Michael is a 17-year-old high school football player who has recently been doing "two a day" practices in preparation for the upcoming season. He is in good physical condition at 70 inches and 165 pounds. He is attempting to gain weight, so he has increased his intake of protein foods and estimates he eats approximately 3500 kcalories a day. One particularly hot afternoon, Michael is sweating profusely and begins to feel weak and has a difficult time keeping up with his usual practice routines. Noticing that his face is visibly flushed, his coach has him sit out of practice. Michael reports having eaten two peanut butter and jelly sandwiches, potato chips, and a can of soda for lunch, about 2 hours before practice. He had a breakfast burrito with eggs and cheese for breakfast with a 12-ounce glass of orange juice. 1. Which is typically one of the early symptoms of dehydration?