There is a substantial body of evidence that indicates that there may be a causal relationship between stress and intestinal barrier dysfunction, due mainly to the systemic and peripheral release of corticotropin-releasing factor (Rodiño-Janeiro et al, 2015). Recent evidence suggests that IgG mediated food intolerance as a result of intestinal barrier dysfunction is associated with impaired physical performance (Kostic-Vucicevic et al, 2017) therefore, it is vital to consider the impact that chronic stress may play in this area.
From an athlete’s perspective, avoiding chronic stress is therefore key to promoting improved digestive function, oral tolerance and ultimately achieving greater physical performance gains. In terms of training specifically, since overtraining is a form of chronic stress, this highlights the importance of being mindful with regards to the avoidance of overtraining in an individual’s physical programme. This can be achieved by ensuring that sessions are of the appropriate intensity, and that they include sufficient rest and recovery between sessions.
Aside from the influence that chronic stress can have upon the digestive tract and immune system, chronic stress can also be detrimental to the health and optimal functioning of the adrenals themselves, thus negatively affecting physical performance from another angle.
Overtraining and the adrenal glands
The adrenal glands are vital to human health and wellbeing. For athletes, it is essential that they are functioning optimally to enable them to sustain the quantity and intensity of workload that their bodies must endure (Brooks and Carter, 2013).
In essence, there is a point of diminishing returns (which will be specific for each individual), where chronic stress has been linked to adrenal insufficiency. Overtraining across an extended period of time, can result in adrenal depletion and an Addison-Type overtraining syndrome, where the adrenal glands are no longer able to maintain proper hormone levels (Brooks and Carter, 2013).
Chronic stress, cortisol dysfunction and sporting performance
If an individual’s stress response becomes chronic, this causes cortisol levels to stay continually high (Hannibal and Bishop, 2014). DHEA (dehydroepiandrosterone), another hormone produced by these glands, effectively works as an antagonist to cortisol, and protects against the negative effects of cortisol (McNelis et al, 2013). Therefore, if DHEA levels fall, this protective mechanism would also be expected to decrease, especially if cortisol remains high. This is one of the reasons that the Cortisol:DHEA ratio is thought to be so significant. Prolonged stress has been associated with a reduction in DHEA (Izawa et al, 2012). This is perhaps due to cholesterol (the precursor to both hormones) being diverted away from DHEA production and instead towards the cortisol synthesis pathway during periods of increased stress. This is otherwise known as the pregnenolone steal (Brook and Marshall, 1996).
If the stressor, for example overtraining, is not removed at this point, then the adrenal glands may become even more overworked, potentially inhibiting cortisol and DHEA production. Stress-induced cortisol dysfunction can result in bone and muscle breakdown as well as fatigue (Hannibal and Bishop, 2014), which further compounds the problem by hindering post-exercise recovery. This would potentially make athletes more susceptible to injury and illness, thus jeopardising their fitness and performance gains.
It is therefore important to assess the balance of the adrenal glands, so that an individual’s training program can be adapted, and treatment strategies put in place, to ensure that they are supported before reaching the fatigued state described above. In addition, this will help identify any other underlying stressors such as, lifestyle habits, toxicity, infections and nutritional issues.
Adrenal function testing and supporting the adrenals
Reducing endocrine imbalance through diet and lifestyle changes, enables faster recovery and regeneration post training (Stachowicz and Lebiedzinska, 2009). In addition, and perhaps more importantly, avoiding the effects of chronic stress on these glands may mean that no time is required away from training.
Testing cortisol and DHEA levels can therefore be an extremely useful adjunctive diagnostic tool for athletes as it can help to identify whether their adrenals are functioning optimally. This in turn will help determine if there is a need for the individual to implement a tailored stress management strategy to help ensure optimum performance.