WHAT ARE YOUR THOUGHTS ON SWEAT TESTS ?

Q: I recently did a sweat test, and the results suggest I need 1,000 mg or more of sodium per hour during workouts and races. What are your thoughts?

A: A sweat test can provide some information, but at Hammer Nutrition we place limited value on these tests because they measure only a narrow set of variables and may not reflect what happens during prolonged exercise. In simple terms, the results from a short, controlled sweat test are not necessarily representative of sodium and fluid losses over several hours.

In a typical sweat test, an athlete runs on a treadmill or rides a stationary bike in a controlled setting, with sweat collected to estimate fluid and electrolyte loss. This can describe sweat rate and sodium loss for the period tested. However, these tests are often about an hour long. Data from that first hour may not predict losses in later hours of longer sessions.

The article’s position is that fluid and electrolyte losses are often higher early in exercise, particularly in the first 30–60 minutes. A common mistake is to assume the rate and amount of sodium loss measured in that early period will continue unchanged hour after hour. This approach does not account for the body’s regulatory systems that influence fluid and electrolyte balance during extended exercise.

The article notes that the body begins exercise with substantial amounts of sodium already present. As exercise starts, some sodium and fluid are typically lost. In response, hormonal regulation becomes more active to help manage ongoing losses.

Aldosterone and sodium conservation 

The article describes aldosterone as a hormone involved in monitoring sodium levels and helping conserve sodium. When sodium losses become high, aldosterone promotes processes in the kidneys that recirculate sodium back into the body, reducing further sodium loss. The article states that this process does not cover requirements indefinitely and that electrolyte supplementation can still be useful to support adequate electrolyte status during prolonged exercise.

Why the article cautions against matching sweat test numbers

The article argues that many athletes over-consume sodium after seeing sweat test results indicating losses of 1–2 grams of sodium. It notes that 1–2 grams of sodium is equivalent to 2.5–5.0 grams of salt (because salt is approximately 40% sodium and 60% chloride). The article states that consuming 1–2 grams of sodium per hour is typically excessive.

It further states that when the body detects high sodium intake from external sources (food, salt tablets, or high-sodium products), aldosterone signalling changes and the kidneys reduce recirculation of sodium. The article claims the body may then excrete more sodium than before.

Possible effects of excess sodium intake

The article states that when aldosterone’s normal action is reduced due to high sodium intake, vasopressin may become more influential, contributing to fluid retention. It describes this as swelling (oedema) in the extremities. It also lists other potential consequences of excessive sodium intake, including increased blood pressure, increased sodium excretion, and increased fluid retention, which it presents as both performance-inhibiting and potentially harmful to health.

It suggests that signs of excessive sodium intake may include:

• swollen hands, wrists, feet, or ankles after exercise
• puffiness under the eyes or around the cheeks
• excessive salt staining on skin or clothing

Bottom line

The article’s conclusion is that consuming too much sodium/salt — in the daily diet, prior to exercise (sodium loading), or during exercise — can be more harmful than helpful. It adds that excess intake of water, sodium, calories, and other inputs can lead to problems ranging from stomach distress to more serious outcomes such as hyponatraemia.

It repeats the view that sweat tests may provide limited useful information but should not be used to set an hourly sodium replacement target that matches measured losses. The article argues that attempting to replace sodium in equal amounts to sweat test estimates can lead to negative outcomes, including impaired performance.