Optimization of maximal rate of heart rate increase assessment in runners

Purpose: Correlations between fatigue-induced changes in exercise performance and maximal rate of heart rate (HR) increase (rHRI) may be affected by exercise intensity during assessment. This study evaluated the sensitivity of rHRI for tracking performance when assessed at varying exercise intensities. Method: Performance (time to complete a 5-km treadmill time-trial [5TTT]) and rHRI were assessed in 15 male runners following 1 week of light training, 2 weeks of heavy training (HT), and a 10-day taper (T). Maximal rate of HR increase (measured in bpm·s−¹) was the first derivative maximum of a sigmoidal curve fit to HR data recorded during 5 min of running at 8 km·h⁻¹ (rHRI⁸–¹³ᵏᵐ·ʰ−¹), and during subsequent transition to 13 km·h−¹ (rHRI⁸–¹³ᵏᵐ·ʰ−¹) for a further 5 min. Results: Time to complete a 5-km treadmill time-trial was likely slower following HT (effect size ± 90% confidence interval = 0.16 ± 0.06), and almost certainly faster following T (–0.34 ± 0.08). Maximal rate of HR increase during 5 min of running at 8 km·h−¹ and rHRI⁸–¹³ᵏᵐ·ʰ−¹ were unchanged following HT and likely increased following T (0.77 ± 0.45 and 0.66 ± 0.62, respectively). A moderate within-individual correlation was found between 5TTT and rHRI⁸–¹³ᵏᵐ·ʰ−¹ (r value ± 90% confidence interval = –.35 ± .32). However, in a subgroup of athletes (n = 7) who were almost certainly slower to complete the 5TTT (4.22 ± 0.88), larger correlations were found between the 5TTT and rHRI⁸–¹³ᵏᵐ·ʰ−¹ (r = –.84 ± .22) and rHRI⁸–¹³ᵏᵐ·ʰ−¹ (r = –.52 ± .41). Steady-state HR during rHRI assessment in this group was very likely greater than in the faster subgroup (≥ 1.34 ± 0.86). Conclusions: The 5TTT performance was tracked by both rHRI⁸–¹³ᵏᵐ·ʰ−¹ and rHRI⁸–¹³ᵏᵐ·ʰ−¹. Correlations between rHRI and performance were stronger in a subgroup of athletes who exhibited a slower 5TTT. Individualized workloads during rHRI assessment may be required to account for varying levels of physical conditioning. Refereed/Peer-reviewed