People in occupations where voice use is central, such as teachers, are more at risk of developing voice disorders. The definition of voice disorders and their possible causes as well as the best methods for preventing them are still being debated. There is also no consensus on the best method of evaluating the voice, although many consider auditory voice quality assessment (where an expert judge listens to a recording of a participant's voice and makes his or her own judgment of its level of abnormality) as a gold standard measure. Voice training is used to prevent voice disorders. Voice training usually consists of a combination of 'direct' and 'indirect' treatment techniques. Direct techniques focus on the underlying physiological changes needed to improve an individual's technique in using the vocal system and may aim to alter vocal fold closure (adduction), respiratory patterns or resonance, pitch or articulatory tension. In practice this means training about how to achieve correct posture, breathing techniques and making various sounds like humming, singing musical scales or yawning. Indirect techniques, on the other hand, concentrate on contributory and maintenance aspects of the voice disorder and may involve relaxation strategies, counselling, explanation of the normal anatomy and physiology of the vocal tract, explanation of the causal factors of voice disorders and voice care and conservation.
We conducted a systematic search of the literature on preventing voice disorders in adults. We then appraised the quality of the studies found and combined their results. We found six studies which met our inclusion criteria. Four were conducted with teachers, one with student teachers and one with telemarketers.
We found no evidence that either direct or indirect voice training nor the two combined are effective in improving vocal functioning when measured using self-reported outcomes and when compared to no intervention.
All the included studies were small and of low methodological quality. Given the extent of the problem and the widespread use of voice training, further research is warranted.