A combination of HRV indices, including Ln rMSSD and the Ln rMSSD:R-R ratio, should be used to accurately monitor cardiac autonomic activity in elite athletes due to the phenomenon of parasympathetic saturation.
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.
Plews et al. (Thu,) studied this question.