leg cramping at mile 20 of a marathon has little, if anything, to do with sodium. You can search pubmed for the multitude of leg cramps/electrolyte articles. Also has little to do with age either. Has mostly to do with pace/distance past training. Really just that simple. Now, if your gastroc is “locked” and what to do about it? Good luck - hurts though! In general, stretching the cramped muscle is not a good idea - just slow down (i.e. walk) to keep the blood flowing, then get going again if possible. For the elite, that will be a different slow down pace than us mere mortals for sure!