Final answer:
Isotonic muscle contractions, which involve change in muscle length, are often preceded by isometric contractions (option 1), where tension is generated without changing muscle length.
Step-by-step explanation:
Isotonic muscle contractions are characterized by a change in muscle length while the tension stays constant, often involved in movements where a load is moved. One common type of isotonic contraction is the concentric contraction, in which muscles shorten to move a load, like when you lift a weight with your biceps brachii. However, before isotonic contractions, there usually is an isometric contraction, during which the muscle generates tension without changing length.
An example of an isometric contraction is when you try to lift something that is too heavy for you. The muscles generate force, but the load does not move, so the muscle does not change length. Isometric contractions can be considered a precursor or starting phase for isotonic contractions, where, upon overcoming the load's resistance, the muscle transitions into either concentric or eccentric isotonic contractions to move the load. Therefore, to answer the question, isotonic muscle contractions are often preceded by isometric contractions. Once the initial tension required to hold the load in place has been built up during the isometric contraction, and assuming the muscle can generate sufficient force to move the load, it then transitions into isotonic contraction (either concentric or eccentric) to complete the movement.