Sweat sodium concentration varies substantially between people and can change with collection method and conditions. Visible salt marks may justify a closer look but do not quantify concentration or prescribe replacement. When testing would materially affect a long, high-loss event plan, use a valid protocol and interpret the result alongside measured sweat rate, normal diet, every food and drink source, conditions, access and tolerance. Avoid both a universal sodium dose and forced drinking; a sodium-containing product does not make excess fluid safe or guarantee cramp prevention.
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