PALO ALTO, CA – Dr. Ralph S. Paffenbarger Jr., a medical professor and researcher whose study of the connection between exercise and longevity impacted the modern physical fitness movement, has died. He was 84.

Paffenbarger, a former Harvard professor and a researcher at the Stanford University School of Medicine, died July 9 at his home in Santa Fe, NM, after a long battle with congestive heart disease, Stanford University announced.

The noted epidemiologist spent several decades studying the exercise levels, illnesses and deaths of more than 50,000 people who had graduated from either Harvard or the University of Pennsylvania between 1916 and 1950. In his study published in 1986, Paffenbarger showed that men who burned at least 2,000 calories a week—the equivalent of jogging or walking briskly for 20 miles—had death rates one-quarter to one-third lower than those who did not exercise regularly. The study also showed that the amount of additional life for people who got adequate exercise, compared to those who did not, was one to two years.

Paffenbarger took up running in 1967 at age 45 and kept running until heart problems forced him to give it up in 1993. He then favored walking as his form of exercise. Paffenbarger told the Chicago Tribune in 2000 that most of the men in his family had died in their 50s of heart disease, and that his own longevity surprised him.

In 1996, Paffenbarger was a recipient of the first International Olympic Committee prize for sport science. According to Stanford University, his work influenced the 1996 Surgeon General’s Report on Physical Activity and Health, as well as exercise guidelines issued by the American College of Sports Medicine and the Centers for Disease Control and Prevention.