How sweat output scales from rest to hot-weather effort
Sweat rate spans a wide range depending on temperature, humidity, intensity, and the individual. At rest indoors in cool conditions, losses may be modest, on the order of a few tenths of a liter per hour. During hard exercise in hot outdoor conditions, sweat rates of roughly 1.5 to 2.5 liters per hour are common, and some large, fit athletes exceed that. These are approximate ranges, not fixed values, because body size and clothing matter as much as the thermometer.
The curve rises steeply once both heat load and exercise intensity climb together, since the body must dump a great deal of metabolic heat through evaporation.
How acclimatization reshapes the curve
A heat-adapted person sweats earlier and more, and their sweat is more dilute in sodium, which improves cooling while conserving salt. This shifts the relationship between temperature and effective heat loss favorably. The flip side is greater total fluid demand, so fluid and electrolyte planning becomes more important in the heat.
This is general educational information, not medical advice. Very high sweat losses can lead to dehydration or, if replaced with plain water alone, to low blood sodium; a qualified professional can advise on individual fluid strategies.