Muscles

We have three types of muscles:

Cardiac - these make up your heart. They do not fatigue - we'd be in real trouble if they did! We don't need to think about it to make our cardiac muscles contract - they do so automatically thanks to the 'pacemaker' - a group of tissues on the heart surface that 'keep the beat.'

Smooth (involuntary) muscles - these work on their own and again we don't control them. They don't fatigue. An example includes the intestines.

Skeletal (voluntary) muscles - some of these we can control (e.g. biceps and triceps) and others act to support our movement. We might not think about which muscle groups we need to move, but this happens every time we do. Repeated or strenuous activity can lead to fatigue in these muscles, or pain, or cramps.

How do Muscles work

Muscles are attached to bones by tendons. Tendons do not stretch or compress.

Muscles can contract to become short and fat or relax to become long and thin.

Muscles work in pairs - e.g. the biceps and triceps in your arm. The bicep contracts and the triceps relaxes to bend your arm. Your bicep releaxes as your triceps contracts to straighten your arm.

Because these muscles work against each other, they're called antagonistic pairs.