RESUMO
It has been shown that the time constant of heart rate decline for the first 30 sec (T<SUB>30</SUB>) after exercise, at an intensity lower than the ventilatory threshold (VT), can serve as a specific index to assess post-exercise vagal reactivation. The purpose of this study was to validate the use of a simpler alternative index, i. e. %Δ HR<SUB>30</SUB> (the ratio of heart rate decrement for the first 30 sec after exercise) for the evaluation of parasympathetic nervous reactivation, and to examine whether it would be a useful index in the conditioning of athletes. Eighteen college students performed 4 minutes cycle ergometer exercise routines at intensities of 40%, 80%, and 120% VT to compare the %Δ HR<SUB>30</SUB> and the T<SUB>30</SUB>. In addition, the %Δ HR<SUB>30</SUB> was obtained by a field test (4 minutes jogging) in 15 college middle and long distance runners, every morning during summer camp training to assess the state of athletic conditioning. The %Δ HR<SUB>30</SUB> at 80% VT was similar to the value at 40% VT, but significantly different from the value at 120% VT, as was the T<SUB>30</SUB> at 80% VT.<BR>The %Δ HR<SUB>30</SUB> significantly correlated with the T<SUB>30</SUB> and VO<SUB>2</SUB>max. During the camp, the %Δ HR<SUB>30</SUB> was higher on mornings following light training days than on mornings following hard training days. These results suggest that the %Δ HR<SUB>30</SUB>, at an exercise intensity lower than the VT, could be a simple and useful index to evaluate post-exercise parasympathetic nervous reactivation in the conditioning of athletes.