Question: how does your muscles weaker

LauraAnne Furlong answered on 7 Nov 2016:

The strength of your muscles is determined by a few different things, such as the size of the muscle itself, how it is activated (so how your brain tells it to work), and things we call its morphology or architecture (a muscle is made of up lots of smaller part, and morphology is information like the length of the smaller parts, or the angle they work at when the muscle is doing a particular task). How quickly you can do something can also be affected by how the muscle is made up – fast muscles (which top sprinters have lots more of than the everyday person!) have more of what we call fast twitch muscle fibres.

The main ones that will affect it are the size and activation. If we have a big muscle, it can generate more force, just because it is bigger – think of the big muscles in your leg – they are much bigger than the muscles in your hand that move your fingers for example, so can generate much bigger forces. If you don’t use your muscles, they become much smaller and so become weaker. This is a real problem in space because of the lack of gravity on the space station (which means usual training exercises aren’t as effective), and astronauts can come back to Earth much weaker than when they went up. Because of this, NASA and the European Space Agency fund a lot of research into how muscle changes when it isn’t used and how we can reduce these changes.

How your brain tells your muscle to work can also affect how much force it can produce. Your brain tells your muscles to work, and cleverly, it doesn’t have to activate all of the muscle for every task you perform. It can determine how much force is needed to do something, so for example, if I needed to lift a cop of tea, my brain would tell my muscles to activate much less than if I needed to lift a very heavy weight in the gym. Anything that damages the pathways between your brain and the muscles can hence make muscles weaker, such a brain injury or conditions such as multiple sclerosis.