Dr. Dwayne Jackson

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Vital Science Stress Rest and Growth



Rest Days: We All Need Them


Dwayne N. Jackson, PhD


You’ve likely heard the saying, “that which does not kill you, only makes you stronger”. But, when we apply this anecdote to stress and adaptation, it’s only partially true.

Although the body has a remarkable ability to adapt to stress, it can only do so if there is sufficient recovery and availability to necessary resources between stressful events.



Stress is something experienced by all of us, no matter who we are, and it has both positive and negative effects on our lives. In our world we have an abundance of opportunities to experience negative stress (distress) and positive stress (eustress) on a daily basis.


It doesn’t matter where it comes from, the day-to-day stress we experience accumulates…


Work stress, diet stress, pandemic stress, financial stress, commuting stress, parental and family stress, and relationship stress are all examples of common stressors that contribute to our daily allostatic (stress) load.


The accumulation of stress significantly impacts our body’s neurotransmitters and hormones. Physical and behavioral changes occur as a response to these stressors. Once a threshold is reached, our “stress system” releases neurotransmitters/hormones in the brain and in peripheral tissues through activation of the autonomic sympathetic nervous system and the hypothalamic–pituitary–adrenal axis.


When stress becomes unmanageable,  hormonal regulation fails and we experience unhealthy dysregulation of hormones and neurotransmitters.


Exercise, being a positive stress, is an excellent way to buffer the negative effects of “bad stress”. But there’s a hitch—when heavy training cycles are combined with everyday stressors like dieting and workplace stress are compounded by other negative stressors, you risk pushing yourself into a state of overtraining.



What is Overtraining Syndrome?


Overtraining syndrome is a maladaptive response to excessive exercise when it’s not being satisfied with appropriate nutrition and rest. The imbalance between heavy training and recovery is worsened by inadequate nutrition, illness, psychosocial stressors and sleep disorders. When left unchecked, overtraining leads to dysfunction of pathways and responses in immune, inflammatory, neurological, hormonal and metabolic systems.


If you are training heavily, lead a stressful life, and are recently experiencing many of the following symptoms, then you may be pushing into an overtraining state:


  • Unexplained fatigue
  • Bloating
  • Gut health issues
  • Difficulty losing weight
  • Unexplained weight gain/loss
  • Moodiness and irritability
  • Increased heart rate at rest
  • Trouble falling or staying asleep
  • Headaches
  • Numbness or tingling in hands or feet
  • Foggy head
  • Unexplained injuries
  • Slow recovery from workouts
  • Body aches and pains
  • Anxiety and panic attacks
  • Changes in menstruation (e.g., period off schedule or missed, heavier or lighter periods)



Stress without rest = hormonal imbalances


There are several important hormones affected by stress and overtraining. If you noted any of the symptoms above, here are the key neurotransmitters/hormones that are likely hindering your progress:




Catecholamines, such as dopamine, norepinephrine (noradrenaline), and epinephrine (adrenaline) are released from neurons in the brain, sympathetic nerves, and the adrenal medulla. As hormones, they circulate in the blood and prepare the brain and body for stress. If stress prevails and the nervous system is activated chronically (as seen during chronic mental stress and in overtrained strength athletes), then the catecholamines produce negative mental health effects (poor sleep quality, anxiety, etc.) and cardiovascular consequences (elevated heart rate, hypertension, atherosclerosis, etc.). In overtrained endurance athletes, catecholamine levels may decrease over time, leading to cardiovascular dysregulation, slow heart rate, low blood pressure, slow recovery, low energy, poor focus, low motivation, mood disorders, and weight gain.


Cortisol (with special guests, leptin and ghrelin)


Mental stress leads to chronic activation of the hypothalamic-pituitary-adrenal axis and cortisol dysregulation. Under such conditions, cortisol is elevated throughout the day/night. Chronically elevated cortisol promotes increased appetite and food intake by decreasing (hunger inhibiting) leptin signalling and increasing (appetite stimulating) ghrelin signalling. This hormonal state stimulates significant fat accumulation, generally around the waist. Studies have shown that chronically elevated blood cortisol promotes amenorrhea (lack of menstruation) in athletes. If you notice changes in your menstrual cycle during heavy training cycles, you may be experiencing cortisol dysregulation.


