Function of Skeletal Muscles in Breathing process

[JohnnyWhalen]

My anatomy & physiology text book tells me that the skeletal muscles are directly involved in the breathing process but doesn't explain how. I've tried the internet but not having much luck.
Is there anybody who could give me a brief overview of how they are invoved?
Any info would be much appreciated - many thanks!

[bednobs]

put simply your skeletal/intercostal muscles make your chest move in and out

[Dr Hungry]

Skeletal muscle refers to any muscle that is not smooth or myocardium (ie most muscles).
In relation to respiration: the internal intercostal muscles cause the ribs to move upwards and outwards (in a 'bucket handle' and 'pump handle' motion), and the external intercostal muscles reverse this process. Neither of these sets of muscles are generally needed during quiet breathing. The diaphragm is the most used muscle in respiration, during quiet breathing this contracts to flatten and increase the thoracic volume, hence pulling air in through the reduced pressure. This is inspiration. Expiration involves the relaxation of the diaphram and the abdominal contents pushing upwards to reduce thoracic volume. Also used more rarely are the accessory muscles, eg sternocleidomastoid and serratus anterior which increases the expansion of the ribcage, or the various abdominal muscles which expell air forcibly.

[JohnnyWhalen]

Thank you to you bednobs and also Dr Hungary for your responses - both of which extremely useful. I just don't understand why the textbook did not go on to give any explanation.

Thanks again!

[Dr Hungry]

You're welcome, although I foolishly got the words internal and external round the wrong way in the second sentence: the external intercostals increase the size of the thorax, the internals forcibly reduce the size, of course. Sorry about that!