People who participate in tennis three hours per week at moderately vigorous intensity cut their risk of death in half from any cause, according to physician Ralph Paffenbarger of Harvard University School of Public Health. Paffenbarger not only studied over 10,000 people over a period of 20 years in his landmark ‘College Alumni Health Study’, but also finished over 150 marathons over the age of 45. Read more tennis benefits.