A myograph is any device used to measure the force produced by a muscle when under contraction. Such a device is commonly used in myography, the study of the velocity and intensity of muscular contraction.
A myograph can take several forms: for tubular structures such as blood vessels these include the pressure myograph (where a segment of a blood vessel is cannulated at either or both ends) and the wire myograph (where the blood vessel segment is threaded onto a pair of pins or wires); for skeletal muscle other devices such as the acceleromyograph can be used.
References
Myograph Wikipedia(Text) CC BY-SA