Another disconcerting finding is  that 10-year-old boys took an average of more than 10 minutes to run a mile and averaged fewer than 3 chin-ups. In Houston, about 50 percent of high school students scored “poor to weak” in the 600-yard run, an endurance test. More than one-third of third- and fourth-graders in low-income San Francisco schools were unable to do 10 minutes of moderate exercise. Finally, a study of elementary school children in Jackson County, Michigan, found that 98 percent showed at least one major risk factor for heart disease. Forty-two percent had high cholesterol levels; 28 percent had high blood pressure. In fact, more than half had at least three risk factors.