Multimodal monitoring of mental fatigue in athletes: Integrating HRV and EEG during training camp sessions

Abstract

This study examined Heart Rate Variability (HRV) and Electroencephalogram (EEG) as non-invasive biosignals for detecting mental fatigue in athletes during a centralized training camp. Eight athletes with normal vision and no history of neurological disorders participated in two experimental sessions (48 and 96 h). RR interval data were recorded using a Polar H10 heart rate sensor, while EEG data were collected with a 32-channel cap based on the 10–20 system. HRV indices in both time (MeanRR, SDNN, RMSSD, pNN50) and frequency domains (LF, HF, LF/HF ratio) were analyzed alongside EEG spectral features (theta and alpha power). Mental fatigue is increasingly recognized as a critical factor affecting athletic performance, cognitive function, recovery capacity, and injury risk during intensive training periods. Despite growing interest in fatigue monitoring, limited research has investigated the combined use of autonomic and neural biomarkers in ecologically valid sports-training environments. The findings demonstrated that at 48 h, athletes exhibited lower RMSSD and pNN50 values accompanied by elevated LF/HF ratios, indicating sympathetic nervous system dominance and increased mental fatigue. EEG recordings simultaneously revealed elevated theta-band activity, confirming reduced alertness and increased cognitive strain. At 96 h, several athletes demonstrated increased RMSSD, SDNN, and pNN50 values together with reduced LF/HF ratios, suggesting partial parasympathetic recovery and autonomic adaptation to prolonged training stress. However, substantial inter-individual variability was observed, indicating that recovery responses differed among athletes. Overall, the results support the use of HRV and EEG as sensitive and complementary biomarkers for monitoring mental fatigue in high-performance sport settings. The integration of autonomic and neural monitoring may provide a practical framework for individualized training management, optimized recovery strategies, prevention of overtraining, and enhancement of athletic performance during intensive training periods.