The Sing-a-Song Stress Test (SSST) was recently developed as an alternative to the Trier Social Stress Test (TSST) to investigate autonomic nervous system responses to social-evaluative stress. In the SSST, participants are suddenly cued to sing a song in the presence of confederates. However, the SSST is still quite long (~15 min) and the requirement for confederates makes it labor-intensive. The current study tested whether a shorter (~6.5 min), single-experimenter, version of the SSST can still reliably elicit subjective and physiological stress reactivity. Our sample consisted of 87 healthy young adult participants (age range: 18–35 years). During the short SSST and a speeded reaction time task, in which aversive loud tones were to be avoided (TA), we measured heart period (HP), sympathetic nervous system (SNS) activity using pre-ejection-period (PEP), skin conductance level (SCL), and non-specific skin conductance responses (ns.SCR), and parasympathetic nervous system (PNS) activity using respiratory-sinus-arrhythmia (RSA) and the root-mean-square of successive differences (RMSSD). The short SSST induced significant decreases in positive affect and increases in negative affect. MANOVAs on the clusters of SNS and PNS variables showed that the short SSST elicited significant HP (−118.46 ms), PEP (−7.76 ms), SCL (+4.85 μS), ns.SCR (+8.42 peaks/min) and RMSSD (−14.67) reactivity. Affective, SNS, and PNS reactivity to the new SSST social-evaluative stress task were of comparable magnitude to that evoked by the TA mental stressor. We conclude that the short SSST is a valid and cost-effective task for large scaled studies to induce social-evaluative stress to a sufficient degree to evoke measurable changes in PNS and SNS activity and affective state.

The cross-stressor adaptation hypothesis—which posits that adjustment to physical stress as a result of regular physical activity and its effects on fitness crosses over to psychological stress reactivity—has been around for over four decades. However, the literature has been plagued by heterogeneities preventing definitive conclusions. We address these heterogeneity issues in a combined laboratory and daily life study of 116 young adults (M = 22.48 SD = 3.56, 57.76% female). The exposure, i.e., the potential driver of adaptation, was defined in three ways. First, a submaximal test was performed to obtain aerobic fitness measured as the VO2max (kg/ml/min). Second, leisure time exercise behavior, and third, overall moderate-to-vigorous physical activity (MVPA), were obtained from a structured interview. Outcomes were autonomic nervous system (ANS) reactivity and affective responsiveness to stressors. ANS activity was measured continuously and expressed as inter-beat-interval (IBI), pre-ejection-period (PEP), respiratory sinus arrythmia (RSA), and non-specific Skin Conductance Responses (ns.SCR). Negative and positive affect were recorded after each experimental condition in the laboratory and hourly in daily life with a nine-item digital questionnaire. Linear regressions were performed between the three exposure measures as predictors and the various laboratory and daily life stress measurements as outcomes. Our results support the resting heart rate reducing effect of aerobic fitness and total MVPA in both the laboratory and daily life. We did not find evidence for the cross-stressor adaptation hypothesis, irrespective of ANS or affective outcome measure or whether the exposure was defined as exercise/MVPA or aerobic fitness.

Respiratory sinus arrhythmia (RSA) is the heart period variability observed in synchrony with respiration. RSA amplitude is widely used in psychophysiological research to non-invasively index cardiac vagal activity. However, RSA measures are significantly affected by respiratory behavior, even in the absence of changes in cardiac vagal activity. Fifty-to-sixty percent of the variation in RSA can be attributed to respiration rate and tidal volume. This poses a notable challenge for ambulatory RSA measurement where respiratory behavior cannot be experimentally controlled and can show substantial variation. This pre-registered two-day ambulatory study (https://osf.io/57es4) compared four approaches to control for respiratory influences on RSA, to make an empirical recommendation on how to best capture cardiac vagal activity in daily life. We evaluated how well the RSA metric of each approach predicted (1) Minute-to-minute heart period, assumed to be predominantly governed by cardiac vagal activity, and (2) Perceived stress, positive affect, negative affect, and safety—states expected to elicit fluctuations in cardiac vagal activity— at smartphone prompts. The tidal volume-normalized RSA approach was optimal, explaining 1.47 times as much within-individual variance in heart period as that explained by uncontrolled-RSA. The need to use respiratory-controlled RSA was further highlighted by results on safety. Perceived safety was associated with uncontrolled-RSA (p = .033) but not with any of the controlled-RSA metrics. This relationship was driven by higher respiration rate co-occurring with lower safety. We recommend using tidal volume-normalized RSA in ambulatory research to avoid reporting spurious within-individual correlations between psychological states and cardiac vagal activity.