Arm movement Sensing

Hello, i need help to figure out how to sense a specific arm movement. I have two accelereometers and a flex sensor to measure every other arm movement, but i am stuck on one. If you put your fist by your chest and move your arm out, how would you sense that motion. it has to sense your arm going out and coming in with still a lightweight design. Here is a quick picture i made in paint showing what i have so far:

Also attached if you cannot see.

I am making an arm that mimics your arm movements. I have every motion except this one down... Anything will help!

Thank You, Easton

arm.jpg

Isn't this a cross-post? Please no cross posting in these forums.