The main focus of the analysis is the musical accompaniment in traditional string bands in the village of Telgárt (Horehronie region in central Slovakia) with a particular focus on its rhythmic structure. In traditional bands in Slovakia, a specific rhythmic pattern, or motif with a relatively stable timing and dynamic structure is its basic structural component. By its repetition, players create a sense of periodic pulsation in the dance music. Several particular types of these motifs have developed in relation to the types or historic layers of traditional dance. However, in many bands, they are interpreted in slightly different ways by individual accompanying players. The main aim of the analysis was to identify all individual rhythmic variants of all basic types of rhythmic accompaniment played by five viola players within three generations of Romani musicians. In the process of analysis, we apply the approach of music psychologist and ethnomusicologist J. Baily − rhythmic motifs are analyzed with an emphasis on movement patterns underlying their musical interpretation. Instead of European notation, we use a system of alphanumeric codes, which communicates their basic rhythmic and movement aspects: constitutive rhythmical units, bowing technique, accent placement (using bow pressure), and the relative length of rhythmical units. A total of 47 variants of 5 basic types as well as new patterns, were identified in 18 audio and audio-visual source materials recorded between 1961 and 2018. The study is the first part of a series of two related papers. After the process of identification and systematization of rhythmic variants in the present study, a second paper will put all of the identified variants into a cultural and musical context and interpreted in terms of their relationship to dance songs, dance types, and the interplay of players in the ensemble and intergenerational differences in playing styles.