Resistance Training Adaptations: Endocrine Changes
  • Resistance Training Adaptations: Endocrine Changes
    Many hormones have effects on either the growth or the degradation of tissue, such as muscle tissue. Understanding these hormones is important for designing effective training programs.
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    The following is an exclusive excerpt from the book NSCA's Essentials of Personal Training, Second Edition, published by Human Kinetics. All text and images provided by Human Kinetics.

    Hormones are blood-borne molecules that are produced in glands called endocrine glands. There are two primary types of hormones: (1) protein and peptide hormones and (2) steroid hormones. Two examples of protein and peptide hormones are growth hormone and insulin. Steroid hormones are all derived from a common precursor (cholesterol) and include hormones such as testosterone (the primary male sex hormone) and estrogen (the primary female sex hormone).

    Many hormones have effects on either the growth or the degradation of tissue such as muscle tissue. Anabolic hormones such as testosterone, growth hormone (GH), and insulin tend to stimulate growth processes in tissues, while catabolic hormones such as cortisol use tissue degradation to help maintain homeostasis of variables like blood glucose. The concentration of many of these hormones is affected by an acute bout of exercise. Indeed, changes in some hormone concentrations are needed to support the metabolic response to exercise. For example, exercise results in increases in concentrations of epinephrine. Epinephrine increases fat and carbohydrate breakdown by the cell so that more ATP will be available for muscle contraction. Epinephrine also has effects on the central nervous system, which may facilitate motor unit activation.

    Other hormone concentrations are increased during a bout of resistance training. Acute increases in anabolic hormones may have little effect on a particular exercise bout, but they likely play an important role in stimulating adaptations to training. For example, testosterone and GH concentrations are elevated with resistance training in males (50, 71, 75, 76, 111). These hormones stimulate increases in skeletal muscle protein synthesis. Therefore, they are important for development of muscle mass. The cumulative effect of acute increases in testosterone and GH concentrations with repeated training sessions may contribute to the long-term accretion of muscle mass. Indeed, the repeated increases in anabolic hormone concentrations during multiple training bouts over time may be a more potent endocrine stimulus than any changes in chronic hormone concentrations (75).

    The hormonal response to resistance exercise is dependent on the characteristics of the training bout. As a general rule, bouts that have higher volume and shorter rest periods elicit stronger endocrine responses than do bouts with lower volume and longer rest periods (14, 69, 75), although the differences between protocols may diminish with prolonged training (14). Similarly, large muscle mass exercises have a more powerful stimulus than do small muscle mass exercises (75). Other factors such as sex and age can affect the acute endocrine response. Males tend to have larger acute changes in anabolic hormone concentrations than do females (25). Similarly, elderly individuals tend to exhibit an attenuated anabolic hormonal response to training relative to younger individuals (25).

    NSCA’s Essentials of Personal Training, Second Edition, is the authoritative text for personal trainers, health and fitness instructors, and other fitness professionals, as well as the primary preparation source for those taking the National Strength and Conditioning Association Certified Personal Trainer® (NSCA-CPT®) exam. The book is available in bookstores everywhere, as well as online at the NSCA Store.

  • Disclaimer: The National Strength and Conditioning Association (NSCA) encourages the exchange of diverse opinions. The ideas, comments, and materials presented herein do not necessarily reflect the NSCA’s official position on an issue. The NSCA assumes no responsibility for any statements made by authors, whether as fact, opinion, or otherwise. 
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