Person A
Helder, I keep hearing people mention eccentric and concentric at the gym, what are they talking about?
Helder
Well, when we train with load, we lift weights repeatedly. Some exercises like the leg press, we begin by lowering the weight and then we lift the weight, other exercises like a bicep curl, we lift the weight and then lower the weight.
When we lift the weight, the muscle fibres inside the muscle shorten, this is called a concentric muscle action. When we lower the weight, the muscle fibers lengthen, this is called an eccentric muscle action.
Person A
What is the difference between the two?
Helder
We have to go a little deep into this so that you can really understand it. I will first tell you about the concentric and then we can return for another chat for the eccentric.
Person A
Sounds good.
Helder
Ok so, when muscles shorten, they produce force because of the actions of active elements inside them.
Person A
What are active elements?
Helder
They are structures that exert force by using energy to move in response to an electrical signal that is sent from the central nervous system.
We also need to consider that each muscle fibre contains long, thin chains of structures called sarcomeres, which are made up of many strands, also called myofilaments.
For active force production, the key myofilaments inside each sarcomere are those made of actin and myosin. When that signal from CNS arrives at the muscle fibre, it causes calcium ions to be released into the area around the actin and myosin myoflaments.
Person A
What does that actually mean?
Helder
Ok, so when you lift a weight myosin binds to actin, this binding process, which involves the formation of cross bridges, causes actin to slide past myosin in each sarcomere along the muscle, and this deforms the muscle. This deformation of the muscle fibre causes it to to bugle outwards. The outward deformation is what stimulates muscle growth.
Person A
There is a lot there to think about.
Helder
Yes, let this sink in for now and we will talk about the eccentric in the next blog
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