What describes isotonic contractions?

Isotonic contractions are characterized by the muscle shortening or lengthening while producing movement, typically against a constant resistance. This type of contraction allows for motion through a range of motion, which is essential for activities such as lifting weights. During an isotonic contraction, the force generated by the muscle exceeds the resistance, allowing for dynamic movement, which effectively helps in strengthening and toning muscles.

In contrast, other types of contractions may involve no movement, varying resistance, or no resistance at all, which do not align with the definition of isotonic contractions. Therefore, the accurate description of isotonic contractions highlights their capability to facilitate movement against a steady resistance, making option B the correct choice.