So, to clear up confusion, there are now exercise guidelines for cancer survivors.
When Marty Alertman was diagnosed with breast cancer fifteen years ago, just did what she always does - turned to exercise to help.
"It helps me get through my day. I am a very high-anxiety person, and exercise really levels me off," she said.
Because there are now an estimated 12 million cancer survivors like Marty, the American College of Sports Medicine released new exercise guidelines for this population.
"These guidelines cover that cancer continuum. They're safe for people undergoing treatment, they're safe for people who have finished their treatment and are moving beyond that cancer," said Colleen Doyle of the American Cancer Society.
The guidelines are consistent with those for the general public - moderate to vigorous activity for 150 minutes per week. Even fast-paced walking counts.
But for some there are precautions. Depending on the treatment and the site of the cancer, some patients will have to slow down or cut back.
"I always encourage people, don't push yourself. If you don't feel like it on a particular day, don't worry about it, see how you feel the next day," said Doyle.
But the main takeaway is to avoid inactivity. It's advice Marty understands.
"When I run, no matter what's going on, I feel better," she said.
The guidelines also include recommendations for what to during chemotherapy versus radiation. Plus, the report shows how exercise can help with certain side effects.