Cardiovascular Drift Response Over Two Different Constant-load Exercises In Healthy Non-athletes. Case Study.

Abstract

Cardiovascular drift (CV-d) is a steady increase in heart rate (HR) over time while performing constant load moderate intensity exercise (CME) > 20 min. CV-d presents problems for the prescription of exercise intensity by means of HR, because the work rate (WR) during exercise must be adjusted to maintain target HR, thus disturbing the intended effect of the exercise intervention. It has been shown that the increase in HR during CME is due to changes in WR and not to CV-d. PURPOSE: We aimed to investigate whether, indeed, the CV-d in healthy young people exercising at the WR corresponding to the lactate individual anaerobic threshold (IAT) determined in two different cardiorespiratory exercise test (CPT), was related to the WR difference. METHODS: Seven participants (30 ± 3 years old, 1.75 ± 0.1 m., 74.6 ± 12.8 Kg.) performed on different days two CPT with a WR increase of 20 Watts (W) every one or three minutes until exhaustion. The WR corresponding to the IAT was determined during these tests. The participants then performed two CME with a WR corresponding to the IAT. HR and blood lactate (La) were continuously measured during all tests. A comparison between CPTs and CMEs were made using a paired t-test. A one-way ANOVA repeated measurements was used to compare La values during the CME. RESULTS: VO2max (36.9 ± 59 vs. 35.6 ± 5.7 ml·Kg-1·min-1; p > 0.05), maximal HR (181 ± 9 vs. 178 ± 11 bpm; p = 0.3), and peak La (8.7 ± 1.6 vs. 7.8 ± 1.6; p = 0.1) did not differ between CPTs. Maximal power output (271 ± 80 vs. 223 ± 75 W; p < 0.001) and WR at the IAT (164 ± 63 vs. 137 ± 45 W; p > 0.01) were different between CPTs. La between CMEs and minutes 10 and 30 were not different (3 ± 0.4 vs. 3.3 ± 0.5; p = 0.1). One-CME mean HR was 157 ± 12 bpm with an increase of 8 ± 4 bpm between minutes 10-30. Three-MCE HR was 147 ± 14 bpm and the HR increased by 9 ± 7 bpm between minute 10-30. Only a difference in HR between the two CME was found (p = 0.009) whereas there was no difference in the HR change between minute 10-30 (p = 0.7). CONCLUSION: In this case study, the CV-d was not significantly different between the two CMEs (One-IAT and Three-IAT) despite a significant difference in the amount of WR between CMEs (26 ± 19). Other factors aside from the WR like an increase in peripheral blood flow, hyperthermia, plasma volume reduction, catecholamine levels, and training status play a role in the CV-d phenomenon.