Leukocyte and Lactate Responses to Different Modes of Exercise at the Same Target Heart Rate

Heart Rate (HR) is widely used for exercise intensity prescriptions and/or studies of exercise training. It is often assumed that exercising at a given HR results in similar metabolic stress, regardless of the mode of exercise. PURPOSE: To gauge the leukocyte and lactate responses following a submaximal exercise at an equivalent target HR on cycle ergometer (CE) and treadmill (TM). METHODS: Six healthy male adults (25.4 ± 3.2 y.o) completed 4 laboratory visits. Participants performed a progressive exercise test to exhaustion on CE and TM. On subsequent separate days, in a randomized order, participants performed a 30-min constant exercise challenge at 70% HR reserve (HRR) on CE or TM. Borg’s Rating of Perceived Exertion (RPE) was recorded every 5 min. Blood was drawn before and immediately after the 30-min exercise. Paired t-test was used to evaluate within-person differences (before/after exercise) & between modes. Due to the small sample size, effect sizes were also calculated. RESULTS: We successfully “clamped” HR during the exercise in CE and TM (CE, 154.8 ± 0.7; TM 156.8 ± 0.8 bpm). During the first 10 minutes, all participants perceived the CE challenge as more strenuous compared to the TM (RPE; 13.9 ± 0.1 vs. 11.3 ± 0.4), with no significant difference between modes during the last 10-min (11.7 ± 0.5 vs. 12.5 ± 0.0). Immediately following the exercise, lactate was greater in CE (5.9 ± 1.4 mmol/L) vs. TM (3.1 ± 1.3, p =.032). Leukocytes were significantly elevated (p<.003) immediately after exercise for both CE and TM, with no difference between exercise modes (monocytes; CE 53.3 %, TM 62.5%, granulocytes; CE 33.5%, TM 42.7%, lymphocytes; CE 118.7%, TM 76.9%). However, a moderate effect size (d= .486) was seen for lymphocytes, with a greater increase in CE. CONCLUSION: Lactate response was lower on TM while leukocyte response was generally similar. The smaller lactate increase on TM may reflect lower reliance on anaerobic metabolism when using a larger muscle mass and/or greater lactate clearance by upper body muscles. The similar leukocyte response may reflect the fact that in both modes metabolic stress was moderate. HR is not sufficient in and of itself to fully assess the metabolic stress associated with a given mode of exercise. Supported by NIH P01HD-048721 & PERC Systems Biology Fund