Body's response to meditation I have been practising Vipassana meditation for some years now.
Please advise me: why on my in-breath do my toes contract, and most times relax on my out-breath?
Sometimes my toes stay contracted for quite a few in- and out-breaths, then my toes relax. My toes' contracting usually starts over half-way through my 45 minute meditation.
That's not all that uncommon.  If it's not your toes, it'll be something else.  Personally, my hands will sometimes contract by themselves and my forearms will occasionally rotate a few degrees.  Other people usually report muscles in their faces that start to fire, maybe their shoulders will bounce a bit, etc.

All this is a result of tension leaving the body.  The more you relax into your meditation, the more your body will loosen up.  The deeper the concentration, the more relaxed you'll get.  As you keep at your practice, you might even see other places start to loosen up - places of deep seated tension that you didn't even know existed.

It's nothing to be alarmed about if that's your concern.