Acute Erythrocyte Aggregation Responses to a Shuttle Run Exercise in a Cold Chamber at −10 °C in Healthy Young Men

Background: Exercise in the cold is an attractive option for many athletes. Erythrocyte aggregation, as one of the main rheological parameters, constitutes an important indicator of microcirculation and oxygen transport capacity in the human body. Acute exercise and environmental cold may alter erythrocyte aggregation. We compared immediate hematological, aggregation, metabolic, and hormonal responses to progressive shuttle run exercise in a cold chamber and outdoors. Methods: This exploratory parallel-group analysis included 30 young healthy male students allocated to exercise in a climatic chamber at −10 °C (n = 15) or outdoors at 18 °C (n = 15). Blood was collected before and immediately after exercise. Group × time interactions were assessed using repeated-measures ANOVA and within-group comparisons used Bonferroni adjustment. Results: Erythrocyte amplitude of aggregation (AMP) showed a significant group × time interaction (p = 0.0014). In the paired analysis, the between-group difference in AMP change was −3.24 au (pointwise 95% CI −5.12 to −1.36). Lactate showed a nominal interaction (p = 0.016). Within the experimental group, red blood cell count, hemoglobin, hematocrit, mean corpuscular volume, aggregation index (AI) and lactate increased, whereas AMP and aggregation half-time (T½) decreased (all p < 0.001). Estimated plasma-volume change did not differ significantly between settings. Conclusions: Exercise in the cold-chamber setting was associated with a greater reduction in the optical aggregation amplitude. Further studies are needed to clarify the contribution of temperature and the physiological significance of these changes.