Six months in space does not have to weaken an astronaut’s heart, a new study says. Regular exercise protected cardiac function in orbit.

The research followed 13 astronauts on missions of about six months. It was published in the journal Circulation on September 15.

The paper, by Appadurai and Levine of UT Southwestern, found that structured exercise preserved the heart’s pumping ability.

In earlier missions, astronauts’ hearts shrank and weakened in weightlessness. The new results show the right training can prevent most of that decline.

The findings feed into planning for Mars missions. A trip to Mars would keep crews in low gravity for years.

Exercise devices on the International Space Station include treadmills, bikes and resistance machines. Future spacecraft will need compact versions.

The study compared heart measurements before, during and after the flights. The results suggest the right exercise prescription can protect the heart on long missions. Space agencies will use such findings to design training for future deep-space crews.