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Neuroendocrine Adaptation - Your "End-Run" Around the Menopause Transition
Constantly Varied Functional Movement at High Intensity... Sound Familiar?
Photo Credit: Three Metabolic Energy Systems. Glassman G: Forging Elite Fitness; CrossFit Journal June 2003
My Friends... When our hormones decline and our body changes, understanding our physiology can help us reconfigure our fitness and nutrition strategies to maximize our health and vitality. Some might call it a hack - I call it hormone mastery! Enjoy! -Carla
Exercise is a physical stress that challenges homeostasis (physiologic “balance” or “equilibrium”). In response to this physical challenge, the body responds to re-establish this physiologic balance. This response is called neuroendocrine adaptation.
The response of the body to a stressor is complex and involves the cerebral cortex (brain), brain stem (“instinctual” center), activation of the sympathetic nervous system (“fight or flight” response), two integrated endocrine systems involving the hypothalamus in the brain (H), pituitary gland (P) and adrenal (A) glands (HPA axis) as well as the reproductive (G) system (HPG axis) and the immune system (proinflammatory cytokines). Synchronized activation of these pathways occurs in response to chronic (ongoing) stressors or transiently in response to a specific task, such as exercise or sport. The goal of this response is to return the body to a stable equilibrium, or adaptation.
Here is a quick primer on the main hormonal players in the neuroendocrine response system:
HPA Axis: Brain/brain stem (asses the task): Corticotropin Releasing Hormone (CRH) —> Pituitary gland (Adrenocorticotropic Hormone (ACTH) (also growth hormone, prolactin, and vasopressin) —> Adrenal glands (Cortisol, Testosterone).
HPG Axis: Brain/brain stem (endorphins, (GNRH)) —> Pituitary gland (Follicle stimulating hormone (FSH) and Luteinizing Hormone (LH)) —> ovaries (Estrogen, Testosterone).
Sympathetic Nervous System: Brain/Brain stem (endorphins, CRH) ->Pituitary Gland (ACTH) —> Adrenal Glands (Norepinephrine, Epinephrine, Cortisol, other glucocorticoids).
Immune System: Tumor necrosis factor-alpha (TNF-alpha), Interleukin-1 (IL-1), and Interleukin 6 (IL-6): Initially augments the above pathways, then inhibits them once the response nears completion to “reset” the system. These pro-inflammatory cytokines also aid in tissue repair.
Once the neuroendocrine response system is activated, this cascade of responses is elicited so that the body can execute the task/answer the stressor effectively.
In the case of exercise, the neuroendocrine adaptation that results from effective response to training achieves a new, fitter, stronger, faster equilibrium. The ability of the body to adapt to a training stimulus is a key component of gaining physical fitness!
During the menopausal transition, ovarian production of estrogen and testosterone declines. As a result, we see a reduction in muscle mass, power, and function. However, when the neuroendocrine response pathways are activated by exercise, it elicits a response to the training stressor which, when effective, results in adaptation which is your fitter, stronger, faster equilibrium.
Neuroendocrine stimulation and adaptation become more critical during mid-life when our baseline hormone levels that promote muscle mass, function, and bone density are in decline. The neuroendocrine response pathway provides a way to compensate for the declining estrogen stimulus that comes with the menopausal transition.
To understand the basis of neuroendocrine adaptation, let’s take a closer look at the metabolic systems that provide energy for all types of physical activity.
Three Metabolic Energy Systems
There are 3 metabolic pathways that provide energy for every type of human activity:
Phosphocreatine Pathway: Utilizes creatine phosphate to fuel movements lasting < 10 seconds (ex - a 1 rep maximum deadlift). Does not require oxygen (anaerobic).
Glycolytic Pathway: Utilizes glucose stored in the muscles (predominantly anaerobic) to fuel moderately powered movements lasting up to several minutes (ex- a 1-2 min high intensity running interval).
