The body is made for many things, unfortunately we do have to maintain certain postures at times which are not received well by our bodies. This can lead to having some pains at times, but do not be too concerned about this. The most important thing is to try and maintain a straight back and to try and limit the extent to which you are lowering your head which can strain your neck.
Not all too much to be concerned with this, the greatest playing pains of the Cuatro are aspects not even mentioned in this video being the toughening of your skin and knuckles as you execute the frenados whilst strumming. Other than that, there are other pains which can develope, but just make sure you don’t sit down in the same positions for hours on end. and