Shuttle experiment. Mission specialist Steven A. Hawley performing a treadmill experiment on space shuttle mission STS-93. This mission, on the space shuttle Columbia, took place between 23rd-27th July 1999. This experiment was designed to assess the Treadmill Vibration Isolation and Stabilisation (TVIS) system. The treadmill's movements should not interfere with other on-board experiments. If this is the case, the TVIS system will be used for exercise on board the International Space Station. Exercise is important in the microgravity encountered in orbit as muscles may atrophy (waste away) if they do not have to work against Earth's gravity.