The interrelation of playing and dancing is central for understanding performance practice in Swedish folk music, as it plays an important role for the metric and rhythmic qualities of spelmansmusik, and playing for dancing is considered a key competence for musicians in this tradition. As part of a research project into performance practice, sound, video and motion capture (MoCap) data were recorded from live performances of three musicians and two dancers in different combinations. In addition, dancing to two recordings by an influential musician and to live and pre-recorded beat clapping was recorded. This paper incorporates measurements and visualizations of performance data in combination with performer participation and interviews. As a starting point for our project, we focus on metric qualities in a historical recording, and on the dance movement patterns to a Swedish polska style with asymmetrical beat patterns. For this paper - as a preliminary investigation into the material - the recordings of one dancer dancing to an isochronous clapped beat, and to a recording by an influential player have been used for comparison of a central movement pattern in dancing. The findings show that asymmetric beat patterns contained in the recording cause wider variation among the movement patterns when compared to the patterns observed to isochronous clapping. Considering the performers reactions towards using MoCap as a tool for viewing and discussing their performances, we propose further investigations by combining scientific, ethnomusicological and artistic research methods into the research of performance practice in folk music.