In y last marathon, my calves cramped up on me pretty badly starting at about the 20 mile mark, causing me to stop a handful of times over the last 10k to stretch them out (and costing me 2:00-3:00 in the process). It was probably caused by some combination of slightly warm weather (Chicago 2015 - probably a little over 60 at the end) and fatigue from getting out too fast the first mile.
Recently had the same thing happen on a 20 mile training run that I did as part of my Boston build up. Another warm day, but there was also some cumulative fatigue from having done a workout 36 hours earlier.
I intend to take salt tabs to try to eliminate one variable, and I want to try them for the first time on my 20 mile long run tomorrow.
On race day, what practice do folks employ with respect to salt tabs? I'd like to emulate my race day plan as part of my training run.