Endurance training guided individually by daily heart rate variability measurements

Purpose of this study was to test utility of heart rate variability (HRV) in daily endurance exercise prescriptions. Twenty-six healthy, moderately fit males were randomized into predefined training group (TRA, n = 8), HRV-guided training group (HRV, n = 9), and control group (n = 9). Four-week training period consisted of running sessions lasting 40 min each at either low- or high-intensity level. TRA group trained on 6 days a week, with two sessions at low and four at high intensity. Individual training program for HRV group was based on individual changes in high-frequency R–R interval oscillations measured every morning. Increase or no change in HRV resulted in high-intensity training on that day. If there was significant decrease in HRV (below reference value [10-day mean-SD] or decreasing trend for 2 days), low-intensity training or rest was prescribed. Peak oxygen consumption (VO_2peak) and maximal running velocity (Load_max) were measured in maximal treadmill test before and after the training. In TRA group, Load_max increased from 15.1 ± 1.3 to 15.7 ± 1.2 km h⁻¹ (P = 0.004), whereas VO_2peak did not change significantly (54 ± 4 pre and 55 ± 3 ml kg⁻¹ min⁻¹ post, P = 0.224). In HRV group, significant increases were observed in both Load_max (from 15.5 ± 1.0 to 16.4 ± 1.0 km h⁻¹, P < 0.001) and VO_2peak (from 56 ± 4 to 60 ± 5 ml kg⁻¹ min⁻¹, P = 0.002). The change in Load_max was significantly greater in HRV group compared to TRA group (0.5 ± 0.4 vs. 0.9 ± 0.2 km h⁻¹, P = 0.048, adjusted for baseline values). No significant differences were observed in the changes of VO_2peak between the groups. We concluded that cardiorespiratory fitness can be improved effectively by using HRV for daily training prescription.