Dr. Mitch Broser
If you want to live a healthy lifestyle and train, I think it’s really important to have a general understanding of how muscles work. I don’t mean memorizing textbooks of muscle names and functions – I mean, how do muscles work in general? What is a muscle made of, and when I contract it, what happens? And how do muscles work in coordination to make complex movements? Understanding some basic muscle anatomy, physiology and biomechanics can help you look at your training from a different perspective.
There are 2 basic components of a “muscle”. The first is active muscle tissue, called sarcomeres. These tissues work with the nervous system, contracting to produce muscular force and human movement. The second component of a muscle is the passive connective tissue – the living elastic glue that holds the components of muscle together, tensioning as muscle contract and transmitting force to other areas.
Now, there are different layers of active muscular tissue and passive connective tissue. Let’s use your biceps as an example. Your biceps are actually 2 tubular muscles. They are wrapped in a stretchy but stiff connective tissue, just like the casing of a sausage. This is termed the Epimysium. Each muscle is made up of bundles of muscles cells call fascicles. It reminds me of a honeycomb – the perimeter of the honeycomb being the Perimysium holding together the whole honeycomb (the muscle fascicle), while each hole would be a single muscle fiber. Each muscle fiber is wrapped in its own connective tissue, the Endomysium.
These 3 levels of connective tissue (Epimysium, Perimysium and Endomysium) are cumulatively referred to as “intramuscular connective tissue”. This tissue is responsible for a lot of the passive strength, stretchiness and elasticity in muscles… At multiple scales! Very interestingly, the Epimysium, Perimysium and Endomysium all have connections with eachother and blend in with eachother at the ends of muscles. This allows for force to be transmitted to different levels of the intramuscular connective tissue and to different muscles! The transmission of force also comes with mechanotransduction – cells turning physical force-signals into chemical signals to allow the body to respond accordingly, such as stimulating muscular hypertrophy or muscular atrophy (disuse).
This intramuscular connect tissue plays a huge role in how muscles function. Let’s use the biceps example. When you complete a “bicep curl” exercise, you flex your elbow and bring your hand toward your shoulder. Your muscle tissues (sacromeres) contract and pull tension in the intramuscular connective tissue, from the surface of the bicep, down to the muscle fiber. This force is transmitted through the bicep and into any other muscle directly attached or close by. As you flex your elbow and your bicep muscle shortens, the muscle gets shorter and wider! This is because a muscle has a certain volume and as you contract the muscle, it must budge (shorter length, bigger diameter). This bulging influences the force signal transmission. As you continue to do your bicep curl, neighbouring muscles are recruited and work in synchrony to complete the exercises.
With training, we must remember that it’s very difficult to train a single muscle in isolation. That shouldn’t be the goal anyways! You can train specific movements and work on using as much muscle and tissue as you have available to complete that movement. As you continue to progress in strength training, your body will respond and adapt by making more resilient intramuscular connective tissue and the force will be distributed more optimally across more tissue. These adaptations we see are also across scales – from the level of the whole muscle (or groups of muscles), down to the level of a single muscle cell.
Reference:
- Purslow PP. The Structure and Role of Intramuscular Connective Tissue in Muscle Function. Front Physiol. 2020 May 19;11:495. doi: 10.3389/fphys.2020.00495. PMID: 32508678; PMCID: PMC7248366.