Final answer:
Muscle contraction is influenced by the initial stretch of the muscle, degree of stretching, contraction extent, and neuromuscular junction activity.
Step-by-step explanation:
The factors that affect muscle contraction in terms of stretching include how stretched the muscle was before stimulation, an over-stretched muscle, an over-contracted muscle, and the site where a nerve fiber communicates with a muscle fiber, known as the neuromuscular junction (NMJ).
An optimal muscle contraction occurs when there is a maximal overlap between actin and myosin filaments within the muscle's sarcomeres, leading to the greatest number of cross-bridges being formed. When a muscle is excessively stretched or overly contracted, the zone of overlap decreases, resulting in less effective cross-bridge formation and thus weaker muscular contractions. At the NMJ, the neurotransmitter acetylcholine (ACh) triggers the depolarization of the muscle fiber, leading to the release of calcium from the sarcoplasmic reticulum and enabling the actin-myosin cross-bridging that results in a muscle contraction.