Impact of prosodic load on the speed and stability of oral diadochokinesis in healthy young adults.

PURPOSE: Oral diadochokinesis (ODK) is conventionally evaluated by maximum articulatory speed, which may not fully reflect motor control quality. This study examined how intentional rhythmic modulation (prosodic load) affects the speed and stability of ODK tasks in healthy young adults. METHODS: Twenty healthy adults (31.6 ± 4.4 years) performed ODK tasks (/pa/, /ta/, /ka/, and /pataka/) under Normal (maximum speed) and Prosodic (emphasizing the first of every three syllables) conditions. Articulatory rate (syllables/s) and syllable duration coefficient of variation (CoV), used as an index of temporal stability, were calculated. RESULTS: Articulatory rates decreased significantly for all syllables under the prosodic condition compared to the normal condition (P < 0.05). The CoV increased significantly for monosyllables under prosodic load (P < 0.01), indicating reduced stability. However, there was no significant difference in stability for /pataka/. Speed negatively correlated with temporal variability. CONCLUSION: Prosodic control may act as a functional load that suppresses maximum speed and alters rhythmic stability in monosyllabic repetition. Evaluating ODK under prosodic load provides a novel approach to assessing the "quality" of oral motor control, which complements conventional speed measurements.