Fluid is a crucial component of endurance training. As little as one percent of fluid loss can be detrimental to your performance. Between 50-60 percent of our total body mass is made up of water, and 70-75 percent of our muscles comprise of water. Fluids, specifically water, is the main component of blood. Blood transports nutrients and oxygen to our cells. Muscle glycogen also holds a large amount of water, and the water helps remove lactic acid from exercising muscles. Fluids act as shock absorbers in the joints and around the brain and spinal cord, lubricate the digestive tract.
At rest, urine excretion represents the greatest amount of fluid loss, however, during exercise our greatest loss is through sweating. Fluids also aid in the temperature regulation of our bodies. As our body temperature heats up during exercise, we sweat to cool our bodies. The warmer our bodies get, the more we sweat. The more we sweat, the more fluid we lose. Sweating during training can result in a fluid loss, especially for an endurance athlete. Exercising in warm or humid weather, dry climate, or at altitude can increase fluid loss. Anywhere from 16-48 ounces of sweat an hour can be lost during training. Blood volume decreases while sweating, placing greater demands on your cardiovascular system. This reduces your ability to use oxygen. When fluid loss is not replaced, your body temperature increases and exercise becomes harder.
It is essential that your drink a minimum of 8-10 cups of fluid for normal functioning. During each hour of exercising you should be drinking at least 16 ounces. To ensure adequate hydration during exercise, drink 24 ounces of fluid two hours before exercise, and 8-16 ounces 30 minutes before exercise. About half of your fluid intake should be water, but you can also hydrate yourself by drinking non-caffeinated beverages. You can drink caffeine in moderate amounts, but you need to be careful that you don't overdo it. Caffeine acts as a diuretic, increasing urine excretion, which can lead to dehydration. Excess caffeine can also interrupt your sleep patterns.
As you can see, fluids are a key element during your training. Unfortunately, being thirsty is not a good indicator of how much fluid your body requires. Some early signs of dehydration are tiredness, headaches, dark colored urine, and increased heart rate. Fluid intake should be monitored throughout the day, not just during training, for endurance athletes. Not meeting your fluid needs can greatly damage your performance. During your training, experiment with different amounts and kinds of fluid. Pay attention to what makes you feel "good" during your workout. This will tell you what and when you need to drink during race day.