How to Prevent Muscle Cramping During Mandatory Posing

I had a posing practice session yesterday and my hamstrings cramped so bad I had to sit down for ten minutes. I am six weeks out and I am terrified this will happen during the actual show. I am taking magnesium and potassium but it does not seem to be enough when I am holding the poses for sixty seconds.

I have been told to increase my salt intake before posing but I am worried about holding water. It is a very fine line to walk during prep. I find that the back double bicep is the worst for my legs. I am trying to keep the tension but my muscles just want to lock up.

Is there a specific trick you use backstage to keep your muscles loose? I have seen people using mustard packets or pickle juice. Does that actually work or is it just an old wives tale? I really need to get this under control before I step on stage.