Objectives (1) To quantify acute changes in acoustic parameters of the voices of group fitness instructors (GFIs) before and after exercise instruction. (2) To determine whether these changes are discernible perceptually by the instructor. Study Design This is a pilot prospective cohort study. Methods Participants were six female GFIs, based in Brisbane, Australia. Participants performed a series of vocal tasks before and after instruction of a 60-minute exercise class. Data were obtained pertaining to fundamental frequency (pitch), intensity (volume), jitter, shimmer, harmonic-to-noise ratio (HNR), maximum duration of sustained phonation (MDSP), and pitch range. Additionally, self-ratings of voice quality were obtained before and after instruction. Data were analyzed using the Wilcoxon signed rank test. Results Significant increases (P ≤ 0.05) were found in fundamental frequency and intensity after instruction. No significant changes in jitter, shimmer, HNR, or MDSP were found before and after instruction. For the group, no significant change in self-ratings of voice quality occurred before and after instruction. Conclusions Statistically significant changes in pitch and volume were found on acoustic analysis. However, these subtle changes remained within the limits of what is considered normal and representative of the participant's age and gender. Further research into the effects of exercise instruction on the voice is needed.