Exercise keeps 14 astronauts' hearts within Mars-tolerable range, station echocardiograms show

All fourteen astronauts exercised. Each began the station's standard routine as soon as they were able, roughly 45 minutes to an hour a day of endurance and strength work ^[14]. There is no unexercised group in the study ^[26], so the untreated comparison is the older literature. "Our previous studies had demonstrated that the heart atrophies in both bed rest and in space," said Benjamin Levine, professor of internal medicine in UT Southwestern's Division of Cardiology ^[3][4].

Taken across about 180 days, 45 to 60 minutes daily comes to roughly 135 to 180 hours of exercise per crew member ^[21]. The routine was the programming already standard on the International Space Station ^[14].

Before launch, each astronaut was scanned in three positions: lying flat for zero gravity, at a 22% tilt for something close to Mars, and sitting upright for Earth ^[11]. Mars' gravity is about 3/8 of Earth's ^[13], or about 0.375 g ^[20].

In orbit the scans came at about days 14, 30, 75 and 135, then once more 15 days before landing ^[12]. Five sessions, three of them inside the first 75 days ^[23]. On a roughly 180-day mission the last one falls near day 165, about a month after the day-135 scan ^[22].

Levine said the early change was not surprising, because most astronauts experience some motion sickness ^[16]. The paper does not report the electrical activity the Integrated Cardiovascular Study also set out to characterize ^[5]; echocardiography with Doppler measured the heart's anatomy and how efficiently it pumped blood ^[9].

Levine worked on this phase with Michael Bungo of the McGovern Medical School at UTHealth Houston and James Thomas of the Northwestern University Feinberg School of Medicine ^[6]. "Our findings suggest that the exercise countermeasures we already have in place are enough to keep the heart in good working order for Mars' gravitational loads," Levine said ^[2].