Final answer:
An isometric contraction is when the muscle develops tension without changing its length, leading to no movement, which is why the direct answer to the question is D. Isometric.
Step-by-step explanation:
During an isometric contraction, the muscle develops tension but does not change length. No movement occurs as the force generated by the muscle is not sufficient to move the load. This contrasts with an isotonic contraction, where muscle tension remains constant while the muscle changes length to move a load. Isometric contractions are common in daily activities, such as maintaining posture or holding objects still.
For instance, when you try to lift something that is too heavy for you, your muscles are engaged in an isometric contraction since they generate force but the object does not move.