After 24 weeks , the women in the exercise group showed an increase ( 4.8 0.2 to 5.2 0.2 ) in total power ( LnTP , p < 0.001 ) , low frequency power ( LnLF , p < 0.01 ) , high frequency power ( LnHF , p < 0.001 ) , and the root-mean-square of successive R-R intervals ( rMSSD , p < 0.001 ) .