The use of heart rate variability monitoring for exercise prescription and performance

Abstract

Background: Results from predetermined exercise programs are typically variable, with high, low, and non-responders being reported. These mixed results are likely due to a lack of individualized exercise prescription. Exercise prescription may be enhanced in real-time through the use of individual monitoring techniques such as autonomic nervous activity via heart rate variability (HRV) or hormone responses. The use of HRV provides insight into how an individual responds to an exercise training load, offering practitioners and coaches valuable information about the individual’s adaptations to the overall exercise program. The purpose of this dissertation was to examine the relationship between HRV and other current methods of monitoring individual training responses, the efficacy of HRV to guide high intensity functional training, and whether acute alterations in resting HRV might affect performance. Methods: This dissertation is composed of three different studies. The first study (N = 8) was a 9-week pilot study examining the relationship between HRV and the testosterone-to-cortisol (T:C) ratio during a high-intensity functional training (HIFT) intervention. Second, we investigated the efficacy of daily HRV to guide the prescription of HIFT during a 9-week intervention with recreationally trained individuals (N = 55). Last, we conducted a quasi-experimental study to evaluate differences in cycling performance between normal and abnormal HRV (N = 25). Results: During our pilot study we found a negative relationship between HRV and the T:C ratio with large intra-individual variability. Additionally, we showed that HRV had excellent sensitivity (95%), but poor specificity for detecting meaningful changes in the T:C ratio. Secondly, we observed that the use of daily HRV to guide HIFT training resulted in similar cardiovascular, body composition and fitness improvements outcomes with fewer days training at high intensity than predetermined HIFT. Finally, when an individual’s daily HRV was outside their normal variation, decrements in peak power and peak speed were observed during simulated 40-minute cycling time trials. Conclusion: Our data show that resting HRV may be a clinically utility proxy for indicating hormonal changes during a training intervention. Additionally, we show that HRV is an effective tool for the guidance of HIFT, expanding upon the success of HRV to guide aerobic-based training. Finally, altered daily HRV status may indicate that performance ability is compromised providing support for the notion of decreasing exercise intensity when HRV is outside of normal range. The combined findings from these studies highlight the potential of HRV to enhance exercise prescription through the monitoring of individual training responses by providing practitioners insight into individuals’ internal physiological responses to exercise training and implications for performance.