This may help...

http://link.springer.com/article/10.1007/s00421-014-2907-9

Recently published

The results from longitudinal studies are equivocal, with some showing increased HRV after training but an equal number of studies showing no differences. Further, Supra exercise was shown to worsen the reliability of HRV-spectral indices........"For example, in elite athletes, studies have revealed both increases and decreases in HRV to be associated with negative adaptation. Additionally, signs of positive adaptation, such as increases in cardiorespiratory fitness, have been observed with atypical concomitant decreases in HRV. As such, practical ways by which HRV can be used to monitor training status in elites are yet to be established"

http://www.ncbi.nlm.nih.gov/pubmed/23852425

"In these competitive athletes, short-term interventions resulted in a moderate increase in both resting HR and low frequency/high frequency ratio , and a moderate decrease in maximal HR. Long-term interventions resulted in a small decrease in HR during submaximal and maximal exercise ), without alteration of resting values. The small to moderate amplitude of these alterations limits their clinical usefulness, as expected differences may fall within the day-to-day variability of these markers. Consequently, correct interpretation of HR or HRV fluctuations during the training process requires the comparison with other signs and symptoms of over-reaching to be meaningful"

http://www.ncbi.nlm.nih.gov/pubmed/18308872

"Increases in post-exercise HRV and HRR also occur in response to overreaching, demonstrating that additional measures of training tolerance may be required to determine whether training-induced changes in these parameters are related to positive or negative adaptations"

http://www.ncbi.nlm.nih.gov/pubmed/26888648

"The results from longitudinal studies are equivocal, with some showing increased HRV after training but an equal number of studies showing no differences"

http://www.ncbi.nlm.nih.gov/pubmed/12762827