modestly significantp = 0.01
However, multivariable linear regression involving both age and the intra-individual heart rate changes as independent variables showed that age was the main determinant of nHF changes (p < 0.001 in all comparisons) with only modestly significant influence of heart rate changes in test 1 (p = 0.01 and p = 0.03 for females and males, respectively) and with no significant influence of heart rate changes in test 2. 4 Discussion The study provides two potentially unexpected observations.