Unit 1
A coaches B participated C weight D extra E drinks F slower G functions H health I athletes J abnormally
After years of telling athletes to drink as much as possible to avoid dehydration（脱水）, some doctors are now saying that drinking too much during intense exercise presents a far greater 1 risk, according to a report in The New England Journal of Medicine.
An increasing number of 2 ---marathon runners, and even hikers--- are severely diluting（稀释） their blood by drinking too much water or too much sports 3 . A new research involved 488 runners who 4 in the 2002 Boston Marathon. While most were fine, 13 percent drank so much that they had 5 low blood sodium（钠）levels. Three had levels so low that they were in danger of dying.
The runners who developed the problem tended to be 6 , taking more than four hours to finish the course. That gave them plenty of time to have large amounts of liquid. And they did so much drinking that they actually gained 7 during the race. During intense exercise the kidneys cannot excrete（排泄）excess water. But as people keep drinking, the 8 water moves into their cells, including brain cells. The brain cells, with no room to expand, press against the skull and can compress the brain stem（脑干）, which controls vital 9 like breathing. The result can be fatal.
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