Cardiorespiratory Fitness And Heart Rate Variability As Indicators Of Cardiovascular Health

PURPOSE:Greater cardiorespiratory fitness (CRF), measured as VO2max, reduce cardiovascular disease (CVD) risk. One potential mechanism underlying this reduction is greater cardiac autonomic activity and control (ANS). Heart rate and heart rate variability (HRV) are measures of ANS and are used to provide prognostic information. However, the relationships between CRF and HRV has not been yet definitively determined. In most studies, trained individuals have significantly higher standard deviation of RR intervals (SDNN) and root mean square of successive of RR interval differences (rMSSD) compared with insufficiently active people. Data using HRV frequency domain measures, low-frequency (LF) and high-frequency (HF) are less consistent. The aim of this study is to evaluate the associations between VO2max and indices of autonomic modulation in a sample of young adults with a wide range of CRF. METHODS:50 young adults (VO2max 42.21 ± 7.22 and 24.4 ± 3.3 years) completed a graded treadmill test (GXT) to determine CRF. Before the test, participants completed a 6-minutes rest period in the seated position with recording of a 12-lead ECG. Resting HR and HRV outcomes (both time and frequency domains) were assessed at this time. Heart rate recovery (HRR) at 60 and 120 seconds were assessed in the seated position at the end of the 2 minutes of active walking recovery included in the GXT. Separate linear regression models with VO2max as the predictor of interest were run for each of the outcomes, adjusting for age and sex. RESULTS:Resting HR was significantly and negatively (ß = -0.67; p = 0.03) related to VO2max. SDNN, rMSSD, LF and, HF were significantly and positively (ß = 2.28; p < 0.0001, ß = 1.70; p = 0.0003, ß = 0.07; p = 0.0003, and ß = 0.08; p = 0.0009) related to VO2max. HRR60 was not associated with VO2max but HRR120 showed a significant negative (ß = -0.79; p = 0.003) relationship with VO2max. CONCLUSIONS:These results indicate that HRV indicators may provide significant insight on the health of the cardiovascular system as represented by VO2max. Considering the rapid development of wearable monitors, these findings suggest that HRV measured by these devices may be a more easily collected and less expensive index of cardiovascular risk, recognizing that currently and unlike VO2max, established standards for HRV have not yet emerged.