During social interactions, people tend to coordinate their movements and become synchronized. People, for example, spontaneously synchronize their footsteps when walking side-by-side, orchestrate the swing of their postures when conversing, and fall into synchronous patterns when tapping together. The spontaneous capacity for interpersonal synchrony apparently has its roots in early childhood. Mothers’ and their infants’ rhythmic cycles naturally synchronize with each other. For example, mother and infant’s heart rates become coordinated during free play. The early rise of interpersonal motor coordination suggests that it facilitates social interactions with caregivers by satisfying the need for connection and physical safety.

Simple motor synchrony may inspire a sense of unity even between previously unacquainted interactional partners and have vast social consequences, such as heightened feelings of connectedness as well as increased cooperation and compassion. Within the context of romantic relationships, synchrony has long been considered as an indication of successful relationships. Surprisingly, however, the influence of synchrony on deeper aspects of experienced intimacy, such as those typical of close relationships (e.g., empathy, perceived responsiveness) has not been experimentally established yet.

Research published recently in the Journal of Social and Personal Relationships has examined whether interpersonal motor synchrony, the temporal alignment of simple motor periodic behaviors between interactional partners, instills perceptions of intimacy among both strangers and romantic partners. In four studies, my colleagues and I wished to demonstrate the intimacy-promoting function of synchrony in relationship initiation and development. In such affective contexts, the need to connect is especially salient and thus might encourage both new acquaintances and long-term intimates to rely on non-verbal cues that signal contact readiness.

In Study 1, dyads of same-sex unacquainted individuals were pedaling, facing each other, on two stationary bicycles with a shared front wheel, while one of the dyad members (“the discloser”) was disclosing either a neutral or a positive affective event (e.g., a work promotion). The other member (“the responder”) was asked to listen attentively to the disclosure. Spontaneous motor synchrony was measured by the synchrony between dyad members’ pedaling velocities. Following this procedure, both participants rated how close they felt to each other. The disclosing participants rated their perception of the responders’ responsiveness, whereas the responding participants rated how empathetic they felt toward the disclosers. Synchrony was associated with the deeper aspects of intimacy during an affective interaction, but not during a neutral interaction.

In Study 2, we sought to establish a causal link between synchrony and intimacy during an affective interaction between same-sex strangers. To do so, we experimentally manipulated the synchrony between dyad members while they were pedaling on two stationary bicycles. Specifically, one member of each dyad disclosed a recent positive event, and the other member listened to the story attentively, while riding bicycles either synchronously (in the in-sync condition) or non-synchronously (in the out-of-sync condition). Following the disclosure, the participants rated their perceptions of rapport, partner responsiveness (disclosers), and empathy (responders). We found that motor synchrony enhanced self-reported rapport, empathy, and perceptions of responsiveness between previously unacquainted individuals.

In the next two studies, we sought to investigate whether the effect of synchrony would enhance an already intimate relationship and generalize to the sexual domain by examining the effect of motor synchrony on intimacy within heterosexual romantic relationships. In Study 3, romantically involved participants heard the sound of either coordinated or uncoordinated footfalls and were asked to imagine themselves walking side-by-side with their partner. Following this imagery task, participants rated how intimate they felt with their partner.

The findings showed that imagined synchronized interactions with one’s partner led to higher levels of felt intimacy with this partner as compared with out-of-sync interactions. Hence, not only can synchrony affect the development of closeness between strangers, but it may also boost levels of intimacy in ongoing romantic relationships. Within this context, synchrony can signify unity between partners, thereby generating an atmosphere ripe for reciprocal exchanges of intimacy that may further intensify the emotional bond between them.

Study 4 set out to clarify whether the difference in felt intimacy between in-sync and out-of-sync conditions reflects the positive influence of synchrony or the negative influence of a lack of synchrony. For this purpose, participants were assigned to one of three synchrony conditions: breathing in-sync with their partner, breathing out-of-sync with their partner, and breathing in-sync with a koala. Following the breathing interaction, participants rated how intimate they felt with their partner and described a sexual fantasy narratively. Independent judges coded these narratives for closeness and sexual desire themes. The results indicated that participants experienced higher levels of rapport with their partner in the in-sync condition than in the other conditions. In addition, perceptions of synchrony with one’s partner were associated with perceptions of closeness, which in turn, predicted heightened sexual desire for one’s partner.

Overall, in line with previous studies, we found that enacted synchronous behavior (real or imaginary) with a stranger or with a romantic partner instilled consistent feelings of closeness across four experimental studies. We extended previous findings by showing that in addition to closeness, enacted or perceived synchrony is associated with profound interpersonal feelings indicative of intimacy, including empathy and perceived responsiveness (Studies 1 and 2), actual levels of intimacy in relationships (Study 3), and sexual desire for a partner (Study 4).

Our findings suggest that synchrony may serve as a basic intimacy-promoting strategy needed for both relationship initiation and development. Previous research has underscored the importance of participating in novel and arousing activities to maintaining passionate and satisfying relationships. Our research suggests that even non-verbal displays of synchrony during ordinary activities in everyday lives can deepen the experience of closeness and sexual desire between partners.