a. The elbow flexors are the agonists and elbow extensors the antagonists is a false statement. This exercise involves forceful concentric elbow extension during the pushing phase, and eccentric action by the same muscles in returning to the start position. The antagonist elbow flexors (biceps brachii and others) are inhibited or relaxed so they don't oppose the action of the extensors.

b. The elbow extensors are the agonists and shoulder girdle muscles act as fixators is a true statement. To isolate the movement to the elbow, the shoulder muscles stabilize the shoulder so it doesn't move.

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