Abstract
Competitive swimming requires high training load cycles including consecutive sessions with little recovery in between which may contribute to the onset of fatigue and eventually illness. We aimed to investigate immune changes over a 7-month swimming season. Fifty-four national and international level swimmers (25 females, 29 males), ranging from 13 to 20 years of age, were evaluated at rest at: M1 (beginning of the season), M2 (after the 1st macrocycle’s main competition), M3 (highest training load phase of the 2nd macrocycle) and M4 (after the 2nd macrocycle’s main competition) and grouped according to sex, competitive age-groups, or pubertal Tanner stages. Hemogram and the lymphocytes subsets were assessed by automatic cell counting and by flow cytometry, respectively. Self-reported Upper Respiratory Symptoms (URS) and training load were quantified. Although the values remained within the normal range reference, at M2, CD8+ decreased (M1 = 703 ± 245 vs. M2 = 665 ± 278 cell μL−1; p = 0.032) and total lymphocytes (TL, M1 = 2831 ± 734 vs. M2 = 2417 ± 714 cell μL−1; p = 0.007), CD3+ (M1 = 1974 ± 581 vs. M2 = 1672 ± 603 cell μL−1; p = 0.003), and CD4+ (M1 = 1102 ± 353 vs. M2 = 929 ± 329 cell μL−1; p = 0.002) decreased in youth. At M3, CD8+ remained below baseline (M3 = 622 ± 245 cell μL−1; p = 0.008), eosinophils (M1 = 0.30 ± 0.04 vs. M3 = 0.25 ± 0.03 109 L–1; p = 0.003) and CD16+56+ (M1 = 403 ± 184 vs. M3 = 339 ± 135 cell μL−1; p = 0.019) decreased, and TL, CD3+, and CD4+ recovered in youth. At M4, CD19+ were elevated (M1 = 403 ± 170 vs. M4 = 473 ± 151 cell μL−1; p = 0.022), CD16+56+ continued to decrease (M4 = 284 ± 131 cell μL−1; p < 0.001), eosinophils remained below baseline (M4 = 0.29 ± 0.05 109 L–1; p = 0.002) and CD8+ recovered; monocytes were also decreased in male seniors (M1 = 0.77 ± 0.22 vs. M4 = 0.57 ± 0.16 109 L–1; p = 0.031). The heaviest training load and higher frequency of URS episodes happened at M3. The swimming season induced a cumulative effect toward a decrease of the number of innate immune cells, while acquired immunity appeared to be more affected at the most intense period, recovering after tapering. Younger athletes were more susceptible at the beginning of the training season than older ones.
Highlights
It is generally acknowledged that the immune system may experience a functional reduction when exposed to successive psychological and physical stressful stimulus, such as the competitive training process (Walsh et al, 2011)
The number of studies assessing the effect of long-term training periods on the chronic response of leukocytes and subsets in athletes of different sports such as swimming (Gleeson et al, 1995; Mujika et al, 1996; Morgado et al, 2012, 2017; Rama et al, 2013; Teixeira et al, 2014), running (Denguezli et al, 2008), basketball (Brunelli et al, 2014), volleyball (Dias et al, 2011), and soccer (Suda et al, 2013; Del Giacco et al, 2014) is scarce, especially if we consider articles that assess the incidence of Upper Respiratory Symptoms (URS)
When swimming training is concerned, the length and seasonality of the training programs are rather consistent between squads and coaches
Summary
It is generally acknowledged that the immune system may experience a functional reduction when exposed to successive psychological and physical stressful stimulus, such as the competitive training process (Walsh et al, 2011). In order to attain high level performances, endurance athletes, such as swimmers, undertake large periods of intense training with short recovery periods (Aubry et al, 2014). These training conditions aim to stimulate adaptive mechanisms related to metabolic, hormonal, circulatory and respiratory responses to improve performance. If subsequent extra pressure is generated, a state characterized by substrate depletion and hormonal and immune functions disturbances may arise, from which athletes often report infection episodes after hard training periods (Gleeson, 2007; Cordova et al, 2010; Dias et al, 2011; Morgado et al, 2012; Gleeson and Williams, 2013; Rama et al, 2013). It seems that longterm intensified training can affect the number of circulatory innate immune cells
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