Final answer:
An isometric contraction is when the muscle increases tension without shortening, as opposed to isotonic contractions where muscle length changes. Isometric contractions are essential for maintaining posture and stability without producing movement.
Step-by-step explanation:
An isometric contraction is one in which the length of the muscle does not change significantly. This occurs when the muscle produces tension but the force is not enough to move a load, which results in a steady muscle length. During isometric contractions, sarcomere shortening happens and there is an increase in muscle tension, yet the angle of the joint does not change. This is contrasted with isotonic contractions, where muscle length changes, and a load is moved as the muscle shortens or lengthens. Isotonic contractions are further divided into concentric, where the muscle shortens as it contracts, and eccentric, where the muscle lengthens while maintaining tension.
Isometric contractions play a vital role in everyday activities such as maintaining posture and stabilizing bones and joints without moving them. For instance, holding a heavy weight without moving it would involve an isometric contraction because the muscle tension increases, but the muscle does not shorten to cause movement.