Since it has been considered that prolonged fatigue has negative influence on sports performance, it would be essential for athletes to continuously monitor day-by-day stress of training. In this study, we examined the relationships between training load and heart rate variability (HRV) indices, salivary cortisol concentration, salivary immunoglobulin A (SIgA) secretion rate, and subjective feeling of fatigue in elite athletes. Eleven Japanese national badminton team players (22.5±3.0 yrs) participated in the study. Data were collected during an 8-day badminton national team training camp. As it was immediately followed by a major international competition, the focus of the training camp was to make the players in good form for the competition. Every morning, beat-to-beat heart rate (HR) was recorded. Spectral analysis was used to calculate spectral power in the high-frequency (HF: 0.15-0.40Hz) band which represents parasympathetic autonomic activity. Saliva samples were collected to measure salivary cortisol concentration and SIgA secretion rate. The subjects were also asked to estimate subjectively perceived fatigue on a visual analogue scale. Training load was quantified by Training Impulse (TRIMPs). As training intensity and duration both decreased in the course of the training camp, TRIMPs in the second half (Day5-8) significantly decreased from that in the first half (Day1-4). In response to the decrease in TRIMPs, mean HR and salivary cortisol concentration significantly decreased in the second half. In contrast, HF significantly increased from the first to the second half. During the training camp, only daily values in HF had significant correlation with daily values in TRIMPs. These results suggest that measuring HRV indices such as HF would be an efficient tool for elite athletes to monitor day-by-day stress of training.

DESCENTE SPORTS SCIENCE Vol.35/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE