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Tricia L. Hart, CSCS – n/a, n/a

Eliott Arroyo, MS – PhD Candidate, Kent State University

Emily C. Tagesen – Graduate Assistant , Kent State University

Brandon A. Miller, CSCS – Graduate Student, Kent State University

Adam R. Jajtner


PURPOSE: To compare the effects of high-intensity interval training (HIIT) and moderate-intensity continuous training (MCT) on leukocyte subset populations. METHODS: Recreationally active men (n=3; 21.3±3.5 yrs; 182.8±6.3 cm; 11.2±5.8 %BF; 79.4±8.7 kg; 44.1±3.2 ml·kg-1·min-1) completed a maximal graded exercise test (VO2max) and two exercise trials (HIIT and MCT) in a randomized, counterbalanced fashion on a cycle ergometer. HIIT consisted of fifteen 90-second bouts at 85% VO2max interspersed with 90-second active recovery periods. MCT consisted of a single continuous bout at 65% VO2max. Each trial lasted 53 minutes, including a 5-minute warm-up and a 3-minute cool-down. Blood was collected before (PRE), immediately post (IP), 30 minutes (30M), 2 hours (2H), 6 hours (6H) and 24 hours (24H) post-exercise. Leukocyte count (WBC), lymphocyte number and ratio (LY# and LY %), monocyte number and ratio (MO# and MO%) and granulocyte number and ratio (GR# and GR%) were analyzed via an automated hematology analyzer. Changes were assessed using a two factor (time × trial) within-subjects repeated measures ANOVA. All data were confirmed for normality via a Shapiro-Wilk test.  RESULTS: A significant interaction between trials was observed in WBC (F=4.59, p=0.020, η2p=0.70). During HIIT, significant increases in WBC were observed from PRE (3.75±1.15 103∙μL-1) to IP (8.08±1.76 103∙μL-1; p=0.013), 2H (7.42±1.26 103∙μL-1; p =0.002), and 6H (6.51±0.80 103∙μL-1; p =0.006) .  Additional increases were observed from 30M (4.27±1.26 103∙μL-1) to 2H (p=0.026) and 6H (p=0.035). During MCT, WBC increased from PRE (3.98±1.15 103∙μL-1) to 2H (6.81±1.16 103∙μL-1; p=0.014) and 6H (6.49±1.16 103∙μL-1; p=0.003). No differences were observed from PRE to IP (5.24±0.069 103∙μL-1), 30M (3.82±0.24 103∙μL-1) or 24H (3.66±0.54 103∙μL-1). A significant interaction between trials was observed for LY# (F=22.686, p< 0.001, η2p = 0.919). During HIIT, LY# increased from PRE (1.67±0.13 103∙μL-1) to IP (3.33±0.61 103∙μL-1; p=0.032), while decreases were observed relative to IP at 30M (1.34±0.16 103∙μL-1; p=0.021), 2H (1.43±0.10 103∙μL-1; p=0.040) and 24H (1.58±0.10 103∙μL-1; p=0.045). No differences were observed between PRE, 30M, 2H, 6H (2.13±0.09 103∙μL-1), or 24H. During MCT, LY# increased from 30M (1.57±0.23 103∙μL-1) and 2H (1.72±0.44 103∙μL-1; p=0.043) to 6H (2.42±0.42 103∙μL-1; p=0.044).  No differences were observed between PRE (2.06±0.22 103∙μL-1), IP (2.49±0.26 103∙μL-1), 30M, 2H and 24H (1.56±0.10 103∙μL-1). With all trials combined, significant time effects were observed for LY% (F=7.668, p=0.003, η2p = 0.793), MO% (F=5.352, p=0.012, η2p = 0.728), GR% (F=8.224, p=0.003, η2p = 0.804) and GR# (F=24.109, p< 0.001, η2p = 0.923), though no differences were observed between conditions (p > 0.05). CONCLUSION: Data suggest that HIIT stimulates WBC and LY# more than MCT at IP. Additionally, LY# may be suppressed at 30M and 2H in HIIT, but not MCT.  PRACTICAL APPLICATIONS: As interval training has been shown to be effective with a lessened duration, it is becoming popular among coaches and athletes, as well as the general population. Though further research is warranted, the immunosuppressive effects observed following HIIT suggest that intensity may have a greater effect than volume on the immune response to exercise.  Moreover, coaches may want to consider the potential immunosuppressive effects of HIIT training. This study was funded via an NSCA-Foundation Doctoral Research Grant.


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