Impact of high-intensity and high-volume exercise on short-term perturbations in the circulating fraction of different cell types.

Background: High-intensity training (HIT) can improve endurance performance and VO2max more effectively than high-volume training (HVT). Hence, the implementation of HIT protocols such as 4x30 s "all-out" and 4x4 min at 90-95% VO2max is currently existent in various sports. However, there is limited awareness of the acute changes in blood cell count following these protocols. Therefore, the purpose of the study was to examine the acute effects on circulating leukocyte differential count (LDC) by comparing the two HIT interventions with a single HVT intervention.

Methods: Twelve healthy triathletes/cyclists (VO2peak: 64.3±9.7 mL·kg-1·min-1) participated in the study. Subjects performed: 1) a two-hours low-intensity exercise at an intensity of 55% peak power output (PPO); 2) 4x4 min interval bouts at an intensity of 90-95% PPO; 3) 4x30 s "all-out". Blood samples were taken immediately before exercise (pre) and 0', 30', 60' and 180' postexercise. Biphasic leukocyte enumeration was different between both HIT protocols and nonexistent after high-volume exercise.

Results: Data revealed significant time and intervention effects for leukocytes, lymphocytes and neutrophils. After 4x30 s lymphocytes were significantly higher 0´ postintervention compared to 4x4 min and high-volume exercise. Furthermore, concentrations of leukocytes and neutrophils were significantly higher after the "all-out" protocol compared to 4x4 min at 180' postexercise.

Conclusions: The results suggest that 4x30 s result in larger short-term perturbations in the circulating fraction of leukocytes compared to 4x4 min, which might be associated with increased hormonal and metabolic stress responses after 4x30 s.