6.1 Allergic athletes and susceptibility to infections
An increasing proportion of young athletes are atopic, i.e. show signs
of IgE-mediated allergy which is, along with the sport event, a major
risk factor for asthma and respiratory symptoms in athletes (104,105).
The relative importance of allergy is growing, also because pollen
exposure may become more prolonged and intense with global warming
(106). A mixed type of eosinophilic and neutrophilic airway inflammation
seems to affect especially swimmers, ice-hockey players, and
cross-country skiers (107). The inflammation may represent a
multifactorial aggression, in which both allergic and irritant
mechanisms play a role. In allergic athletes, high level competition
seems to exacerbate at least some components of the allergic immune
response, such as airway hyperresponsiveness and airway inflammation.
The question remains about how excessive exercise affects the Th1/Th2
balance. If exercise drives a Th2 response then a more difficult to
control phenotype in the elite allergic athlete may be expected.
Growing points and areas for developing research Immunological changes associated with exercise form a potentially
promising field of research with many gaps to be filled. Detailed
assessment of microbiome involved in pathogenesis of respiratory
symptoms in athletes is one of the most obvious and evident challenges
that exercise immunologists and sports scientists are currently
confronted with. Studies looking at the impact of exercise or physical
activity on susceptibility to infection varied widely in respect to
subjects, exercise load and methods (93). Further elucidation of
processes lying behind respiratory symptoms without an ascertained
pathogen is one of considerable research gaps. In this aspect, few
studies have so far addressed the impact of regular chronic exercise
training on humoral and cellular immunity in humans. Infection-like
symptoms in subjects in whom no pathogen can be identified are not
fully explained regarding underlying inflammatory mechanism,
therefore, the role of pre-existing silent or latent infections should
be taken into consideration in future studies.
Over last 18 months, the COVID-19 pandemics created challenges for
medical professionals irrespective of specialty (108). In the context
of exercise training, key issues to be addressed are:
- Influence of regular training of different intensities on
susceptibility to SARS-CoV-2 infection (109)
- Influence of COVID-19 infection on sports performance (110,111)
- Maintainig immune health during restrictions caused by pandemic and
temporarily limited access to sports facilities (112)
- Return to regular exercise after COVID-19 infection (113)
Establishing a uniform definition of “elite athlete” will contribute
to a more comparable and straightforward interpretation of data coming
from different studies and settings. Hence, issues to be tackled
include:
- Are the athletes who show more “immunodepression” more prone to
URTIs during the weeks following exercise?
- Which are the clinically relevant outcomes to assess and predict
meaningful exercise-induced immunodepression?
- Is downregulation of non-specific immunity after intense exercise a
normal protective response, with mild immunodepression being an
attempt to limit inflammation?
- When should the exercise-associated changes in non-specific immunity
be considered pathological?
- What are the differences between healthy and illness prone athletes in
the above-mentioned context?
- What is the efficacy, if any, of nutritional or pharmaceutical
interventions as countermeasures to URTI symptoms?
In conclusion, exercise - depending on its pattern, intensity and
environmental conditions - modifies various aspects of immune
response. The degree of clinical relevance of these modifications and
the ways they may impact the sports performance remain promising field
for future research.Figure 1A J-shaped model describing relationship between exercise load and the
risk of URTI. Modified after NiemanFigure 2An S-shaped relationship between training load and infection rate,
proposed by Malm (modified after )
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