Let’s look at how we contract a muscle and why that might cause it to ache.
When a muscle is contracted it uses something called ATP (adenosine triphosphate) a small amount of this is stored in the muscle itself and can give us about 3 seconds of strong movement, once this is depleted and if we decide to keep moving then the the body needs to make more and quickly.
For high-intensity, short duration activities, such as an explosive jump, or opening a heavy door, ATP re synthesis needs to occur very quickly. For this we use the CP system (Creatine Phosphate). It uses CP stores with in the muscles in to rejuvenate the ATP for reuse. This chemical reaction is very rapid, but CP stores are limited so they are depleted in a maximum of 10-12 seconds.
If we want to move for longer periods of time at a low to moderate intensity such as walking or light jogging then the Aerobic system kicks in. Aerobic metabolism occurs when the liver converts stored glycogen into glucose and sends it to the required area of the body via the blood stream, this combines with oxygen to create much more ATP. The waste produces of this are heat, water and carbon dioxide, which is why we get hot, sweaty and breath more heavily when exercising. This process can keep our body moving for almost a limitless length of time as long as there is fuel to burn, but does have its limits.
If we move into a higher intensity of exercise than the aerobic system can cope such as running or climbing stairs quickly the Anaerobic metabolism kicks in. It makes ATP from glucose without any oxygen, a less efficient and complicated process involving 12 chemical reactions which results in a combination of acids and other waste products. The body quickly and efficiently breaks these down into components and either stores them for later use or removes them from the body. But if we’re exercising so hard that the recycling system can’t keep up, then we feel the negative effects of an increase in acidity levels, causing our muscles to burn, ache and fatigue making it difficult for muscle fibres to function properly. If we stop contracting the muscle and rest, give the body’s systems a chance to catch up, then full function is restored and the pain slowly fades, this can take anywhere between 20 minutes and over 2 hours.
Please note that sore muscles during exercise and any pain you may feel 12-48 hours after are different, this after effect is known as DOMS (Delayed onset of Muscle soreness) and research suggests that it is a result of structural cell damage, take it easy as your body repairs itself and return to exercise only when you feel fully recovered.
Back to why tight muscles ache. At their core muscles are a simple mechanism designed to contract and release, contract and release again and again and again. When they are in their resting state the body removes the waste products and with it the pain and restricted movement.
But what happens when they are in constant contraction? The waste removal system can’t function effienctly, the range of movement remains constricted, the build up of acid isn’t broken down and recycled, causing constant stiffness and pain.
Another side effect of this build up is how the body processes lactic acid, one of the byproducts of the Anaerobic System, during the recycling process the body breaks lactic acid down into lactate and hydrogen irons. The body takes care of the hydrogen irons by converted into water and carbon dioxide. When the recycling system can’t keep up the build up of hydrogen, contributes to the in-balance of the muscles PH levels causing burning sensations and aches. The lactate is carried by the blood back to the liver, where it is converted into glucose and either consumed as energy or stored as glycogen for future use. However recent studies have shown that a build up of lactate is linked to anxiety. Unsurprisingly people who suffer from anxiety have increased tension in their resting muscles, therefore more lactate in their blood. But this can go both ways, we can make ourselves anxious by injecting lactate into our blood stream. This shows that although anxiety can cause muscle tension, excessive muscle tension can also cause anxiety, creating a cycle of stress and pain.
But if we retrain the nervous system to reset our contracted muscles, keeping them in a resting state until needed, the bodies systems can keep our ph levels balanced and us calm and pain free.