**7.2 Why artificial gravity with exercise**

Although a short-radius centrifuge has been proposed several times, loading with artificial gravity has not been demonstrated to be effective at preventing spaceflight deconditioning on its own. Making a human-powered short-arm centrifuge is an effective method to create exercise loads for astronauts. Considering the size of the ISS, it is appropriate to employ a short-radius centrifuge rather than a large-radius human centrifuge; however, it may be beneficial to rotate the spacecraft itself to provide the artificial gravity for long-duration spaceflight such as Mars expeditions.

In 1999, Iwase proposed the creation of artificial gravity by ergometric exercise, and it was installed at Nagoya University [33]. Several studies were performed using this short-radius centrifuge with an ergometer. In 2002, a bedrest study was carried out to evaluate the effectiveness of artificial gravity with ergometric exercise. In 2005, the facility was moved to Aichi Medical University, and bedrest studies

#### **Figure 1.**

*Structure of the device of artificial gravity with exercise for AGREE project 2012.*

were performed to finalize the protocol. This daily AG-EX step-up protocol was confirmed to be effective at preventing cardiovascular, musculoskeletal, and bone metabolism deconditioning in 2006, whereas the alternate-day (every-other-day) protocol (loading the AG-EX every other day) did not improve the spaceflight deconditioning associated with the microgravity exposure analogue of −6° headdown bedrest.

The authors applied for the installation of a short-radius centrifuge facility on the ISS and proposed it as a method to prevent spaceflight deconditioning, including bone loss. This project, Artificial Gravity with Ergometric Exercise (AGREE project), was promising to prevent space deconditioning during spaceflight, but it was canceled halfway through (**Figure 1**).
