After multivariable adjustment , greater total leisure-time activity , walking distance , and walking pace were each prospectively associated with specific , more favorable HRV indices , including higher 24-hour standard deviation of all normal-to-normal intervals ( Ptrend = 0.009 , 0.02 , 0.06 , respectively ) and ultralow-frequency power ( Ptrend = 0.02 , 0.008 , 0.16 , respectively ) .