Why this bookTraining may seem like a simple act-only on the surface.Behind every movement, a complex network of biological responses is activated, involving hormones, the nervous system, metabolism, and perception.This book was born from the desire to understand what truly happens in the body when we train, and why the response to the same stimulus can vary so deeply from person to person and from moment to moment.Exercise is not a mechanical act.It is a stimulus that the organism interprets.Throughout my academic path and practical work in the field, it became increasingly clear that performance, recovery, and adaptation do not depend exclusively on training load, but on the overall biological context in which that stimulus is placed.Hormones, stress, recovery quality, and emotional state profoundly influence how the body responds.In this framework, music represents an often underestimated element. Not as mere motivational background, but as a stimulus capable of modulating the physiological response, influencing activation, perceived effort, and recovery.The goal of this book is not to offer quick solutions or rigid protocols, but to provide a perspective for understanding the body as an integrated and adaptive system.Training, music, and thought are not treated as separate domains, but as parts of a single biological dialogue.This work originates from an academic thesis, but it has been rewritten to be accessible even to those without a specific scientific background, while maintaining conceptual solidity and respect for the original content.