Muscle contractions can be classified into three main types: isometric, concentric, and eccentric. In an isometric contraction, the muscle generates force without changing its length, such as when holding a weight steady. In a concentric contraction, the muscle shortens while generating force, like when lifting a weight. On the other hand, an eccentric contraction occurs when the muscle lengthens while still producing force, such as when lowering a weight. Each type of contraction plays a crucial role in various physical activities and exercises, contributing to strength, stability, and overall muscle function.