Over 50s who regularly exercise were found to have had more lovers during their lives than their less active peers, according to a study published in journal BMJ Sexual & Reproductive Health.
A significant association between exercise and sexual partners was not seen among men.
The study included data from almost 7,000 men and women over the age of 50 in England.
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Men were more likely to report a higher number of lifetime sexual partners than women, the researchers found.
One in five men (19.9%) and one in 10 women (8.5%) reported having had relations with more than 10 people.
Almost two in five men (39.7%) said they had had at least five previous sexual partners, compared to around a quarter (24.1%) of women.
Among women over the age of 50, bisexuality, being white and not having had a long-standing illness were also each independently linked with having a greater number of previous sexual partners, compared to those who did not have the characteristic.
Among men, a link was found between a high number of previous partners and homosexuality, as well as being among the most and least wealthy.
"This information may help health practitioners to identify individuals who are at greatest risk of STIs and their associated health complications across the life course," the authors wrote.
"Moreover, findings from the present study could also benefit younger adults through targeted interventions to educate groups at risk of having a high number of sexual partners about the risks associated with doing so, and the practice of safe sex."
The study was carried out by an international team of researchers from institutions including UCL and Anglia Ruskin University.