This study examined the effects of four micro-travel keyboards on forearm muscle activity, typing force, typing performance, and self-reported discomfort and difficulty. Twenty participants completed typing tasks on four commercially available devices with different key switch characteristics (dome, scissors, and butterfly) and key travels (0.55, 1.3, and 1.6 mm). The device with short travel (0.55 mm) and a dome type key switch mechanism was associated with higher muscle activities (6-8%,p < 0.01), higher typing force (12%, p < 0.001), slower typing speeds (8%, p < 0.01), and twice as much discomfort (p < 0.05), compared to the three other devices: short travel (0.55 mm) and butterfly switch design and long travel (1.3 and 1.6 mm) with scissor key switches. Participants rated the devices... with larger travels (1.3 and 1.6 mm) with least discomfort (p = 0.015) and difficulty (p < 0.001). When stratified by sex/gender, these observed associations were larger and more significant in the female participants compared to male participants. Because the devices with similar travel but different key switch designs had difference in outcomes and devices with different travel were not different, and the results suggest that key travel alone does not predict typing force or muscle activity.