What occurs during isotonic contractions?

During isotonic contractions, the muscles indeed shorten and lengthen while maintaining a constant load. This type of contraction is characterized by the ability of the muscle to change its length while producing movement. Specifically, isotonic contractions can be divided into two phases: concentric and eccentric. In the concentric phase, the muscle shortens as it contracts to lift a load, while in the eccentric phase, the muscle lengthens while still under tension to control a movement as the load is lowered.

This contrasts with other types of muscle contractions. For instance, if muscles develop tension without changing length, that describes an isometric contraction. Similarly, a static position refers to isometric contractions where the muscles are engaged but do not cause any movement. Lastly, if the muscles contract without movement, this again indicates an isometric contraction, not isotonic. Thus, the nature of isotonic contractions is precisely about movement and changes in muscle length while acting against a consistent load.