The endocrine system helps maintain homeostasis by responding to external stimuli, including the stress of exercise. It works as a communication network that coordinates physiological changes needed for performance, recovery, and long-term adaptation to training. These endocrine responses matter both during a single workout (acute responses) and across weeks or months of training (chronic adaptations).
Hans Selye first described adaptation to stress using the term General Adaptation Syndrome (GAS). GAS explains how the body responds to a stressor over time. The model includes three stages:
In strength training, repeated exposure to appropriately managed stress leads to training adaptation. With enough recovery, the body not only returns to baseline but can improve performance. This idea supports periodization: you alternate planned training stress with planned recovery to drive systematic adaptation.
Hormonal signaling regulates many exercise responses by influencing both anabolic (building) and catabolic (breaking down) processes. The endocrine response to resistance training depends on several program variables, including:
Both acute and chronic changes in circulating hormone levels are shaped by how the program is structured. For that reason, program design should align with the specific adaptations you want to emphasize.
Hormones are chemical messengers made, stored, and released by endocrine glands. After release, they travel through the bloodstream to target tissues, where they trigger specific physiological responses. Endocrine glands commonly involved in exercise responses include:
Endocrine glands secrete various hormones that support exercise performance and training adaptation. Key hormones and their actions include:
Exercise training triggers both endocrine and paracrine responses. Hormonal responses to resistance exercise are influenced by factors such as the amount of muscle mass involved, exercise intensity, and training volume. Key signaling mechanisms include:
Hormones affect only tissues that have the appropriate receptors. Receptors are typically located:
The lock-and-key theory describes how a hormone binds to a specific receptor to produce an effect. In practice, hormone-receptor interactions can be more complex. For example, cross-reactivity and allosteric binding can change how strongly a hormone signal is expressed.
Muscle tissue is a major target for anabolic and catabolic hormones. These hormones contribute to training adaptations through mechanisms such as:
Hormonal effects depend on receptors, which can be located in different parts of the cell. Several factors influence the strength and outcome of hormonal signaling:
Some hormones circulate with binding proteins that help transport them in the bloodstream and extend their activity. One example is sex hormone-binding globulin (SHBG), which binds testosterone and estrogen. In addition, catecholamines (epinephrine and norepinephrine) act as key acute hormones, supporting force production and increasing energy availability during exercise.
Hormones produce effects by binding to specific receptors in target tissues. The lock-and-key theory explains this basic idea: hormones (keys) bind to receptors (locks) to trigger cellular responses. This interaction can be modified by several factors, including:
Exercise-induced stress can also affect receptor function. In some cases, training increases receptor sensitivity and number, which can support improved muscle adaptation.
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