Final answer:
True, the length of a muscle fiber at the onset of contraction affects force generation due to the length-tension relationship, where optimal overlap of myosin and actin allows for maximum cross-bridge formation.
Step-by-step explanation:
True, fiber length at the onset of contraction can have an effect on the force generated. In skeletal muscle contraction, the length-tension relationship is fundamental in determining the strength of a muscle contraction. A skeletal muscle fiber generates force by the cross-bridge cycling between myosin heads and actin within the sarcomeres. The position of the thick and thin filaments relative to one another when contraction begins influences the number of cross-bridges that can form, hence directly affecting the force produced. The optimal length allows for the maximum number of myosin-actin interactions, resulting in a more potent contraction.