Oxidative Pathway: Utilizes carbohydrate, fatty acids, and protein to fuel low-powered, longer-duration activities in excess of several minutes. Requires oxygen (aerobic). (ex - long endurance run).
Building competency with movements in all three pathways sets the stage for developing the adaptive ability to move among these pathways in short periods of time.
How to Stimulate Neuroendocrine Adaptation
Train with functional movements: These are complex movements that require the recruitment of multiple muscle groups by the nervous system and coordination using the brain, sense of balance, and body control. An example would be a barbell squat as compared to a leg press machine. Other functional movements include push-ups, pull-ups, jumping, rope skipping, box/bench triceps dips, and running, to name a few.
Mix it up!: Moving between different metabolic energy systems in a short period of time requires a high level of neuroendocrine stimulation and adaptation. An example would be a workout that prescribes 5 heavy deadlifts (Glycolytic pathway) and an 800m row or run (Phosphorylative pathway) performed in sequence 5 times.
Interval Training: High-intensity training with intervals of work alternating with intervals of rest. An example would be sprint interval training (SIT) with 30 seconds of maximum effort alternating with 30 seconds of rest or a classic Tabata with 20 seconds of maximum effort and 10 seconds of rest.
Low repetition, heavy barbell lifts: Performing heavy barbell lifts for 5 sets of a 1-3 repetition maximum (with solid technique!) with 3 minutes of rest between sets stimulates the phosphocreatine pathway.
Try something new!: If you are a CrossFitter you have undoubtedly experienced looking at the Whiteboard outlining the daily workout and getting a little bit nervous because there are movements you may not have done before. This is a good thing! That nervous feeling is your sympathetic nervous system ramping up before you even start the workout!
Constant Variation in Movement: The Human body has an amazing ability to adapt to repetitive movement. Once the body has adapted to a certain movement pattern, performing those same movements does not elicit the same level of neuroendocrine stimulation as compared to the first time they were performed. When movements vary, it “keeps the neuroendocrine system guessing” and adapting to each new stimulus.
A Word About Chronic Stress and Over-Training
The neuroendocrine response described thus far is transient for the time required to complete the physical task. Once the task is completed, the hormones and cytokines return to baseline in about 30 minutes. Following this period, a new fitter, faster, stronger equilibrium is achieved as the tissues recover, repair, and rebuild.
In some cases, such as over-training, chronic energy deficits, sleep deprivation, and life stress, the neuroendocrine responders do not return to baseline. Instead, there is chronic activation of the neuroendocrine pathways and pro-inflammatory cytokines that results in insufficient tissue repair and rebuilding that cannot “catch up” with the ongoing stress. When the next stimulus is encountered, the ability to adapt is impaired and the fitter, faster, stronger equilibrium is not achieved. As a result, muscle health suffers, injuries develop, and performance declines.
Mid-Life women are particularly sensitive to the effects of chronic cortisol stimulation underscoring the importance of managing chronic stressors so that the system can return to baseline and allow sufficient tissue recovery and repair so that you become fitter, faster, and stronger with every training session. Here are some tips for dialing down the stress response:
Sleep - The foundation of recovery.
Proper fueling - Stay out of that energy deficit!
Avoid over-training - Work with a coach. Design a program with shorter duration/higher intensity and more productive training sessions that incorporate a variety of movements that build fitness in all 3 metabolic energy pathways.
Massage, bodywork, mobility movements, tissue care - make friends with the foam roller and the cold shower.
Yoga, meditation, mindfulness - Where your mind goes, your body will follow.
Consider Adaptogens: Adaptogens are derived from plants and help manage the stress response. For a great description of various adaptogens and their effects, check out Next Level by Dr. Stacy Sims and Selene Yeager.
By incorporating variability in movement and intensity and effectively managing the stress response following training, you will keep your neuroendocrine response system sharp and ready to adapt so you can achieve your fittest, fastest, strongest self!