Exercise effects on immunity are highly dependent on exercise intensity, duration, and frequency. Purpose: Because neutrophils play an essential role in innate immunity, we investigated whether acute severe exercise (ASE) and chronic moderate exercise (CME) differentially regulate human neutrophil functions. Methods: Thirteen sedentary young males underwent an initial ASE (pedaling on a bicycle ergometer with increasing loads until exhaustion), and they were subsequently divided into exercise (n = 8) and control groups (n = 5). The exercise group underwent 2 months of CME (pedaling on the ergometer at a moderate intensity for 30 min each day) followed by 2 months of detraining. The control group was abstained from regular exercise during these 4 months. Additional ASE paradigms were performed every month (in the exercise group) or every 2 months (in the control group). Neutrophils were isolated from blood specimens drawn at rest and immediately after each ASE for assaying chemotaxis, phagocytosis, citrate synthase activity, and mitochondrial membrane potential (ΔΨm). Additional blood specimens were drawn from the exercise group before and immediately after the first bout of CME to determine the acute moderate exercise (AME) effects on neutrophil functions. Results: The study's results are the following: 1) the initial ASE enhanced chemotaxis and induced ΔΨm depolarization; 2) AME did not influence any measured parameter in neutrophils; 3) CME increased chemotaxis, phagocytosis, citrate synthase activity, and ΔΨm; 4) the CME effects remained after detraining except phagocytosis; and 5) the ASE effects disappeared after CME and were partially restored after detraining. Conclusions: ASE and CME differentially affected neutrophil functions, whereas AME was ineffective. Moreover, the fact that CME improves neutrophil functions may partially explain why physically active subjects have a low risk of infection.
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