Correlation Properties Of HRV During Marathon Racing In Recreational Runners: Potential Biomarker Of Organismic Demands

Abstract

PURPOSE: Scant information exits regarding cardiovascular response and regulation in real-world endurance training/competition. Although there is data describing behavior of heart rate (HR) and HR variability (HRV) during actual events, the specific linear indexes studied have been less than optimal for assessment of real-time exercise intensity due to a lack of appreciable changes during exercise. In this context, non-linear HRV analysis is a promising approach for internal load monitoring of organismic demands related to external load markers such as intensity, cadence and duration., leading to insights in complex regulation during endurance exercise. The present study is the first to examine the influence of a marathon race on non-linear dynamics of HRV to assess its feasibility as a potential biomarker during endurance exercise. METHODS: Eleven male recreational runners performed a marathon race on an almost flat profile. During the race, HR time series was recorded continuously. HRV time-domain measurements and correlation properties using short-term scaling exponent alpha1 of Detrended Fluctuation Analysis (DFA-alpha1) were calculated. RESULTS: All runners achieved a mean total time of 3:10:22 ± 0:17:56 h:min:sec with a blood lactate concentration of 4.04 ± 1.12 mmol/l after finishing the race. Comparing the beginning to the end segment of the marathon race, significant increases could be found for km split time (p < .001, d = .934) and for HR (p = .010, d = .804). Significant decreases could be found for meanRR (p = .013, d = .798) and DFA-alpha1 (p = .003, d = 1.132). CONCLUSIONS: DFA-alpha1 showed wide dynamic range throughout the race consisting of both uncorrelated and anti-correlated values. Lactate was consistent with sustained high intensity exercise when measured at the end of the event. Despite the gradual slowing of km split times especially past the midpoint, DFA-alpha1 continued to fall to values seen in the highest intensity domain during incremental exercise testing in agreement with lactate assessment. Therefore, the discrepancy between the reduced running pace with that of the decline of DFA-alpha1, demonstrate the benefit of using this dimensionless HRV index as a potential biomarker of internal load during endurance exercise.