PPT Slide
Muscles can only pull so in this example, the Biceps Brachii is creating a Flexor Moment/Torque.
The elbow can Flex or Extend
If the Muscle Moment/ Torque are both flexion then the muscle is contracting Concentrically.
If the Muscle Moment / Torque are opposite. A flexion Muscle Moment/Torque and the joint is Extending then the muscle is contracting Eccentrically.