Postural dynamics and vocal effort: preliminary experimental analysis.

OBJECTIVES One postural characteristic of increased vocal effort is stiffening of the whole body, which in turn induces some postural instability. The study of postural instability can shed some insight into behavior or causes associated with vocal hyperfunction. PATIENTS AND METHODS A posturography platform was used to measure the root mean square of the velocity of variation of the center of pressure (VCOP rms) of control subjects standing upright on the platform. Four conditions were analyzed: (1) standing with eyes open versus eyes closed (n: 9); (2) standing at rest versus holding a 3-kg weight (n: 15); (3) standing while reading a dialogue at normal voice level versus loud voice (n: 17), and (4) standing while reading a dialogue in a calm versus noisy (Lombard effect) ambiance (n: 19). RESULTS Conditions leading to a stiffening of the body (eyes closed and weight holding) were associated with an increased instability assessed by the VCOP rms. In phonatory conditions leading to vocal effort, the mean VCOP rms was significantly increased: in 19 subjects reading a dialogue in a calm ambiance the mean VCOP rms was at 11.19 mm/s, and the VCOP rms raised 16.69 mm/s with surrounding noise at 82 db (Lombard effect). CONCLUSION Increased vocal effort is associated with increased VCOP rms in most subjects studied. The effects of VCOP rms as a postural index allowing noninvasive assessment of the voice in pathology warrants further study.