Addiction to Exercise – what distinguishes a healthy level of commitment from exercise addiction? BJSM
British Journal of Sports and Exercise Medicine, Dr N Keay, Sport and Dance Endocrinologist writes: Addiction to Exercise – what distinguishes a healthy level of commitment from exercise addiction? Read More
Endocrine system: balance and interplay in response to exercise training
By Dr Nicky Keay, Sports/Dance Endocrinologist
The process of homeostasis maintains a steady internal milieu. So how is it possible for adaptations to occur? What are the internal mechanisms that determine a good outcome versus a negative one?
Changes in the external environment, such as exercise training, challenge homeostasis, producing spatial and temporal responses in the internal environment. These cause interactions between muscle, bone and gut, modulated by the Endocrine system. The degree and nature of these responses dictate whether a positive adaptation occurs. An excessive response, or a response not in tune with the networks of the Endocrine system, can hinder adaptation or produce a maladaptive response. The balance and interplay of internal responses are crucial in determining the outcome to exercise training in the individual.
Local responses in exercising tissues
Exercising tissues release exerkines (metabolites, nucleic acids, peptides) which are packaged in exosomes and microvesicles. The content of these vesicle packages increases with intensity of endurance exercise in a dose-dependent manner. These exerkines have autocrine and paracrine effects, which modulate systemic adaptations to endurance exercise in the tissues themselves and those in the vicinity.
The range of these molecular responses from exercising tissues has been identified applying multi-omics (epigenomic, transcriptomic and proteomic analyses). Furthermore variance in trainability has been shown to be correlated with the integrated responses of tissue molecular signalling pathways to endurance exercise.
In a similar manner, the degree of inflammatory response and production of reactive oxygen and nitrogen species (RONS) to exercise mediate favourable adaptations. Inter-individual variations in redox status has been shown to determine the ability to adapt to exercise training. However, unlimited increase in response does not necessarily produce a better outcome. An over response to exercise in these signalling pathways, hinders adaptation.
Exercise promotes bone adaptation in terms of bone material, structure and muscle action. Paracrine crosstalk occurs between muscle and bone. Muscle myokines and insulin like growth factor 1 (IGF1) favour bone formation, whilst inflammatory molecules, such as interleukin 6 (Il-6) released during muscle contractions, favour bone reabsorption. The balance between these opposing processes determines whether bone remodelling is effective, or whether bone stress reactions occur over a pathological continuum. These responses and adaptations occur on the background of lifespan Endocrine environment, which impacts the outcome.
The gut microbiota support the regulation of inflammation at the local and systemic level. Furthermore the communication between the gut microbiota and mitochondria has been described as an important interaction in facilitating adaptive responses to exercise. Mitochondria are organelles crucial for production of ATP, as well as RONS. The gut microbiota are involved in mitochondrial biogenesis by regulating key mitochondrial transcriptional factors and enzymes . Furthermore, the metabolites of the gut microbiota such as short chain fatty acids, modulate the inflammatory effects of mitochondrial oxidative stress. Conversely genetic variants in the mitochondrial genome could impact mitochondrial function and thus the gut microbiota in terms of composition and activity.
The gut microbiota have a role in regulating intestinal permeability. Leaky gut is where epithelial integrity is lost at the tight junctions between cells in the gut lining. Leaky gut can occur in gut dysbiosis and also following endurance exercise where re-perfusion injury produces acute hyper-permeability. In these instances, increased gut permeability augments the antigen load and causes increased systemic inflammation and potentially can trigger autoimmune disease. This demonstrates that an excessive inflammatory response to exercise can hinder positive adaptation
Metabolic flexibility, the ability to respond and adapt to changes in metabolic demand, is enhanced with exercise training through these autocrine, paracrine and Endocrine mechanisms. Metabolic flexibility supports energy availability and fuel selection during exercise. Exercise mimetics, such as artificial metabolic modulators, have been reported to up-regulate gene expression to shift metabolism to fat oxidation in exercising muscle. This would potentially extend the limit of endurance exercise. However this “short cut” to adaptation favouring improved sport performance is illegal, with such molecular ligands on the World Anti-Doping Agency (WADA) banned list.
Hierarchy of control
There is a hierarchy of control in modulating multi-system adaptations to exercise. The Endocrine system is key. Exercise per se produces an Endocrine response, for example exercise is a key stimulus for growth hormone release via the hypothalamus, the neuroendocrine gatekeeper. Growth hormone supports the anabolic response to exercise. In addition, the Endocrine milieu during the lifespan has an impact on response and adaptations to exercise. Any disruption in the Endocrine system hinders adaptive changes. Endocrine dysfunction may occur as a result of non-integrated periodisation of exercise/nutrition and recovery as seen in relative energy deficiency in sports (RED-S). Dysfunction can also occur due to an Endocrine pathology.
Changes in external stimuli, such as exercise and nutrition, produce internal responses on autocrine, paracrine and Endocrine levels. These molecular signalling pathways drive adaptive changes through integrated, network effects. However any imbalances in these interactive responses can hinder desired adaptive changes and even result in negative maladaptive outcomes to exercise training.
