Final answer:
When an agonist muscle group is concentrically activated, the antagonist muscle group relaxes to allow the movement. The agonist shortens, as in a bicep curl, while the antagonist, like the triceps, lengthens.
Step-by-step explanation:
When the agonist muscle group is activated in a concentric manner, the antagonist muscle group must relax and lengthen to allow the movement to occur. During a concentric contraction, the agonist muscle shortens to move a load, like the biceps brachii muscle contracting to lift a weight. As this happens, the antagonist muscle group, in this case, the triceps brachii, elongates and yields to the movement. Antagonists play a significant role in muscle function by maintaining body or limb position and controlling rapid movement. For proper joint function and movement coordination, the simultaneous contraction of the agonists and relaxation of the antagonists is crucial.
When the agonist muscle group is activated in a concentric manner, the antagonist muscle group opposes or resists the movement. For example, when the quadriceps femoris muscle group contracts concentrically to extend the knee, the hamstrings muscle group acts as the antagonist and flexes the knee joint.