Washington, Feb 15 (IANS): Astronauts on the International Space Station (ISS) are not only working out to keep their hearts healthy but also to generate data to advance knowledge of health and fitness on Earth, a NASA research indicates.

Researchers assessed exercise on longer spaceflights with the help of astronauts on the space station, measuring their oxygen consumption peak VO2 before, during and after missions of four to five months.

Widely accepted as the best measure of cardiovascular fitness, VO2peak, also called VO2max, is a measure of peak oxygen uptake.

That represents the highest amount of oxygen your body can use to produce energy during exercise.

"Oxygen is used by cells to provide the energy to perform work and a more aerobically fit individual's cells take up and use more oxygen," said Meghan Downs, senior researcher at NASA's Exercise Physiology Laboratory in the US.

The results showed that VO2peak decreased by an average of 17 percent by day 15 in space, but then gradually increased.

Most astronauts never recovered their pre-flight V02peak levels during the mission but a few were able to maintain or even improve VO2peak during flight with frequent bouts of high-intensity exercise.

Currently, each crew member is prescribed a two-hour daily workout using three pieces of equipment on the station.

The data would also help predict what activities an astronaut should be able to tolerate after a long spaceflight. This would help in planning future missions.

Astronauts with higher VO2peak levels, for example, would be better able to work in heavy spacesuits exploring an asteroid or walking around Mars.

The results was published in the Journal of Applied Physiology.