Keay N, Logobardi S, Ehrnborg C, Cittadini A, Rosen T, Healy ML, Dall R, Bassett E, Pentecost C, Powrie J, Boroujerdi M, Jorgensen JOL, Sacca L. Growth hormone (GH) effects on bone and collagen turnover in healthy adults and its potential as a marker of GH abuse in sport: a double blind, placebo controlled study. Journal of Endocrinology and Metabolism. 85 (4) 1505-1512. 2000.
Sports Endocrinology – what does it have to do with performance? Dr N.Keay, British Journal of Sport Medicine
Balance of recovery and adaptation for sports performance Dr N.Keay, British Association of Sport and Exercise Medicine
Inflammation: Why and How Much? Dr N.Keay, British Association of Sport and Exercise Medicine
Clusters of Athletes – A follow on from RED-S blog series to put forward impact of RED-S on athlete underperformance, Dr N.Keay, British Association of Sport and Exercise Medicine
Optimal Health: For All Athletes! Part 4 – Mechanisms, Dr N.Keay, British Association of Sport and Exercise Medicine
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Exosomes as Mediators of the Systemic Adaptations to Endurance Exercise Cold Spring Harbor Perspectives in Medicine
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Adaptations to endurance training depend on exercise-induced oxidative stress: exploiting redox inter-individual variability, Acta Physiologica
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Leaky Gut As a Danger Signal for Autoimmune Diseases, Frontiers in Immunology
Metabolic Flexibility in Health and Disease Cell Metabolism
PPARδ Promotes Running Endurance by Preserving Glucose, Cell Metabolism
By Renee Mc Gregor
It’s the nature of the society we live in; many of us believe that we can change one aspect of our lives without in impacting another.
Athletes and dancers in particular will always be in search of that golden nugget that is going to enhance performance, many forgetting that what information is available may not be relevant to them.
There is a marked difference between Performance Nutrition and “Healthy Eating” guidelines. In many cases, if an athlete tried to follow the principles of nutrition for health, they may find themselves at risk of low energy availability. A diet high in fruits and vegetables is ideal for those individuals who are generally sedentary of who may meet the recommended “moderate” activity levels but is it suitable for a dancer who rehearses and practices 4-6 hours a day?
On average we go from utilising 1 calorie per minute at rest to up to 8 calories per minute when running at a moderate intensity. A diet high in fruit and vegetables provides antioxidants, vitamins, mineral and fibre; while these are important for a healthy balanced diet, in athletes the bulk and volume often means they displace more relevant nutrients such as energy and protein.
So what can seem like a good idea, a change in nutritional intake or an increase in training, can also be the first stages on the slippery slope to longer term health consequences.
Athletes and Dancers tend to be a certain personality type – determined, focused, compulsive, obsessive and self critical. This is not a bad thing; it is of course these traits that help them to achieve success. However, if these same traits are not managed well, they can also become their Achilles heel. The drive for success becomes something that is never fulfilled; the harder they try through training and restrictive eating, they never get to the point where they are satisfied and the more compulsive their behaviours becomes.
What started out as a “way of improving” soon results in psychological and physical consequences. When the body is under “stress” levels of cortisol rise; when this is chronic, it prevents the pituitary gland from working effectively, leading to hormonal disturbances that have serious negative consequences to performance. Similarly, the more obsessive and restrictive an individual becomes, it affects not only the levels and transmission of neurotransmitters but also has shown to structurally affect the brain, making it more and more difficult to make decisions. There is also a heightened sense of anxiety- it is this anxiety that leaves an individual feeling physically and mentally uncomfortable. In an attempt to control and contain these emotions, the individual’s behaviours become even more rigid and controlled.
The mind and the body are intrinsically linked. When energy availability is low, we know that it will reduce testosterone and oestrogen. These sex hormones have multiple roles from bone to heart health but also the production of serotonin, the feel good neurotransmitter in our brain. So when testosterone and oestrogen are at low levels, this also results in less serotonin being produced, leaving the individual low in mood. Comparatively, we know that exercise increases are level of dopamine, another feel good neurotransmitter. So its not surprising then that those athletes that are low in energy, will find it necessary to continue to train in order to boost their “well being”. The difficulty of course is that over stimulation of any neurotransmitter will impact another role within the brain. So flooding the brain with dopamine, causes a dysfunction of the midbrain resulting in the salience part of the brain becoming affected; that is the part of the brain that is involved in decision making and evaluating threat. This is why an athlete cannot see that their behaviours are actually detrimental to their health.
It is possible to see how being in a competitive environment, while necessary for human productivity, can also give rise to behaviours which if not managed well can result to a slippery slope towards a dysfunctional relationship with food and training.
Renee McGregor BSc (hons) PGDIP (DIET) PGCERT(sportsnutr) RD SENr
Sports and Eating Disorder Specialist Dietitian
Author of “Orthorexia” “Training Food” and “Fast Fuel” books
Co Founder of #TRAINBRAVE, a campaign launched to raise awareness of eating disorders and relative energy deficiency in sports (REDs), highlight risks, and change attitudes within endurance sports.