Muscle Cylinders in Osprey forearm

The muscle cylinders revealed by an open forearm panel of a ST-10 Osprey.

Muscle Cylinders are specialized pistons or linear bladders[1] that are the foundational components for movement in all mobile frames


At the core of the muscle cylinder technology is muscle cylinder fluid. Muscle cylinder fluid contracts and expands on its own according to electrical stimulus, and generates electrical stimulus when compressed or expanded.[2] While extremely useful due to these properties, muscle cylinder fluid is also violate and can explode if handled improperly or ignited in combat.[3]

Developed in the early years of colonial expansion by the Solar Union, muscle cylinder technology uses muscle cylinder fluid and an applied electrical current to create a controlled, piezoelectric phase shift to reduce and expand the cylinder in volume along its longest axis. In this way, the cylinder acts like a muscle, contracting or extending linearly to move a limb or other frame component.

Muscle cylinders can be utilized in unison by connecting them with wires. When arrayed this way across an entire frame, the muscle cylinder network functions as a nervous system for the frame and with training the network is capable of reacting to and almost anticipating the control inputs of frame operator. In addition to delivering signals to the muscle cylinders to extend or contract, this network is also capable relaying force feedback to the pilot which grants the operator a detailed and proportionate sense of the external environment.


Professional frame pilots run a new frame through a series of exercises to sync it to the pilot's inputs. Highly skilled pilots can imbue a frame with reactions of it own, such as maintaining balance and dodging maneuvers. The Terran Expeditionary Marines have perfected this training into the Sokokunst doctrine, a martial art form used throughout the colonies. Melee weapons are often used, including bladed weapons, batons and fusion edges.

When a damaged muscle cylinder is replaced, the new cylinder must be trained before it will work in unison with the older cylinders.[4]


Main Source: Mobile Frame Zero: Rapid Attack Rulebook