Leukocyte response to repeated sprint exercise: Differences between adolescent and adult athletes

Repeated sprint exercise (RSE) can significantly affecting leukocytes dynamics, influenced by fitness, lifestyle, and biological maturation (BM), especially in adolescents.

This experimental trial examined RSE effects on leukocyte responses in 34 male-athletes (18 adolescents, age = [12.9 ± 1.1] years; 16 adults, age = [22.5 ± 2.2] years). Participants performed 3 sets of 6 sprints (35 m with 10 s of passive rest and 5 min between sets), with blood samples collected before, immediately after, 2 h, and 24 h after-RSE. Leukocyte levels were analyzed microscopically and via leukogram, and adolescents' BM was assessed using peak-height-velocity (PHV). Statistical analyses included Friedman and Mann-Whitney U tests.

Total leukocyte counts increased immediately after and at 2 h after-RSE in both groups (p < 0.00156). Lymphocytes increased immediately after-RSE (absolute and relative, p < 0.00156). Absolute segmented neutrophils and the neutrophil-to-lymphocyte-ratio (NLR) peaked at 2 h (p < 0.001). Large granular lymphocytes (LGLs) increased only immediately after-RSE (p < 0.00156). Absolute and relative eosinophils decreased at 2 h and rose again 24 h (p < 0.00156). Regarding the condition factor, 2 h after-RSE adults showed higher levels of NLR and segmented neutrophils compared to adolescents (p < 0.0001); while adolescents were higher in relative lymphocyte values (p < 0.0001). Eosinophil levels were higher in adolescents 2 h after-RSE, extending up to 24 h after-RSE (p < 0.0001). In PHV-based sub-analyses, for the time factor, circum-PHV (circum = during-PHV)individuals showed more evident responses in total leukocytes, absolute lymphocytes, LGLs, and segmented neutrophils (p < 0.00156), reflecting greater immunological sensitivity to exercise. No significant condition-related differences were observed between pre-and circum-PHV subgroups.

It is concluded that RSE promotes transient immune mobilization, more pronounced in adults, and modulated by the stage of biological maturation.