Recently I did some analysis on an athlete’s sodium loss and cramping issue reminding me of an issue I had a couple of years back.
I had a sodium test done out of interest, even though I did not have a cramping issue. The recommendation suggested I take significantly more sodium than the norm due to my high sodium loss. I implemented this in my next race experienced severe cramping. In review we established my sodium intake was too high slowing my water absorption and causing bloating.
The issue was that the sodium test report did not show a relationship between exercise intensity and loss rate. My test was done at threshold pace, however my race was a 70.3 performed at close to aerobic intensity (Zone 2).
It is important to recognise that any recommendations on sodium intake should take intensity into account ans the difference between threshold intensity (Upper zone 4) and aerobic intensity (Low zone 2 – IRONMAN Pace) may be up to a third less!
It is also important to compensate for high sweat rates in hot races which will increase sodium loss.
Below is a link to one study and some reference charts showing the potential differences.