Excel dataset of the study variables.

Emotion regulation (ER) is a key competence in adolescence that is related to multiple psychological outcomes, including adaptive functioning and psychopathological symptoms. The development of ER skills is closely associated with a child’s family relational context. Nevertheless, few studies have investigated the physiological ER of adolescents during family interactions that go beyond the mother–adolescent dyad. Thus, little is understood regarding which features of communication in the mother–father–adolescent triad (e.g., warmth of affective exchanges) are relevant to adolescents’ physiological ER (as indexed by heart rate variability; HRV). The objective of this study was to explore the associations between the observed quality of triadic family interactions and adolescents’ physiological ER. This study investigated 77 mother–father–adolescent triads from the general population during a semi-standardized observational situation, the Lausanne Trilogue Play – Conflict Discussion Task (LTP–CDT). We assessed the quality of family interactions using an observational coding instrument, the Family Conflict and Alliance Assessment Scales – with adolescents (FCAAS), which includes scales on communicational aspects such as turn-taking, conflict resolution, affective climate, mentalization, and scales related to indicators of the coparenting relationship (e.g., coparenting support). We measured adolescents’ HRV before (baseline), during (reactivity), and after (recovery) the LTP–CDT by computing the root mean square of successive differences (RMSSD) between heartbeats as indices of adolescents’ physiological ER in each part of the procedure. Regression analyses showed significant associations between coparenting-related indicators (e.g., coparenting support) during mother–father–adolescent conflictual interactions and various measures of adolescents’ physiological ER capacities. These results highlight that family-level processes such as the coparenting relationship may be significant relational contexts for the socioemotional development of adolescents. The discussion encompasses research perspectives (e.g., extending our investigations to family triads involving a clinically referred member) and potential clinical implications (e.g., incorporating the coparenting unit into psychotherapy with adolescents).