Leukocytes and lactate responses to cycling and running at the same target heart rate

Heart Rate (HR) is widely used for erobic exercise intensity prescriptions and/or studies of exercise training. It is often assumed that exercising at a given HR results in similar physiological response, regardless of exercise modality. This study aimed to gauge cellular immune mobilization to submaximal exercise at a given target HR on a cycle ergometer (CE) and treadmill (TM). Thirteen healthy male adults (23.2 +/- 3.5 y.o) completed 4 laboratory visits. Participants performed two graded exercise tests to exhaustion on CE and TM and two 30-min constant exercise challenges at 70% HR reserve on CE or TM in random order. Rating of Perceived Exertion (RPE) was recorded every 5 min, and blood was drawn before and after exercise to measure leukocytes subpopulation levels, lactate, and IL-6. HR was successfully "clamped" during the exercise in CE and TM (CE 156.7 +/- 1.1; TM 159.3 +/- 1.6 bpm). Cycling was perceived as more strenuous than running and was accompanied by a greater increase in lactate post-exercise (p < 0.0001; 6.2 +/- 0.3 vs. 2.9 +/- 0.3 mmol/L). IL-6 and leukocytes subpopulations were significantly elevated post-exercise (p < 0.003) with no difference between exercise modalities (monocytes; CE 57.6% TM 61.2%, granulocytes; CE 41.37%, TM 50.1%, lymphocytes; CE 91.03%, TM 78.8%). The findings revealed that HR is not sufficient in and of itself to fully assess the metabolic stress associated with a given exercise modality. However, despite different metabolic and subjective stress, the IL-6 and leukocyte counts relative changes were similar in the two modalities.