Let's imagine that you're doing a hamstring stretch (as that's the one that usually elicits the most noise in class!).

As you extend your knee, you start to feel that familiar painful feeling in the back of your leg. This is your nerves sounding an alarm to warn you that they're not certain that this level of extension is safe for you.

As you hold the stretch, you notice that the sensation eases off. This is when I always say that your nerves have got bored and wandered off. 

But it's more likely that as they realise that nothing bad is happening, they stop sending the pain message.

You're then able to extend the stretch a little more. the sensation comes back; the nerves realise that nothing bad is happening; they switch off.

This means that if you stretch regularly, your nervous system learns that this level of extension is safe and over time, you are able to extend further.

Are the muscles actually getting longer during the stretch? Yes, some studies using ultrasound indicate that the basic units of the muscle (sarcomeres) do actually lengthen and become more pliable for an hour or so after stretching.

Quick answer here is that it depends.

Having a decent range of movement generally is going to make you less prone to those freak desk and sleeping injuries - you know, the ones where you move suddenly and BAM, your shoulder or back is locked up? 

If you're someone who does other sports and exercise, you've probably always been told to stretch before you start exercising.

The research here is a bit conflicting. What does seem to be the case however is that it's generally more beneficial than it is harmful for both injury prevention and for performance.

This is especially the case in activities that have explosive movement such as sprinting or jumping. Less so in endurance sports.

If you're giving me the confused look right now wondering how on earth stretching is going to improve your cardiovascular fitness....bear with!

A number of studies over the last decade have indicated that there's a link between being inflexible and risk factors for cardiovascular disease.

Why is that? It's not entirely clear. But there are a couple of hypotheses.

The first is that when you stretch, you're not only improving the elasticity of your muscles, but of your blood vessels too. 

The second is that hardening of the arteries (atherosclerosis) is an inflammatory condition which might be alleviated by the actions of the cells within our fascia secreting anti-inflammatory chemicals called resolvins as they're gently stretched. These chemicals turn off the inflammation response and so help the natural healing process.

(OMG, who else remembers that horribly patronising advert?  Sorry if you had forgotten it and I've now reminded you)

When we're stressed, we tend to tighten our muscles in response. This can manifest in shoulders, neck, jaw, chest area. 

If we've got reduced range of movement generally from sitting a lot (and from getting older), this can leave our bodies feeling uncomfortable, stiff and achy; and can also impede our ability to breathe fully into our lungs. 

So making sure that we release the muscles and enable ourselves to move more freely can leave us feeling calmer because we associate the feeling of being stressed with muscle tension. And as we open our chest, we stop breathing into the top of our lungs, and are able to fully fill them.

Deep breaths already make us feel calmer. So I'm a big fan of using our breath to aid our stretches. I particularly like the mindful moment it provides us.  

As we calm our breath and our bodies, this activates our "rest and digest" systems (in opposition to our "fight and flight" systems) and allows us to feel calmer, sleep more deeply and recover better.