While exercise has been found to benefit cancer patients both physically and psychologically, researchers say a new study proves it can also boost the effect chemotherapy has on a patient.

In a study by a team at the University of Pennsylvania, researchers using a mouse model of melanoma found that combining exercise with chemotherapy shrunk tumors more than chemotherapy alone.

The researchers sought to find whether exercise would protect against negative cardiac-related side effects of the cancer drug doxorubicin, which is known to damage heart cells.

The team first injected melanoma cells into four teams of mice. They then injected two groups with doxorubicin and the other two with a placebo. Over a two-week period mice in one of the groups injected with the drug and one of the untreated groups walked 45 minutes, five days a week, on treadmills, while the other two groups did not.

While data showed that exercise did not help protect against cardiovascular damage, it did show that in mice that had received the drug and exercised, tumors significantly shrunk.

“We looked, and the exercise didn’t do anything to the heart – it didn’t worsen it, it didn’t help it,” Joseph Libonati, senior author of the study and associate professor at Penn School of Nursing, said in a news release. “But the tumor data – I find them actually amazing.”

The team plans to examine further how exercise enhances the effect doxorubicin has on tumors, but are encouraged that results may help find ways to cut down on cardiovascular damage caused by the drug.

“If exercise helps in this way, you could potentially use a smaller dose of the drug and get fewer side effects,” Libonati said.