Correlation Properties Of Heart Rate Variability For Exercise Prescription During Prolonged Running At Different Intensities

Correlation properties of heart rate variability (HRV) captured by the short-term scaling exponent alpha1 of detrended fluctuation analysis (DFA-a1) present a promising monitoring marker of global organismic demand during endurance exercise. PURPOSE: The pilot study aims to assess the potential of DFA-a1 in prescribing and monitoring exercise intensity during continuous prolonged running bouts when transitioning from moderate to heavy, and from heavy to severe exercise domains. METHODS: In thirteen trained endurance athletes (4w, 9 m; maximum heart rate - HRMAX: 196.6 ± 8.7 bpm, peak oxygen consumption - VO2PEAK: 59.3 ± 9.1 ml/kg/min) Running speed (v) at ventilatory thresholds (vVT1, vVT2) as well as at DFA-a1 of 0.75 and 0.5 (vDFAa1-1, vDFAa1-2) were determined during an exhausting ramp test. Afterwards, two 20-min continuous running bouts at vDFAa1-1 and vDFAa1-2 (20-vDFAa1-1, 20-vDFAa1-2) were conducted in randomized order. VO2, HR and DFA-a1 were continuously assessed and blood lactate concentration (BLC) was measured after each bout. RESULTS: External loads of vDFAa1-1 a (10.0 ± 1.5 km/h) and vDFAa1-2 (12.3 ± 1.9 km/h) were slightly lower than those of vVT1 (10.6 ± 1.8 km/h; d = 0.36) and vVT2 (13.1 ± 2.0 km/h; d = 0.44). 20-vDFAa1-1 and 20-DFAa1-2 yielded substantial mean differences in HR (76.4 ± 6.1 vs. 87.0 ± 5.8%HRMAX; d = 1.82), VO2 (62.3 ± 5.3 vs. 78.5 ± 8.4%VO2PEAK; d = 1.75), DFA-a1 (0.86 ± 0.23 vs. 0.60 ± 0.15; d = -1.11) and BLC (1.45 ± 0.58 vs. 3.55 ± 2.35 mmol/l; d = 4.37). In 20-vDFAa1-1 HR increased moderately from 75.4 ± 6.4 to 78.2 ± 6.2% (d = 0.46), while VO2 and DFA-a1 remained rather stable with 62.1 ± 5.4 vs. 62.9 ± 6.0% (d = 0.10) and 0.86 ± 0.30 vs. 0.83 ± 0.18 (d = -0.09). In 20-vDFAa1-2 HR rose from 85.1 ± 6.0 to 89.8 ± 6.1% (d = 0.92), while VO2 (75.4 ± 7.2 to 79.9 ± 9.1%, d = 0.33) and DFA-a1 (0.65 ± 0.21 to 0.57 ± 0.17, d = -0.38) showed moderate changes. CONCLUSIONS: Our data support the notion that DFA-a1 at 0.75 and 0.5 may be used for internal load-based exercise prescription to demarcate the transition from moderate to heavy and heavy to severe intensity. The substantial inter-individual differences in relation to established metabolic and cardiorespiratory markers should be further elucidated in future studies with longer exercise bouts. This may also bear potential for durability assessment of endurance performance.