A pilot study: the effect of intensity and menstrual cycle phase on exercise-induced leukocytosis in females

High-intensity exercise increases inflammation and elicits leukocytosis but may also increase infection risk. Interestingly, females have higher cell-mediated immunity than males. Sex hormones fluctuate across the menstrual cycle (MC), and the luteal phase has been linked to a more pro-inflammatory environment than the follicular phase. This study investigated whether white blood cell (WBC) count and WBC differential (i.e., neutrophils, lymphocytes, monocytes, eosinophils, and basophils) differed across two MC phases following an acute bout of exercise that varied in intensity. Eight regularly menstruating females (age = 21.6 ± 3.0; BMI = 20.9 ± 4.1 kg/m²) completed a <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mover><mml:mrow><mml:mi>V</mml:mi></mml:mrow> <mml:mo>˙</mml:mo></mml:mover> <mml:msub><mml:mtext>O</mml:mtext> <mml:mn>2</mml:mn></mml:msub> </mml:math> peak (37.8 ± 11.0 mL/min/kg) test and two 40 min cycling exercise trials (30 min of moderate intensity (%HRmax = 71.13 ± 8.5, % <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mover><mml:mrow><mml:mi>V</mml:mi></mml:mrow> <mml:mo>˙</mml:mo></mml:mover> <mml:msub><mml:mtext>O</mml:mtext> <mml:mn>2</mml:mn></mml:msub> </mml:math> peak = 49.8 ± 21.6) and ∼10 min of high intensity (%HRmax = 93.3 ± 6.7, % <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mover><mml:mrow><mml:mi>V</mml:mi></mml:mrow> <mml:mo>˙</mml:mo></mml:mover> <mml:msub><mml:mtext>O</mml:mtext> <mml:mn>2</mml:mn></mml:msub> </mml:math> peak = 75.4 ± 27.6)) 14 ± 2 days apart. Blood samples were taken pre- and post-moderate-intensity exercise (30 min), as well as immediately post-high-intensity exercise (∼40 min). Both moderate- and high-intensity exercise increased WBC counts (<i>p</i> < 0.01, (<i>d</i> = 1.11 and 1.34, respectively)). More specifically, neutrophil counts increased following both moderate (<i>p</i> < 0.05, <i>d</i> = 0.72) and high (<i>p</i> < 0.01, <i>d</i> = 0.95) exercise intensities. However, lymphocytes (<i>p</i> < 0.01, <i>d</i> = 1.15) and monocytes (<i>p</i> < 0.01, <i>d</i> = 0.99) were only elevated following high-intensity exercise. MC phase did not significantly alter WBC counts nor differentials, although there were trends observed towards greater leukocytosis at moderate-intensity exercise during the luteal phase. These results demonstrate that in some cases moderate-intensity exercise increased leukocytosis (in particular, neutrophils), while high-intensity exercise resulted in significant leukocytosis primarily as a result of increased neutrophils, lymphocytes, and monocytes. Future research should investigate this relationship in a larger sample observing inflammatory cytokines and WBC function/activity with the inclusion of a group in the early follicular phase.