The ratio of heart rate to heart rate variability reflects sympathetic activity during incremental cycling exercise

Figures & data

Figure 1. Representative data during an incremental exercise test in a female participant. The white box indicates the rest period. The gray box indicates the warm-up period, during which the participant cycled at 10 W. The black box indicates the period of 10-W incremental increases in exercise workload every minute until exhaustion. The black arrow indicates the workload at the LT. HF, high-frequency component; HR, heart rate; LF, low-frequency component; W-up, warm-up.

Table 1. Physiological parameters and heart rate variability components in each stage during the incremental exercise test.

Outcome	Rest	Lactate threshold (LT)	Ventilatory threshold (VT)	Exhaustion
Exercise load (watts)	0 ± 0	94 ± 21	88 ± 12	217 ± 37
⩒O2 (ml/kg/min)	4.5 ± 0.7	21.2 ± 3.6^a	20.3 ± 2.5^a	42.8 ± 4.8^abc
Blood lactate (mmol/L)*	1.1 ± 0.2	1.4 ± 0.3^a	1.4 ± 0.4^a	8.1 ± 1.7^abc
Respiratory rate (breaths/min)	16 ± 3	27 ± 6^a	26 ± 4^a	50 ± 8^abc
Heart rate (beats/min)	76 ± 12	117 ± 16^a	114 ± 15^a	183 ± 9^abc
R-R interval (ms)	811 ± 123	521 ± 72^a	536 ± 75^a	328 ± 16^abc
LF (ms^2)	1455 ± 613	91 ± 140^a	107 ± 134^a	3 ± 6^abc
HF (ms^2)	767 ± 900	48 ± 67^a	67 ± 108^a	10 ± 24^ac
Heart rate / LF	0.1 ± 0.0	5.9 ± 7.8^a	2.8 ± 2.5^a	1628.5 ± 2178.0^abc
LF / HF	3.4 ± 2.9	2.2 ± 1.2	2.6 ± 2.0	0.3 ± 0.1^abc

Notes: Values are mean  ±  SD (n = 15). Note that the values of blood lactate at VT period (n = 14) and HRV components at exhaustion period (LF, HF, Heart rate/LF, LF/HF, n = 14) were missing. ⩒O₂: oxygen uptake, LT: lactate threshold, VT: ventilatory threshold, LF: low-frequency component, HF: high-frequency component.

* The blood lactate value at LT and VT were adopted according to the value closest to each threshold within  ±10% of the exercise load corresponding to each threshold. The blood lactate at exhaustion was the value 3 min after the participant finished the exercise test.

^a p < 0.05 vs. Rest.

^b p < 0.05 vs. LT.

^c p < 0.05 vs. VT.

Figure 2. Changes in HRV components and physiological parameters before and after reaching the LT. Data are shown the mean ± SD. A, HRV components (Heart rate/LF, n = 14–15; LF/HF, n = 14–15) and HR (n = 15). B, Blood parameters (adrenaline, n = 10–12; noradrenaline, n = 10–12; blood lactate, n = 14–15). C, Respiratory gas parameters (⩒O₂, n = 15; ⩒CO₂, n = 15; RQ, n = 15). The relative intensity of workload with respect to the LT is shown in the horizontal axis. The obtained values were averaged as percentage ranges. *p < 0.05 at rest vs. each relative intensity. HF, high-frequency component; HR, heart rate; LF, low-frequency component; LT, lactate threshold; RQ, respiratory quotient; ⩒O₂, oxygen uptake; ⩒CO₂, carbon dioxide production.

Figure 3. Correlations between HRV components and physiological parameters. All data are the values from at rest to until the blood lactate reached 4 mmol/L. All data are presented as logarithms (log). (A) The correlation between Heart rate/LF and blood, respiratory gas parameters. (B) The correlation between LF/HF and blood, respiratory gas parameters. HF, high-frequency component; HR, heart rate; LF, low-frequency component; RQ, respiratory quotient; ⩒O₂, oxygen uptake; ⩒CO₂, carbon dioxide production.