches to the ACH receptors. This depolarizes the muscle membrane, also called the sarcolemma, and releases calcium. It is the first step in a contraction.

Sliding filament theory

Thus, contraction occurs using something called the sliding filament theory

Your muscles made up of two different filaments, either thick and thin filament. A thin filament is called Actin and the thick filament is called Myosin. On the actin, you have two proteins called troponin and tropomyosin. When calcium is released, it binds to troponin, which pulls triple myosin out of the way and reveals something called an actin binding site. It allows the myosin to be attached to the actin using something called myosin heads.

Whenever the myosin attaches to the actin on the actin binding site it forms something called a cross bridge. The cross bridge pools actin and myosin together shorting the Z-lines. The shortening of the Z-lines is actually the contraction.

Myosin attaches to the actin and actually pulls them closer together. It shortens the Z-lines and performs a contraction.

And when you're wanting to relax something is released called acetylcholinesterase. The chemical decomposes acetylcholine and stops a stimulation for the contraction. Calcium is actively transported away and cross bridges are broken. All this causes the easy lines to turn a normal place causing a relaxation.

The Role of ATP

ATP is used throughout this process many times. The contraction and relaxation will be impossible without it.

Myosin heads use ADP and inorganic phosphate to act with myosin heads. ATP breaks the cross-bridges created before and head back to perform this action over and over again until contraction occurs.

On the picture, you see how the myosin is attached to the actin and how it is pulled with the release of ATP and organic phosphate.

If ATP then breaks cross-bridge and attaches to the myosin, it doesn't hide. It goes to hydrolysis, which gives it ADP and phosphate again and attaches, and pulls it and then does this cycle happens over and over again until contraction occurs. So, when you want to relax, basically, ATP breaks the cross bridge and then calcium goes away and the binding sites have no longer revealed.

Muscle Metabolism


Where does this ADP come from? The initial source of energy for muscle contraction is creatine phosphate. However, during strenuous activity, it only lasts about 15 seconds.

The next source of energy is cellular respiration. Here you have glucose which turns into lactic acid through glycolysis and then into 2 ATP.

When oxygen is present, it will go to the mitochondria for aerobic respiration and yield 36 ATP. If it doesn't, it goes to anaerobic respiration to create lactic acid. Without enough oxygen lactic acid accumulates, which is actually what causes the pain and muscle soreness.

So, if there's not enough oxygen get to your muscles, the lactic acid will build up and cause muscle soreness. This is something called an oxygen debt. The demand for oxygen is higher than the supplied during workouts and the oxygen will eventually be paid to rest in time.

While you're working out you only have a certain supply of oxygen. This situation creates the oxygen debt, which eventually is paid overtime with the rest.

How To Relieve Soreness?

The first thing is a proper diet. You will need plenty of proteins to help your muscles recover and repair better.

The second is the application of heat. This allows your blood vessels to widen allowing more oxygen to get to that area to clear the lactic acid.

Next is proper breathing. Make sure your body is getting the proper oxygen intake.

The next thing is correct body movements. This is important in order not hurt yourself using incorrect body movements. And the second you don't want to use ATP through muscle contractions that you don't actually need.

The last one is you have to work out more. This allows capillaries and mitochondria to form more in the tissues. Actually, it is the most important one. This builds up your circulatory system and is the best way to relieve your muscle soreness.