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INTRODUCTION Mechanical ventilation (MV) induced diaphragmatic atrophy can contribute to weaning difficulties. A temporary transvenous diaphragm neurostimulation (TTDN) device that elicits diaphragm contractions has previously been shown to mitigate atrophy during MV in a preclinical model; however, its effects on different myofiber types remain unknown. It is important to examine these effects, as each myofiber type plays a role in the range of diaphragmatic movements to ensure successful liberation from MV. METHODS Eighteen pigs were assigned to one of three ventilation conditions for 50 hours: MV-Only, and TTDN contracting the diaphragm every other breath or every breath synchronously with MV (TTDN50%+MV and TTDN100%+MV, respectively). Six pigs were assigned to a never-ventilated, never-paced (NV-NP) group. Diaphragm biopsies were fiber-typed and myofiber cross-sectional areas were measured and normalized to subject weight. RESULTS There were effect differences based on TTDN exposure. The TTDN100%+MV group showed less atrophy in Type 2A and 2X myofibers than the TTDN50%+MV group, relative to the NV-NP group. The TTDN50%+MV animals showed less MV-induced atrophy in Type 1 myofibers than TTDN100%+MV animals. Additionally, there were no significant differences in proportions of myofiber types between each condition. CONCLUSION TTDN applied synchronously with MV for 50 hours mitigates MV-induced atrophy in all myofiber types, with no evidence of stimulation-induced myofiber-type shift. At this stimulation profile, enhanced protection for Type 1 myofibers and Type 2 myofibers was seen when diaphragm contractions occurred every other breath and every breath, respectively.