Table 2. Repeated measures correlations between different heart rate variability and direct current potential variables with competitive performance for four elite international long jump athletes in a 16week period that included the qualification for and competition at the 2016 Olympic Games. 
 r [95% CI] 
p 
LnRMSSD 
0.46 [0.76, 0.01] 
0.03* 
LnRMSSD %CV 
0.41 [0.00, 0.71] 
0.05* 
RR interval 
0.17 [0.58, 0.31] 
0.46 
LnRMSSD:RR 
0.28 [0.65, 0.21] 
0.23 
LnRMSSD7 
0.55 [0.79, 0.17] 
<0.01** 
LnRMSSD:RR7 
0.01 [0.43, 0.42] 
0.97 
DC 
0.09 [0.40, 0.55] 
0.69 
DC7 
0.26 [0.22, 0.64] 
0.26 

LnRMSSD  natural logarithm of the square of the mean sum of the squared differences between RR intervals, LnRMSSD %CV  LnRMSSD coefficient of variation, LnRMSSD:RR  LnRMSSD to RR interval ratio, LnRMSSD7 – LnRMSSD averaged over 7 days, LnRMSSD:RR7  LnRMSSD:RR averaged over 7 days, DC – direct current potential, DC7 – direct current potential averaged over 7 days, r – correlation coefficient; CI – confidence interval, 
