check out Sparkfun for their sensors as well...
from what it sounds, you want a sensor to "sense" what the body is trying to do
and then amplify the strength of that body part by using servos, motors, air muscles,
etc to increase the output force...
if you're taking an arm, then I recommend accelerometer to measure the angle of the
arm, gyro to measure the rate of change... you could also use gyro to make your
accelerometer more precise because accelerometer gets noisy reading if the device is
in motion... you could use force sensor inside the armor suit to measure the amount of
force the body is pressing against the wall of your suit...
for motors you could use servos... they have high torque digital servos... you could also
use gearmotors for some more torque... you could try using cylinder pumps or air muscle
composed of hoselike tubing that is pumped with compressed air, etc... are u gonna
make a mechwarrior?.. =)