The sympathetic nervous system (SNS) facilitates bodily adjustments needed to accommodate exercise. Electrodermal activity (EDA), a measure of skin conductance mediated by sweat, has been widely used by psychologists as an effective tool to explore SNS-mediated responses to external stimuli. Surprisingly, this technology has been underutilized by exercise physiologists. Because EDA is relatively independent of parasympathetic nervous system regulation, it is a promising surrogate marker for SNS activity during exercise.
PURPOSE: The objectives of this exploratory study were to (1) use EDA to detect the presence and/or magnitude of SNS activity during exercise, and (2) examine the moderating effects of fitness on EDA responses.
METHODS: Eleven healthy, U.S. Navy active-duty men (mean ± SD age, 36.0 ± 6.8 years) participated in a graded exercise test (GXT) to assess maximal oxygen consumption (VO2max) using the Bruce protocol. EDA electrodes were placed on the volar surface of the middle and index phalanges. EDA was recorded at baseline, during GXT, active recovery, and seated recovery. Relative changes for each stage were compared with baseline, and VO2max was used as a marker of fitness. A median split technique was used to establish higher- (n = 5, mean ± SD VO2max, 49.6 ± 1.7 mL·kg-1·min-1) and lower-fit groups (n = 6, mean ± SD VO2max, 43.9 ± 2.3 mL·kg-1·min-1). A 2 (group) x 6 (stage) ANOVA with repeated measures evaluated EDA changes across stages and between higher- and lower-fit groups.
RESULTS: For the total sample, mean changes in EDA from baseline were +38.5%, +47.8%, +54.7%, and +72.2% at Stages 1 through 4, respectively. EDA continued an upward trajectory during active recovery (+87.9%) and then declined during seated recovery (+73.0%) (main effect for stage: F(1.62, 14.53) = 3.86, p = 0.05, η2 = 0.30). Nonsignificant differences between higher- and lower-fit groups were observed for both EDA pattern and magnitude. Specifically, lower-fit EDA responses were elicited earlier and reached a greater level than higher-fit responses, revealing a medium effect size (η2 = 0.06).
CONCLUSIONS: Evidence of dose-dependent increases in SNS activity was detected. The blunted EDA response of more fit individuals may indicate a lower SNS activation requirement compared with less fit individuals during a maximal GXT.