Effects of brief rest periods upon heart rate in multiple baseline studies of heart rate reactivity.

Although there has been some discussion regarding the appropriate length of time necessary for subjects to reach true resting heart rate prior to experimentation, the relevance of conclusions from that discussion for multiple baseline studies of heart rate has not been demonstrated. To investigate this issue, data were collected from 39 males and 33 females following a standard 15-minute adaptation period and then during a series of two-minute experimental phases including stressor tasks and rest periods. Results indicated that, while the group's heart rate during brief rest periods returned to postadaptation levels, there was a substantial subgroup of subjects for whom this was not the case. Implications for the use of multiple baseline procedures in research where heart rate is the dependent variable are discussed.