Day-to-Day Heart-Rate Variability Recordings in World-Champion Rowers: Appreciating Unique Athlete Characteristics

Purpose: Heart-rate variability (HRV) is a popular tool for monitoring autonomic nervous system status and training adaptation in athletes. It is believed that increases in HRV indicate effective training adaptation, but these are not always apparent in elite athletes. Methods: Resting HRV was recorded in 4 elite rowers (rowers A, B, C, and D) over the 7-wk period before their success at the 2015 World Rowing Championships. The natural logarithm of the square root of the mean sum of the squared differences (Ln rMSSD) between R-R intervals, Ln rMSSD:R-R ratio trends, and the Ln-rMSSD-to-R-R-interval relationship were assessed for each championship-winning rower. Results: The time course of change in Ln rMSSD was athlete-dependent, with stagnation and decreases apparent. However, there were consistent substantial reductions in the Ln rMSSD:R-R ratio: rower A, baseline toward wk 5 (-2.35 +/- 1.94); rower B, baseline to wk 4 and 5 (-0.41 +/- 0.48 and -0.64 +/- 0.65, respectively); rower C, baseline to wk 4 (-0.58 +/- 0.66); and rower D, baseline to wk 4, 5, and 6 (-1.15 +/- 0.91, -0.81 +/- 0.74, and -1.43 +/- 0.69, respectively). Conclusion: Reductions in Ln rMSSD concurrent with reductions in the Ln rMSSD:R-R ratio are indicative of parasympathetic saturation. Consequently, 3 of 4 rowers displayed substantial increases in parasympathetic activity despite having decreases in Ln rMSSD. These results confirm that a combination of indices should be used to monitor cardiac autonomic activity.