The cricothyroid muscles are paired muscles located inside the larynx that are critical in controlling pitch. Specifically, the cricothyroid muscles lengthen the vocal folds by pulling the thyroid cartilage forward. In contrast, the thyroarytenoid muscles shorten the vocal folds. Research has shown that trained vocalists tend to balance the actions of cricothyroid and thyroarytenoid muscles, utilizing neither to their maximum potential. Scientists theorize that humans naturally are inclined to use all or none of a particular muscle. Training can help vocalists use just part of a particular laryngeal muscle's capability and so produce a more balanced, accurate, and controlled tone.