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OBJECTIVES: The intensity of muscle activity immediately following intramuscular botulinum toxin injection may affect the clinical efficacy of the injection. We tested this effect in patients who underwent botulinum toxin injections for adductor spasmodic dysphonia. METHODS: Patients were studied over 3 to 5 injection cycles. Cycle 1 was the baseline control; cycle 2 was randomized between a 1-hour reading aloud task ("exercise") and a 24-hour period of complete voice rest. For cycle 3, the patient completed the task not performed in cycle 2. Patients who were willing to continue for cycles 4 and 5 repeated the experiment at one half the injection dosage. Efficacy was determined with a battery of voice recordings and clinical outcomes instruments administered via telephone at 2- to 4-week intervals. The primary outcome measure was the result of the Voice-Related Quality of Life (VRQOL) instrument. RESULTS: Nine patients (8 women, 1 man) with a mean age of 60.8 years (range, 42 to 76 years) completed at least 3 injection cycles. The VRQOL results were significantly higher for cycles that followed the exercise task. The patients reported subjectively that these were some of the best injection cycles they had ever experienced. Some achieved equivalent results with the half-dose injection plus exercise. The VRQOL results after voice rest cycles were not significantly different from the patients' baseline cycles. CONCLUSIONS: These results support the conclusion that a period of intense vocalization immediately following laryngeal botulinum toxin injections improves the efficacy of the injection. Possible mechanisms are proposed.