Final answer:
Muscle force can be higher during eccentric contractions when muscles lengthen under tension compared to concentric contractions where muscles shorten and isometric contractions where muscle length does not change. The nervous system, specifically motor units, regulate the contractions and muscle tone.
Step-by-step explanation:
The muscle forces generated during eccentric, isometric, and concentric contractions vary. During concentric contractions, the muscle shortens as it generates force, primarily to move a load. An example is the biceps brachii shortening when you lift a hand weight. In eccentric contractions, the muscles lengthen while still generating force, often to control the lowering of a load, like when slowly lowering a hand weight. Isometric contractions involve no change in muscle length but a build-up of muscle tension, such as when holding a weight steady without moving it.
All of these muscle activities are finely controlled by the nervous system, which regulates the muscle contractions, fiber recruitment, and muscle tone. A motor unit plays an integral role in the nervous system control of skeletal muscles. In general, higher forces can be generated during eccentric contractions compared to concentric and isometric contractions, although this can depend on various factors such as velocity of the contraction and the load involved.