By Dimity McDowell and Randi Bernfeld; Photography by Freepik
Forget eight glasses a day. When you’re working out, rules of thumb go out the window. Here’s exactly how much water you need when you exercise.
You know that feeling when you’re halfway through your high-intensity class and suddenly you feel light-headed, weak and as desperate for a sip of water as if you were crawling through a desert? That’s called dehydration and it’s not a good thing – for your body or your workout. Water is a multitasker: Among other things, it lubes your muscles, transports nutrients around your system and shuttles waste out of it, allowing your kidneys to function smoothly.
Every sweat bead on your skin equals less water in your system. When you’ve sweated out 1 percent of your body weight, two things happen (and continue to happen with every additional 1 percent lost): Your heart rate rises 7 beats per minute in order to push your thickening blood through your body and your core temperature increases a little. Lose 2 percent (totally doable in an hour if you’re pushing hard) and not only are you physically suffering (your pace slows), but your brain starts going funny – it’s 80 percent water, so it short-circuits at the first sign of a drought. Your reaction times become longer and you have trouble finessing certain tasks, like agility drills. Dry out even more, and you may get headaches, cramps, and dizziness as your body loses its ability to transport blood as efficiently.
Work Out Your Water Needs
As a rule, the more active you are, the more water you need. And while the recommendations are nowhere near one-size-fits-all, they boil down to this: Start your workout with a full tank, then replenish your fluids based on your pre- and post-workout weight. You can calculate roughly how much your body needs by following this plan:
4 hours before you go-time: Drink a cup and a half of fluid, then weigh yourself. If your pee is the shade of apple juice or darker, plan to gulp another cup or two 2 hours before you exercise.
During your workout: Replenish with half a cup every 15 minutes. Drink more if you’re working out at a high intensity for longer than an hour.
Post workout: Weigh yourself again. Drink two cups per 500 grams you’ve lost. If you gained weight, you’re drinking too much.
Skip The Down-Downs
Regardless of what’s in your water bottle, resist the urge to gulp it all down the instant your workout ends. In fact, sip no more than two cups an hour. If you try to drink more than that after exercise, you’ll be lulled into a false sense of security. Your system can’t process water that quickly, so while your pee may be clear, your body still may not be hydrated. If you plan to exercise twice in one day, the American College of Sports Medicine recommends drinking about two and a half to three cups for every 500 grams of weight lost to compensate for the extra urine you’ll produce. But for your average day with one hour-long gym session, drinking two cups per 500 grams lost over the day is sufficient.
Match Your Water To Your Workout
After a killer workout, we say things like “I’m sweating like a pig.” Sick of such vague comparisons, we contacted research physiologist Dr. Samuel Cheuvront to find out how much average 60-kilogram woman actually sweats during various activities.
Cleaning the house for an hour
You burn: 700kJ Drink: Half a cup of water
Strength training for 30 minutes
You burn: 700kJ Drink: 1 cup
Swimming for 45 minutes
You burn: 1 760kJ Drink: A cup and a half
Road running for eight kays
You burn: 1 950kJ Drink: Three cups
Spinning for half an hour
You burn: 2 100kJ Drink: Four cups
*Calculations are approximations based on standard exercise intensity, energy burn, clothing, and room and air temperatures. Individual needs vary.
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