Past research has shown that nonverbal behavior plays an important role in the development and maintenance of a therapeutic relationship. However, the exact nature of specific nonverbal behaviors that help promoting a therapeutic relationship have remained elusive.

Nonverbal synchrony - the coordination of patient's and therapist's body movement - was analyzed in a sample of N = 104 therapy sessions randomly drawn from an archive of routinely recorded ambulatory psychotherapies.

Motion energy analysis (MEA) was used to automatically and objectively quantify nonverbal synchrony in video-recorded therapy sessions. Using a bootstrap approach, it was first ascertained that the phenomenon actually exists: Nonverbal synchrony was compared to the amount of synchrony one would expect to occur by chance. Subsequently, patient's post-session questionnaires and post-therapy outcome assessments were associated with the amount of nonverbal synchrony.

Nonverbal synchrony occurs at a level that is significantly higher than expected by chance. Patient-therapist dyads that showed higher synchrony also reported higher relationship quality and better outcome at the end of therapy.

The coordination of nonverbal behavior is a hitherto neglected facet of the therapeutic relationship. Nonverbal synchrony embodies relevant aspects of both short-term outcome (post-session reports) as well as long-term outcome (post-therapy assessments). Given the fact that the therapeutic relationship is an important change factor, these data indicate that paying more attention to nonverbal aspects of the therapeutic relationship may maintaining the therapeutic relationship and thus increase the chance of patient's improvement.