Another example is the dumbbell curl at the elbow. The "elbow flexor '' group is the agonist, shortening during the lifting phase (elbow flexion). During the lowering phase the "elbow flexor '' muscles lengthen, remaining the agonists because they are controlling the load and the movement (elbow extension). For both the lifting and lowering phase, the "elbow extensor '' muscles are the antagonists (see below). They lengthen during the dumbbell lifting phase and shorten during the dumbbell lowering phase. Here it is important to understand that it is common practice to give a name to a muscle group (e.g. elbow flexors) based on the joint action they produce during a shortening (concentric) contraction. However, this naming convention does not mean they are only agonists during shortening. This term typically describes the function of skeletal muscles.
which muscle/muscle group would be the prime mover for an arm curl
elbow flexor elbow flexor elbow flexor elbow extensor