In my last column I talked about the importance of muscle endurance: the ability of a muscle to perform an action continuously over a period of time.

At a cellular level our muscle fibres have a propensity for either fast strength or slow endurance movements and different muscles are composed of varying proportions of either the ‘fast twitch’ or ‘slow twitch’ muscle fibres, depending on the job they are designed to do.

As individuals we genetically inherit the composition of our muscle fibres, although we have the power to change our muscle fibre make up through physical training.

Marathon runners will have a large number of Slow Twitch, or endurance, fibres, partly through genetics and partly through training.

Think of how someone who is quite unfit can gradually over time manage to run a marathon, they will have increased the number of Slow Twitch muscles fibres in their leg muscles.

Equally, a fit sprinter (fast twitch) will need to increase the proportion of slow to fast twitch if she wants to compete in long distance.

Fast twitch muscle fibres can generate power but will fatigue quickly. There are large quantities of Fast Twitch in the arms, for example.

It’s possible to train yourself to increase your repetitions of exercises like push ups or pull ups, rather than just being able to do one.

This type of training increases the amount of slow twitch fibres in your arms and shoulders giving you more endurance in your upper body.

Not all muscles are the same and the muscles in our body have different tasks to perform in order to keep us alive and moving. Think of the heart: it’s a muscle with a very specific job. The intestines too. Unless something goes wrong we never think of these muscle groups.

When we think of a fitness programme we tend to think about strengthening our limbs, maybe working our butt, getting a flat stomach or a great set of abs. Maybe doing some cardiovascular work like running or walking. All this stuff is great and fun to do, but what about the muscles that actually hold us up and give structure to our skeleton?

If our posture is poor or we have a problem with the mechanics around a joint then we can work out ‘til the cows come home but we won’t be able to improve those issues.

Our postural muscles lie close to our bones and work in a very particular way to support our joint structure.

They are composed of mainly slow twitch muscle fibres and have to do to the job of keeping the structure of the body in good alignment so that the superficial muscles which move us about can do their thing.

If our postural muscles are not up to the job, perhaps through lifestyle or injury they have become lazy or inhibited, our movement muscles have to take over the job of holding our skeleton in place.

Next time, I’ll talk about targeting the postural muscles.

Patricia Issitt is a movement therapist and Pilates instructor. She opened York Pilates Space, a fully equipped Pilates studio in the city centre in 2004.