Final answer:
Isotonic contractions involve a change in muscle length while maintaining constant tension and include concentric and eccentric movements, as seen in weight lifting. Isometric contractions occur without changing muscle length and increase tension but do not move a load, important for posture and stability.
Step-by-step explanation:
The key difference between isotonic and isometric muscle contractions lies in muscle movement and tension. An isotonic contraction is characterized by a change in muscle length to move a load while muscle tension remains constant. There are two forms of isotonic contractions: concentric, where the muscle shortens, and eccentric, where the muscle lengthens under tension. For example, when lifting a weight with the biceps brachii, the upward movement is a concentric contraction, while lowering the weight is an eccentric contraction.
In contrast, during an isometric contraction, muscle length stays the same, as the muscle cannot move the load due to the load exceeding the muscle's tension capacity. This type of contraction increases muscle tension without causing movement. Isometric contractions are common in maintaining posture and stability, such as holding the head upright.
Understanding these contractions helps in identifying how muscles work during various activities and in designing appropriate training regimens for different athletic and rehabilitation purposes.