It's a very complex process, but presuming you're familiar with the structure of muscle fibres you need only to Google "Sliding Filament Theory". This is the way that the scientific community believes that muscles shorten, or contract. You should find loads of information on Google and Google Scholar for more indepth stuff.
They contract
Muscles contract and relax to move a joint. ... Muscles contract at a constant rate. Muscles contract and relax to move a joint.
If the papillary muscles fail to contract the valves will prolapse. The papillary muscles are located in the ventricles and contract to prevent prolapse.
you exhale (:
They contract and release to move your body
The internal intercostal muscles relax and the external intercostal muscles contract, pulling the ribcage upwards and outwards.
The muscles contract, while others move foreward, which allows the body part to move.
The muscles contract which in turn push the baby out.
When muscles contract, they shorten and generate force, allowing movement to occur. This process is controlled by the nervous system and involves the sliding of protein filaments within the muscle fibers.
You would get a heart attack otherwise known as a cardiac arrest.
When muscles contract, the brain sends signals through the nervous system to the motor neuron that supplies several muscle fibers. There are different versions of contraction, which includes voluntary and involuntary.
Your hair stands up and you get goosebumps