Researchers at the University of Southern California and the University of Gothenburg in Sweden have found that male adolescents who had strong cardio fitness scored better in IQ tests—and wound up with higher education and income later in life. The scientists studied 1.2 million Swedish young men who were born between 1950 and 1976, and participated in mandatory military service at 18. They found that the more aerobic fitness the males had, the better their cognitive functioning—including verbal, mechanical, and logic skills. What’s more, the the boys who were most fit at 18 were most likely to go to post-secondary school. The researchers’ conclusion: Aerobic exercise improves mental ability because of the circulatory system’s effect on brain plasticity. (They did not study how muscle strength impacts intelligence.) They believe this study, which is published in the Dec. 8 issue of the Proceedings of the National Academy of Sciences, makes the case for more physical education programs in school.