Since each individual has a different body composition (i.e., bodyfat content, lean body mass), the answer to this question obviously varies from person to person. In addition, multiple factors affect your hydration status: climate, activity level, sweat rate, and your body size. The percentage of water within our bodies varies from 55% to 75% of total bodyweight. Your blood and muscle tissue consists of 83% and 75% water, respectively. Ideally, you should get about a third of your water intake from foods (fruits and vegetables have a relatively high water content) and the remaining from fluids. This means you should be drinking at least 1.5 to 4L of liquid daily. An easy way to determine that you're drinking enough fluids is to look at the color of your urine. Yes, that's right. Check to see that your urine is faintly yellow or almost clear. If this is the case, then you're drinking adequate fluids. If your urine is dark yellowish or orange and looks like concentrated apple juice, then consider yourself already dehydrated. Get some fluid into your body as quickly as possible.
Water loss can affect your body in many adverse ways. It takes only 1 to 2% water loss to negatively affect your aerobic endurance. Unfortunately, your thirst mechanism is not triggered until this amount of water loss has already occurred. 3% water loss may reduce your anaerobic endurance. Your muscle strength will be reduced at 4% water loss. 5% water loss will result in heat exhaustion, muscle cramps, fatigue, decreased blood pressure, and increased heart rate. Heat stroke and possible coma may result when 6% water loss occurs. 10 to 20% water loss will cause death.
You should drink liquid (preferably water) almost every hour throughout the day because a sufficiently hydrated body is a happy body. Plus, and this is very important, staying hydrated allows you to have more energy due to the increased circulation of nutrients (e.g., glucose, amino acids, fatty acids) within your blood stream. Waiting to drink water by the time you get to the gym is too late. You need to drink water regularly at least four to six hours prior to your workout to feel energized and ready to take on those weights. In the event you did not hydrate in advance before your workout, simply drink ice water instead. The cold water allows for quicker emptying from your stomach and thus increases rehydration rate--ideal before, during or immediately after training.
The dangers of dehydration are very real, especially as we get older. This is because the older we get, the less efficient our body's thermoregulatory mechanism becomes. Translation: we don't readily recognize the feelings of thirst as we age and losing more than 10% of body weight in fluid can be fatal. Dehydration can cause a whole host of problems including the following:
Before your workout, you should drink about 500 ml of water. During your workout, you should drink about 250 ml of water per every 15 minutes. Ideally, you should drink 16 ounces (2 cups) of water for each pound of bodyweight lost during exercise. Remember that exercising in a hot, humid environment means more sweating which means a faster rate of dehydration (i.e., it may only take 30 minutes before dehydration has occurred). Dehydration can readily occur in cold weather conditions as well because of water lost from breathing, sweating and increased urine production. Cold temperatures may decrease the thirst mechanism so you're likely to drink less. When drinking water to replenish lost amounts, you should aim to drink only 16 ounces in 15-minute intervals in order to allow the body time to absorb the fluid. By the way, the Center for Science in the Public Interest (CSPI) has found that nearly half of bottled waters comes from municipal sources and not from mountain streams as advertised on the labels. This means that tap water has as good a quality as most bottled waters for drinking.
Brian Danley, CFT
"Motivation is what gets you started. Habit is what keeps you going."
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I'm a personal trainer who loves to help others fulfill their health and fitness goals. I consider myself a bodybuilder in that I live the lifestyle of eating healthy food, working out regularly, and sculpting my body.