Final answer:
A concentric contraction is a type of muscle contraction where muscles shorten to generate force, as seen when the biceps lift a weight upward.
Step-by-step explanation:
The type of contraction that generates force by causing the muscles to shorten is known as a concentric contraction. In a concentric contraction, the muscle fibers shorten actively, and this shortening creates the force needed to move a load. This type of contraction is a subtype of isotonic contractions, where muscle length changes, but muscle tension remains constant. The classic example of concentric contraction is when the biceps muscle contracts to lift a hand weight upward, causing the forearm to move toward the body and decreasing the angle of the elbow joint. As the biceps shorten, sarcomeres shorten, cross-bridges form, and the myosin heads pull the actin, moving the load.