Non-linear relationship between heart period and root mean square of successive differences during ramp exercise and early recovery

To compare the relationships between heart period and root mean square of successive differences for exercise and recovery, these parameters were obtained in eight subjects during three one-minute successive sub-maximal workloads of cycle exercise and the first three minutes of recovery, using a 25 second sliding window. In most subjects, at recovery, the variables reached values over those at resting condition. Individual semi-log and log-log regressions were estimated and the regression parameters for both stages were compared by paired t-test. All correlations were very strong, higher for the exercise stage, and the regressions were slightly better for the log-log case. The parameters had significant differences between exercise and recovery stages, showing that the relationship between the heart period and the vagal modulation index changed with the subject condition, in this case due to the differences in the response of both variables during the recovery stage