"Even with onboard exercise, astronauts face the risk of losing muscle mass and function because their muscles are not bearing enough weight, or load," said Dr. Vincent J. Caiozzo, investigator on NSBRI's Muscle Alterations and Atrophy Team. "For exploration, it is important to find ways to increase load-bearing activity so astronauts can maintain strength."

Caiozzo's team is researching whether squats executed under artificial gravity conditions greater than or equal to Earth gravity (1g) produce the same kind of muscle responses that occur when a person performs weight training on Earth.

With long-term initiatives like the International Space Station and the proposed lunar and Mars missions, the rate of muscle loss in some areas might rise to 25 percent unless measures are taken to confront atrophy. The loss of muscle strength during an extended mission could pose dramatic problems in the event of an emergency situation upon landing.

The Space Cycle, a human-powered centrifuge under testing in Caiozzo's lab, generates various levels of artificial gravity ranging from Earth gravity to five times Earth's gravity. The speed of rotation determines the level of gravitational force.

Participants ride opposite one another ¿ one on a bike and one on a platform. As one person pedals, the cycle moves in a circular motion around a centralized pole. The motion generates pressure on the rider, forcing him against the seat in a manner similar to the effect of gravity on Earth. On the platform, the other person performs squat exercises. Instruments on the device report the separate work rates of the participants.

Caiozzo's team is determining the Space Cycle's effectiveness by comparing the participants' pre- and post-study muscle mass and strength, muscle fiber cross-sections from biopsies, and various cellular and molecular markers of growth.

"The novelty of artificial gravity resistance training is that each element of the body is loaded proportionally. Leg muscles can be made to work against high loads without the need for external weights, which is important in light of the limited mass and space available on missions," said Caiozzo, professor in the Departments of Orthopaedic Surgery, Physiology and Biophysics at UC Irvine.

In collaboration with Caiozzo, UC Irvine researchers Dr. Joyce Keyak and Dr. Jim Hicks are gathering data from the participants to determine whether the Space Cycle is also effective in maintaining bone mass and cardiovascular fitness.

"Space Cycle is an artificial gravity exercise gym," Caiozzo said. "The platform can be fitted with a treadmill, bike or any kind of exercise equipment and provides an environment for exercise under normal, Earth-like loading conditions."

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