Final answer:
The strongest muscle contractions are achieved by concentric contractions.
Step-by-step explanation:
The strongest muscle contractions are normally achieved by D) Concentric contractions.
In isotonic contractions, where the tension in the muscle stays constant, a load is moved as the length of the muscle changes (shortens). Concentric contractions involve the muscle shortening to move a load. An example of this is the biceps brachii muscle contracting when a hand weight is brought upward with increasing muscle tension. As the biceps brachii contract, the angle of the elbow joint decreases as the forearm is brought toward the body.
Eccentric contractions occur as the muscle tension diminishes and the muscle lengthens. Isometric contractions occur as the muscle produces tension without changing the angle of a skeletal joint, but they do not move a load.