You finish a morning run around the park, you're drenched, and you down two big glasses of water. Job done, right? Not quite. If you've ever felt strangely flat, headachy, or crampy after a workout despite drinking plenty of fluids, there could be several reasons, including heat, tiredness and your fluid and salt balance. Plain water, on its own, may not always be the full answer after long, sweaty sessions.
Here's the thing most people miss — sweat isn't pure water. Every time you sweat, your body loses a mix of water and electrolytes. Electrolytes are minerals that carry an electrical charge and help keep everything from your muscles to your heart working properly. The main ones lost through sweat are sodium and chloride, with smaller amounts of others such as potassium and magnesium.
In a hot, humid climate like Singapore or Malaysia, you are likely to sweat a lot. You're often sweating before your workout even begins. During longer or harder sessions, the sodium and chloride you lose can add up, and sports nutrition reviews suggest these may need replacing along with the water.
Sodium is the electrolyte you lose most of when you sweat. It plays a central role in fluid balance — it helps regulate how much water sits in and around your cells. Drinking very large amounts of plain water, especially during long endurance events, can dilute the sodium in your blood, a condition called hyponatraemia. In mild cases it may cause symptoms such as fatigue and nausea. In severe cases it can become dangerous.
Ever got a cramp mid-run or right after? It's tempting to blame dehydration alone, but the real cause of exercise cramps isn't fully settled. Fluid and electrolyte loss may play a part, and many researchers also point to muscle fatigue as a major factor. Magnesium and potassium both help control how your muscle fibres contract and relax, and a true shortage of either can affect the muscles, though a normal sweaty workout hasn't been shown to cause that.
Magnesium also plays a role in energy production in the body. Still, that afternoon slump after a morning hawker run in the heat can feel brutal for many reasons, including the heat itself, tiredness and how much you've eaten.
Potassium supports normal heart rhythm and nerve signalling. Very low potassium can cause weakness and affect the heart's rhythm, although this is usually linked to medical conditions rather than an ordinary workout. Dizziness or a general feeling of weakness after sweating has many possible causes. This isn't just an athlete problem. Anyone doing brisk walking, a weekend cycling session, or even a long time walking around a shopping mall in the humidity can lose fluid and some salts through sweat.
This sounds counterintuitive, but hear it out. Research on rehydration suggests that sodium helps your body hold on to the fluid you drink, while plain water alone is regained more slowly and may lead to more urine being passed. Drinking only plain water after a long, heavy sweat may therefore not rehydrate you as well as a drink or meal that also contains some sodium.
General hydration guidance still treats water as the main drink, and for most people thirst is a good guide. But sports nutrition reviews suggest that for sessions lasting about an hour or more, or in very heavy sweating, replacing sodium and other electrolytes alongside fluids can matter. This is especially relevant if you're active for long stretches, or if you're doing anything outdoors during the hottest part of the day in Singapore.
Hard exercise increases the production of free radicals (unstable molecules that can damage cells), and working hard in the heat may add to this. Vitamin C acts as an antioxidant that helps neutralise these molecules, although research on whether extra vitamin C helps exercise recovery is mixed. Zinc contributes to normal immune function, which is one reason it gets attention in sports nutrition.
These aren't the main things lost in sweat, but supporting your body's recovery processes after a tough session in the heat is part of the full picture.
You don't need to overthink this. The key principles are simple:
The kiasu instinct to optimise everything doesn't have to stop at macros and step counts. Understanding what your sweat is actually costing you is a practical way to think about how you feel and perform — especially when you're training in one of the hottest and most humid regions on the planet.
This article is for general informational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional before making changes to your diet, supplementation, or exercise routine. Individual needs vary.
Ask Elaine how this applies to your goals and routine — free, no pressure.