Estimation of Training Fatigue and Overtraining: Examination of a New Method Using Electrocardiogram Frequency Analysis

Abstract

The autonomic nervous component obtained from heart rate variability can potentially be used to estimate overtraining. However, no method has been established to estimate temporary training fatigue using heart rate variability. We examined whether the autonomic nervous component response for exercise load can estimate temporary training fatigue. Five participants （age: 21.2 ± 0.8 yrs; height: 174.6 ± 2.5 cm; weight: 62.5 ± 6.0 kg; maximal oxygen uptake [V･O₂max]: 44.5 ± 5.8 ml/kg/min） completed sprint training for 5 days at 70% of each participant’s maximum sprint speed. Heart rate variability was measured during exercise load at the lactate threshold for 5 min using an electrocardiogram before and after training for 5 days. Heart rate variability was automatically translated into the autonomic nervous component using automatic frequency analysis （low-frequency power [LF], high-frequency power [HF], LF/HF）．Feelings of fatigue were measured using the Visual Analogue Scale （VAS） after exercise load before and after sprint training for 5 days. Feelings of fatigue after exercise load increased after training compared with that before training （p<0.05）．Moreover, feeling fatigued was correlated with a decreased LF component during exercise load （reflecting sympathetic nervous and parasympathetic nervous activities; r=-0.988, p<0.05）．HF （parasympathetic nervous activity） and LF/HF （sympathetic nervous activity） during exercise load were not correlated with feeling fatigued after exercise load （HF: r=-0.082, p=0.895; LF/HF: r=-0.424, p=0.477）．The autonomic nervous component （LF） response for exercise load can potentially be used to estimate temporary training fatigue.