Muscles. We are all made up of them, and in fact, we have around 600 of them. Just because you may have some that are not as visually prominent or noticeable doesn’t mean they aren’t there and working. They are fascinating, interchangeable and adaptable things. If you need evidence of this, just look at the feats of human performance on display at the recent Paralympics – people with whole missing limbs or visually able bodies but internally dysfunctional muscles out there outperforming most able-bodied people. This inspired me to write this blog and take you on a trip with me as we dive into your muscles and what forms them.
So, let’s start our trip at the surface level. We have three different types of muscles: smooth, which occurs in our internal organs and vessels; cardiac, which is unique to your heart and, which causes movement of your bones and their joints. For the purpose of this, we are going to focus on Skeletal muscle tissue, but I think it’s also good to understand we are made up of other types of muscles. You have various forms (shapes) shapes of skeletal muscles. Most of your skeletal muscles are fusiform, consisting of long parallel fibres and are typically involved in movement over an extensive range of motion.
Let’s get a bit deeper, shall we? Your skeletal muscle is encased (made up) by a form of connective tissue known as the epimysium. Within the epimysium are numerous bundles of muscle fibres, individually wrapped in a fibrous sheath known as perimysium. Within perimysium are muscles enclosed in a connective sheath known as the endomysium. An individual muscle fibre consists of a number of myofibrils – these are the contractile elements of muscle which means when we lift weights in the gym, we are contracting our muscles which is done through the myofibrils. Individual myofibrils are enclosed by a viscous material known as sarcoplasm and wrapped in a membrane known as the sarcolemma. Myofibrils consist of bands of alternating dark and light filaments of contractile protein known as actin and myosin, which are the sight of muscular movement (contraction). Contraction of skeletal muscle is done by the Sliding Filament theory; this is simply where a nerve impulse is sent to the muscle causing the release of a chemical called Acetylcholine. This chemical causes depolarization enabling calcium to release from the sarcoplasmic reticulum into the muscle cell. Calcium then binds with troponin, changing its shape and moving tropomyosin from the active site of the actin filament allowing myosin heads to bind to actin filaments forming a cross bridge. The myosin in the cross bridge using ATP, which is an energy compound that all cells use to fuel their activity and is what allows the myosin head to pull the actin filaments inwards, contracting the muscle. This will occur along the length of every myofibril in the muscle cell (that is a lot of cross bridges being formed!!). Muscle contraction will continue to occur when there are enough ATP and calcium stores. When there is no longer a nerve impulse, calcium will then be pumped back to the sarcoplasmic, causing actin to go back to its resting position where the muscle is lengthened and relaxed.
There are two primary types of skeletal muscle fibres, which are commonly known as fast-twitch and slow-twitch fibres). Most muscles contain both types of fibres, but depending on heredity, function, and, to a lesser degree, training, some muscles contain more of one type of fibre than the other. Fast-twitch fibres are large and white and appear in muscles used to perform strength activities. The slow-twitch fibres are small and darker (red) than the fast-twitch fibres (primarily because they have a greater supply of haemoglobin). Slow-twitch fibres are slow to fatigue and are prevalent in muscles involved in performing endurance activities. A runner with a higher percentage of slow-twitch fibres in lower-extremity muscles is more likely to develop into a distance runner. In contrast, a runner with a higher percentage of fast-twitch fibres in lower-extremity muscles is more likely to become a sprinter.
Now we have come to the end of our journey through your muscles and to be honest with you this is just the tip of the iceberg because If I was to take you on a full tour we would be here forever! In all seriousness, I hope you have enjoyed learning more about your muscles. They are a fascinating and complex part of our body where for a single simple movement like walking to occur, the body has to go through so many internal processes. I believe we sometimes take our body for granted, but when you read more into it, I know for me (and hopefully for you) we can find a newfound level of respect for how our body is developed.