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Beat Summer Fatigue: Fluids and Electrolytes for Sweating Smart
Hello, this is Kitamura, the owner of Orange Fitness in Kai City, Yamanashi.
When the rainy season ends, temperatures jump as if someone flipped a sauna switch.
“I came to the gym and nearly gave up during the first warm-up.”
“I’m dripping with sweat, but for some reason I’m not thirsty.”
I get more questions like these every year at this time. Most of the time the cause is not simply the heat. It is a breakdown in the balance of water and electrolytes. So this time I’ve put together the tips I give members for “sweating smart,” with the reasoning and practical examples.
Why summer wears you out so fast
Our bodies control temperature through sweating: sweat evaporates and the heat of evaporation cools us. But sweat contains not just water but plenty of electrolytes such as sodium and potassium. If you replace it with water alone, your blood is diluted and you fall into “hidden dehydration” with fatigue, headaches and nausea. In fact, many people who collapse in the heat do so from “too little salt plus too much water” rather than from the heat itself.
The guide is “body weight × 35 mL” plus exercise: are you getting enough?
The guideline from Japan’s Ministry of Health, Labour and Welfare is 35 mL per kg of body weight. For someone who weighs 60 kg, that is about 2.1 L at rest. If you also “sweat properly for 30 minutes at the gym,” you need an extra 500–600 mL. Even if you think “I drink a 2-liter bottle a day, so I’m fine,” you’re probably short on days you exercise. Knowing your fluids and salt “in numbers” is the first step to avoiding summer fatigue.
Drinking has its “timing and contents” too
Points
- A sports drink with 4–8% sugar is “isotonic” and absorbed efficiently
- Gulping cold water shocks your stomach. Room temperature to slightly cool is better
A daily timing table
| When | What and how much? | Purpose |
|---|---|---|
| Right after waking | 200 mL of room-temperature water | Resets dehydration from sleep |
| 30 minutes before training | 250 mL of water plus one salt tablet | “Pre-loads” the salt you’ll lose in sweat |
| During training | 100 mL of sports drink every 10–15 minutes | Guards against dehydration and low blood sugar together |
| Within 10 minutes after training | 300 mL of oral rehydration solution | 40 mg or more of sodium per 100 mL for the fastest recovery |
| 1 hour before bed | 150 mL of caffeine-free barley tea | Replenishes potassium and supports deep sleep |
Three electrolyte “chargers” you can buy at a convenience store
- Oral rehydration solution (OS-1 or Aqua Solita): rooted in dehydration care in hospitals. Ideal after outdoor work in midsummer or after a sauna.
- Salt-charge tablets plus natural water: one tablet is about 300 mg of sodium. A good choice if you prefer less sweetness.
- Unsweetened sparkling water plus a pinch of natural salt: a great-value homemade hypotonic drink. Adding lemon juice speeds up recovery from fatigue.
Frequently asked questions
Q1: I feel puffy when I drink a lot of water.
A1: If you add water without enough salt, your body holds on to water to restore the diluted salt concentration. Always pair water with salt.
Q2: Do coffee and green tea count as fluids?
A2: They do, but caffeine promotes urination. After one cup of coffee, add the same amount of water to come out ahead.
Q3: Can I get too much salt from salt tablets?
A3: In 30 minutes of cardio you sweat 300–400 mL and lose about 240 mg of sodium. One or two tablets won’t be too much. On days you prefer strong flavors, take a little less.
“Sweat smart” rules to start today
- After waking, before training and after training: just these three times, always take water and salt together.
- Alternate your bottle between “flavored, water, flavored, water” so you don’t get bored.
- If your weight is down 1% or more after training, that is a sign you didn’t replace enough.
Follow these three and you can shift from a body that “drinks and still wilts” to one that “drinks and keeps moving.” Peak summer is almost here. Today, add the small step of “electrolytes” to your bottle. How you feel after a workout will change.
Orange Fitness is a semi-personal gym in Kai City, Yamanashi. Learn how coaching works, see our plans and pricing, or book a trial or tour. You are welcome to just look around.