I finally have a full assembly of all the major components sewn with thick canvas and leather. The small scuba tank provides the air pressure, controlled by an Arduino and solenoid valves. The basic operation of pneumatic muscle works. Air pressure at about 100psi inflates the muscle, creating a contracting motion of about 2 inches, enough to make my leg kick out (although the speed of inflation needs to be faster).
The harness for the scuba tank and a guide for the pneumatic muscle are still issues to be dealt with. The strap for the thigh needs to extend further down to help guide the placement of the pneumatic muscle and the scuba tank needs to be attached in a more comfortable way.