Final answer:
Isometric contractions do not move a load, while concentric contractions involve muscle shortening to move a load, and eccentric contractions occur as muscle tension diminishes and the muscle lengthens.
Step-by-step explanation:
An isometric contraction occurs when the muscle produces tension without changing the angle of a skeletal joint. Isometric contractions do not move a load, as the force produced cannot overcome the resistance provided by the load. An example of an isometric contraction is holding your head in an upright position to maintain posture.
A concentric contraction involves the muscle shortening to move a load. An example of this is the biceps brachii muscle contracting when a hand weight is brought upward. As the biceps brachii contract, the angle of the elbow joint decreases as the forearm is brought toward the body.
An eccentric contraction occurs as the muscle tension diminishes and the muscle lengthens. An example of this is when the biceps brachii muscle lowers a hand weight in a slow and controlled manner. As tension is released from the biceps brachii, the angle of the elbow joint increases.