A morning measurement of resting heart rate has been used to assess fatigue levels in athletes for quite some time now. Generally speaking, higher resting heart rates upon waking are indicative of higher levels of fatigue. Monitoring changes over time is thought to provide a good, objective measure of physical stress. It has been suggested however that heart rate data should be used in conjunction with other metrics of fatigue and performance for meaningful interpretation (Bosquest et al. 2008). Some consider resting heart rate to be too crude of a measure and dismiss its potential usefulness. This simple test is appealing to athletes and coaches however because it requires no cost or special equipment.
A very recent Chinese study investigated the relationship between serum testosterone levels and morning pulse rate in 10 male athletes throughout summer training. Venous blood samples were collected from the athletes on 4 separate occasions throughout the summer training program and serum testosterone levels were measured. In addition, each morning on the day of blood sampling, the athlete’s resting heart rate was recorded after waking. At each of the 4 time points, heart rate and serum testosterone demonstrated a strong correlation (ranging from -0.79 to -0.86). As fatigue accumulated, resting heart rate increased while serum testosterone decreased. As resting heart rate improved to below baseline levels (suggesting increased fitness) testosterone levels increased. It might be worth considering monitoring resting heart rate over the next training cycle to see how it correlates with perceived fatigue and performance markers.
Bosquet, L., Merkari, S., Arvisais, D., & Aubert, A. E. (2008). Is heart rate a convenient tool to monitor over-reaching? A systematic review of the literature. British Journal of Sports Medicine, 42(9), 709-714.
Ma, Z. (2013). Correlation of serum testosterone level and morning pulse in athletes. International Conference on Educational Research and Sports Education