HIIT Induces Stronger Shifts within the Peripheral T Cell Compartment Independent of Sex.

Acute exercise induces changes within the T-cell compartment, especially in cytotoxic CD8⁺memory subsets, depending on exercise intensity and duration. It is unclear whether exercise-induced changes in major T-cell subsets differ in response to acute high-intensity interval training (HIIT) or moderate-intensity continuous training (MICT) and whether sex-specific effects exist. Twenty-four recreationally active runners (females: n=12, 27.8±4.1years, 54.4±4.6 ml*kg^-1*min^-1; males: n=12, 31.6±3.8years, 58.9±7.7 ml*kg^-1*min^-1) participated in this randomized controlled crossover study, and conducted an energy- and duration-matched HIIT and MICT session. Blood was sampled before (T₁), immediately (T₂) and 1 h after exercise (T₃). Flow cytometry was used to identify T-cell populations. HIIT decreased the proportion of CD8⁺T-cells more pronounced at T₃ compared to MICT (p=0.007), induced a significantly stronger increase in the CD8⁺effector memory (T_EM) cell proportion at T₂ (p=0.032), and decreased CD4⁺central memory proportion more pronounced at T₂ (p=0.029). A decrease below baseline CD8⁺T_EM proportion at T₃ was observed only after HIIT (p<0.001). No interaction effects between sexes were revealed. Taken together, HIIT represents a more potent stimulus to induce shifts mainly within the cytotoxic CD8⁺T-cell compartment, thereby giving implications to investigate the role of HIIT on the cell´s effector phenotype and function in more detail.