“…For these dynamics, the most relevant parameter is the Hurst exponent, which quantifies the time scaling of the stochastic process or time series: by definition, if we note H the Hurst exponent of a stochastic process S t , an increment of duration d, S t+d − S t , has the same probability distribution as d H (S t+1 − S t ), for all time t. The Hurst exponent can be estimated by several methods. For the analysis of the HRV, it has been estimated by the method of absolute moments [9], rescaled range analysis (R/S) [31,34] and detrended fluctuation analysis (DFA), in which the HRV signal is detrended by a piecewise linear trend [41,40,13,52,48] or by a moving average [5]. Among these three techniques, our preference goes to the method of absolute moments [39,18] because it does not need a dataset as big as for computing R/S analysis or DFA, which are based on regressions on many subsamples.…”