Introduction and ARED Background  This paper will discuss the design, development, and testing of the Advanced Resistive Exercise Device  for the International Space Station program. ARED is scheduled to fly on shuttle flight ULF2 and will be  located in Node 1 of ISS. ARED is a multi-format resistive exercise machine specifically designed for a  zero-gravity environment. Capable of 30 different exercises, ARED will be used daily by the astronauts  aboard the ISS to counter the loss of muscle and bone mass associated with long duration human space  missions. ARED is being developed at NASA’s Johnson Space Center in the Biomedical System Division.  The team consists of both civil servant and contractor engineers from many different organizations at  JSC. ARED has been developed specifically to improve the on-orbit resistive exercise capability,  reliability, and availability. The resistive force is generated by two, 200-mm (8-in) diameter dynamic  vacuum cylinders. A vacuum exists on one side of the piston and atmospheric pressure exists on the  other. The piston has a stroke of 30.5 cm (12 in) inside the cylinder. The cylinders are capable of  delivering a nearly constant load. In combination with various mechanisms, ARED provides a range of 0 -  272 kgf (0 - 600 Ibf) to the exerciser, which is important effective zero-g exercise. In addition, the flywheel  mechanism simulates the inertial force component of lifting free weights in a 1 -G environment. ARED thus  provides a more complete weightlifting experience than any previous on-orbit resistance exercise device.  It will allow astronauts to perform a wider variety of exercises at higher loads, higher speed, and longer  stroke which, in turn, will enable them to maintain their health more effectively in a zero-gravity  environment.  The need for ARED, arose out of reliability and performance concerns with previous resistance devices  for ISS. ARED is being designed, tested, and certified for a 15-year service life, which is much longer  than any previously designed device. This long service life is needed to support long duration space  missions, which will require a robust and reliable weightlifting machine. ARED’s predecessor, IRED, has a  0 - 136 kgf (0 - 300 Ibf) load range whereas ARED will enable the crew to exercise up to 272 kgf (600  Ibf). ARED will allow for a wide range of both bar exercises (squat, dead lift, heel raise, etc) and cable  exercises (hip abductors, one-arm curls, etc). The load and stroke capability for bar exercises is 0 - 272  kgf (0 - 600 Ibf) and a 76.2-cm (30-in) stroke. The load and stroke capability for cable exercises is 0 - 68  kgf (0 - 150 Ibf) and a 183-cm (72-in) stroke. ARED’s vacuum cylinders have a nearly constant loading  profile, which is more medically advantageous than the varying loading profile that is provided by springs  and rubber based exercise devices. In addition to providing more constant load than IRED, ARED  attempts to simulate the inertia that is felt during free-weight, 1 -G exercise by employing a flywheel that is  directly tied to the motion of the cylinders. The differences are shown in Table 1.  Table 1. Comparison chart of ARED vs. IRED  31 8