The Passive Cycle Isolation System (PCIS) evolved from the lessons learned from EVIS. PCIS hardware worked by allowing the ergometer to free-float using low force isolators connected to the Orbiter.
PCIS consisted of four isolators that were installed between the CE mounting frame and the Orbiter floor. The isolators were of a much simpler construction than the EVIS isolators used previously. Each isolator was composed of wire rope wound into several loops to form a sphere of about five inches in diameter. During exercise, the isolators responded independently to the motion of the crewmember, allowing the system to rock back and forth. Each isolator experienced the full spectrum of disturbances, including torque, translation, compression, and extension forces. The restoring force produced by the isolator was a function of the stiffness of the wire loops comprising the sphere. The wire ropes essentially functioned as both springs and dampers, isolating the motion of the ergometer and acting as energy absorbers by bleeding off a small amount of energy.
The PCIS was first flown through DTO 682 on STS-62 in February, 1994. Although the isolators performed as expected to reduce loads transmitted to the spacecraft, it was also seen that additional stabilization was required for effective exercise.