Fitness Facts: Muscles can't push

This is a basic physiology lesson for all of you out there who are wondering what muscles to use for which moves. The principles outlined here will is useful for weightlifting, running, walking, yoga, cycling, martial arts…any kind of fitness pursuit, any kind of movement. Of course, the info here will be extremely useful for belly dancers.

Here is the lesson, summed up in three words: muscles cannot push.

Muscles are comprised of a large number of fibres whose job it is to contract. Contraction = pulling. Muscles pull. This contracting/pulling action has more than one purpose; in terms of muscular physiology, the term 'contraction' refers to the creation of tension in the muscle fibres, and that tension can be used to achieve different ends. When you are lifting something heavy, the muscles doing the work are shortening (contracting) to generate power. When you are lowering something slowly, your muscles are contracting in order to resist lengthening, thereby controlling how quickly they stretch. When your muscles are generating force to keep something in place, they contract and then hold that contraction to keep it constant.

There are three different kinds of muscle contractions, where the muscle is actually working:

Concentric contraction – muscle actively shortening - this is the muscle contraction that is usually occurring when people are thinking about muscles working. The fibres of the muscle are actively contracting so that they shorten, generating the sort of power required to lift a weight, or to flex your bicep (ooh la la).

Eccentric contraction – muscle actively lengthening - this muscle contraction isn’t used to lift or hoist, but instead to control movement and resist lengthening. The muscle fibres are engaged in order to control the speed and rate at which they are lengthening, resisting the outside force (it could be as gentle as gravity or as violent as gravity plus 40 pounds of groceries) acting on it. Grab something heavy and lower it in the most controlled manner possible – that’s an eccentric contraction. The muscle fibres are still contracting, in order to control the rate at which they release and relax.

Isometric contraction – muscle actively held at a fixed length - the purpose of this contraction is to maintain a constant force in the muscle to hold something in place. If you are holding a dumbbell straight out in front of you, your muscles have contracted with tension that allows neither lengthening (eccentric contraction) nor shortening (concentric contraction). Spending some time holding the plank position gives a great lesson on the strength and importance of isometric contractions.

The above information came primarily from this website, which has great info on the workings of muscles:

Muscle Physiology Home Page: Types of Contractions

Another fun site with interactive, animated info about how muscles work on a cellular level is Thomson Brooks/Cole study resources: Muscle Contraction

I was hesitant to post the following article because of the taint of unreliability that Wikipedia has acquired, but it is a good, solid explanation of muscle contraction and is consistent with the information in my print resources:
Muscle Contraction.

This sort of info is extremely useful to have on hand. I find that having a basic understanding of how muscles function, and which ones would be contracting and relaxing during a given move make moves easier to understand and execute. It doesn’t mean that I execute them correctly, of course, just that I get what they are in theory and hope that eventually my limbs will agree with my brain.