Part 2/14:
French describes a fascinating link: engaging motor units under substantial loads isn't just about building muscle—it also signals the endocrine system, prompting hormone release like testosterone. While traditionally thought of as a testosterone hormone primarily from testes in men and adrenal glands in women, French clarifies that resistance exercise triggers this hormonal cascade via mechanical and metabolic stress responses, which activate sympathetic arousal and the hypothalamic-pituitary-adrenal (HPA) axis. This cascade results in the release of catecholamines, such as epinephrine and norepinephrine, which influence adrenal hormone secretion, ultimately leading to testosterone release from the adrenal glands, especially in women.