by Essentials of Strength and Conditioning 4th Edition With Web Resource
Kinetic Select June 2017
The following is an exclusive excerpt from the book Essentials of Strength Training and Conditioning-4th Edition With Web Resource, published by Human Kinetics. All text and images provided by Human Kinetics.
The catecholamines—primarily epinephrine but also norepinephrine and dopamine—are secreted by the adrenal medulla and are important for the acute expression of strength and power because the hormones act as central motor stimulators and peripheral vascular dilators and enhance enzyme systems and calcium release in muscle (95). Thus, the resistance exercise–induced stress leads to events similar to the classic fight-or-flight response. The importance of catecholamines during resistance exercise was highlighted by the finding that men who had a higher catecholamine release immediately before and during a heavy resistance exercise session were able to better maintain force output throughout the session (53). The role of catecholamines in growth-promoting actions in muscle tissue is less clear, but they act to stimulate other anabolic hormones.
The physiological functions of epinephrine and norepinephrine in muscle are these:
Increase force production via central mechanisms and increased metabolic enzyme activity
Increase muscle contraction rate
Increase blood pressure
Increase energy availability
Increase muscle blood flow (via vasodilation)
Augment secretion rates of other hormones, such as testosterone
Catecholamines appear to reflect the acute demands and physical stress of resistance exercise protocols (105). A high-intensity (10RM), short-rest (10-60 seconds between sets and exercises), heavy resistance exercise routine (10 exercises, three sets) typically used by bodybuilders for development of strength and hypertrophy was shown to maintain increased plasma norepinephrine, epinephrine, and dopamine levels for 5 minutes into recovery (105). In addition, epinephrine has been correlated to lactate concentrations with exercise stress. Adrenal responses are not involved in the recovery responses until the stress is removed. Some specific endogenous opioid peptides (i.e., proenkephalins) are secreted by the adrenal medulla and affect the immune system, which is critical in recovery from exercise stress (182). If training is not varied, continued stress keeps the adrenal gland engaged, and recovery is delayed due to the secondary responses of cortisol and its negative effects on immune system cells and protein structures. Long-term continued high stress can even lead to adrenal exhaustion, at which point the ability of the adrenal medulla to release catecholamines is diminished.
Heavy resistance training has been shown to increase the ability of an athlete to secrete greater amounts of epinephrine during maximal exercise (104). It has also been suggested that training reduces epinephrine responses to a single bench press workout (68). Because epinephrine is involved in metabolic control, force production, and the response mechanisms of other hormones (such as testosterone, GHs, and IGFs), stimulation of catecholamines is probably one of the first endocrine mechanisms to occur in response to resistance exercise.
Developed by the National Strength and Conditioning Association, Essentials of Strength Training and Conditioning, Fourth Edition, is the fundamental preparation text for the Certified Strength and Conditioning Specialist® (CSCS®) exam as well as a definitive reference that strength and conditioning professionals will consult in everyday practice. The book is available in bookstores everywhere, as well as online at the NSCA Store.