A global inversion procedure from the acoustic signal to motor commands is presented here based on a postural target invariance hypothesis. Using a model of vowel production, dynamic motor commands were inferred for a vowel sequence pronounced under different levels of emphasis stress and rate. The results enable to assign a prosodic role to the dynamic parameters of the model and thus to discriminate between slow vs fast or stressed vs unstressed utterances. Reliability of the results was assessed by computing the sensitivity of the model around the inferred motor commands and running perceptual tests on the synthetic stimuli generated from these values.