A new study from Kansas State University revealed that astronauts who spent a long-time in space may experience a decrease in their cardiovascular function resulting to a lower exercise capacity.

The study, published in the Journal of Applied Physiology, showed that prolonged space travel can decrease the ability of the heart and small blood vessels to transport oxygen to active muscles. Due to this, astronauts spending extended-time in microgravity could experience 30 to 50 percent reduction in their exercise capacity.

"It is a dramatic decrease," said Carl Ade, a kinesiologist at Kansas State University and lead author of the study, as per Gizmodo. When your cardiovascular function decreases, your aerobic exercise capacity goes down. You can't perform physically challenging activities anymore."

For the study, the researchers analyzed the data of nine male and female astronauts who spent around six months aboard the International Space Station. Before being sent to space missions, NASA performs various health measures to the astronauts to assess their physical fitness. These measures, which include cardiac output, oxygen uptake and hemoglobin concentration and saturation, determine how effective the person's heart and blood vessels in transporting oxygen to the muscles' mitochondria.

While aboard the ISS, the astronauts undergo moderate and high-intensity aerobic exercise on bicycle or treadmill for four to six days a week. On the other hand, NASA prescribed upper- and lower- body resistance exercise for six days per week.

A few days after returning the Earth, the astronauts were asked to repeat their aerobic exercise and resistance training. By comparing the two data sets, one from before space flight and the other after returning the Earth, the researchers observed a 30 to 50 percent decrease in astronauts' maximal oxygen uptake.

Maximum oxygen uptake is the standard measure of cardiorespiratory health. It is the maximum rate of oxygen consumed during exercise.

The astronauts' level of fitness was able to return above 97 percent of their previous levels 90 days after returning back to Earth. This shows that prolonged exposure to microgravity could have permanently affect cardiorespiratory health.