Thyroid Hormones (TSH, T3, T4)


Thyroid function is down-regulated under prolonged stressful conditions. Cortisol, suppresses pituitary function, blunts thyroid-stimulating hormone (TSH) release, and thereby limits thyroid hormone (T3/T4) production, promoting hypothyroidism. Some symptoms of hypothyroidism include, fatigue, increased sensitivity to cold, weight gain, dry skin, puffy face, weakness, muscle aches, pain and swelling in joints, thinning hair, depression, and memory issues.



4 daily life strategies to quickly improve your resilience to stress:


  1. Sleep well (8-9 hours per night)

No screen time before bed, decrease the temperature of your bedroom, avoid alcohol and stimulants altogether, read and/or meditate before bed.


  1. Eat well and stay hydrated

Supply your body with adequate nutrition and calories. Anyone who has prepared for a bodybuilding, physique, or bikini competition knows what dieting stress feels like. In the offseason, maintain a diet high in lean protein (1.8 to 2.2 g/kg body weight), ingest an abundance of healthy fats including omega-3 (flax, fish, supplements), maintain high intake of phytonutrient dense foods (like berries and vegetables). Limit refined sugars and fast foods that promote inflammation. Protect your gut health, eat foods that are “gut friendly”. Drink 3-4 L per day and don’t forget to use electrolytes when you sweat.


  1. Be Mindful

Daily mindful meditation, mindful breathing, and other mindful exercises (e.g., visualization, toga, tai chi), that increase our sense of presence, have been clinically shown to improve our ability to handle stress.


  1. Train Smart

Exercise is one of the best ways to protect hormonal balance and build stress resilience. However, during stressful times, it’s much easier to push your body too hard and into the “overtraining danger zone”. This is because many of the hormonal changes we experience under chronic stress limit the body’s ability to recover from physical stress.



6 simple training tips to prevent overtraining:


  • Periodize your training
  • Adjust training volume and intensity based on performance and mood
  • Ensure adequate calories are consumed around the workout window
  • Hydrate with electrolytes throughout the day and through the workout window
  • Rest 24-48 hours between training sessions for the same muscle groups
  • Abstain from training if you are sick, have an infection, or are under extreme stress
  • If your body is telling you to take a day off, do it!




Dr. Dwayne N. Jackson, is an active Medical School Professor and Medical Scientist in the Department of Medical Biophysics at Western University in Canada. He is a world leader in the areas of medical physiology, exercise physiology, health, nutrition, and supplementation. Dr. Jackson’s innovations in research and education have led to numerous scientific awards, teaching awards, peer-reviewed scientific articles, and important advances in medicine and human health.


If you want to know more about optimizing your health through real science, check out www.yourvitalscience.com and follow Dr. Jackson on Instagram: @drdnjackson




Jennifer L. Copeland, Leslie A. Consitt, Mark S. Tremblay, Hormonal Responses to Endurance and Resistance Exercise in Females Aged 19–69 Years, The Journals of Gerontology: Series A, Volume 57, Issue 4, 1 April 2002, Pages B158–B165.

Cadegiani FA, Kater CE. Hormonal aspects of overtraining syndrome: a systematic review. BMC Sports Sci Med Rehabil. 2017 Aug 2;9:14. doi: 10.1186/s13102-017-0079-8. PMID: 28785411; PMCID: PMC5541747.

Meeusen R, Duclos M, Foster C, Fry A, Gleeson M, Nieman D, Raglin J, Rietjens G, Steinacker J, Urhausen A, European College of Sport Science. American College of Sports Medicine Prevention, diagnosis, and treatment of the overtraining syndrome: joint consensus statement of the European College of Sport Science and the American College of Sports Medicine. Med Sci Sports Exerc. 2013;45(1):186–205.

Galante J, Dufour G, Vainre M, Wagner AP, Stochl J, Benton A, Lathia N, Howarth E, Jones PB. A mindfulness-based intervention to increase resilience to stress in university students (the Mindful Student Study): a pragmatic randomised controlled trial. Lancet Public Health. 2018 Feb;3(2):e72-e81.

Meeusen R, Duclos M, Gleeson M, et al. The overtraining syndrome: facts and fiction. Eur J Sport Sci. 2006;6(4):263

Meeusen R, Duclos M, Gleeson M, et al. Prevention, diagnosis and treatment of the overtraining syndrome: ECSS Position Statement Task Force. Eur J Sport Sci. 2006;6(1):1-14



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