The only commercially available ankle-foot prosthesis with powered propulsion lacks ruggedization and other capabilities for service members seeking to return to duty and/or other physically demanding activities. Here, we evaluated a ruggedized powered ankle-foot prosthesis with electromyographic control ("Warrior Ankle"; WA) in an experienced male user of the predicate (Empower) prosthesis. The participant (age = 56 years, mass = 86.8 kg, stature = 173 cm) completed a 650 m simulated hike with varying terrain at a fixed, self-selected speed in the WA and predicate prosthesis, with and without a 22.8 kg weighted vest ("loaded" and "unloaded," respectively). Peak dorsiflexion and plantarflexion angles were extracted from each gait cycle throughout the simulated hike (∼500 prosthetic-side steps). The participant walked faster with the WA (1.15 m/s) compared to predicate (0.80 m/s) prosthesis. On the prosthetic side, peak dorsiflexion angles were larger for the WA (loaded: 27.9°; unloaded: 26.9°) compared to the predicate (loaded: 19.4°; unloaded: 21.3°); peak plantarflexion angles were similar between prostheses and loading conditions [WA (loaded: 15.5°; unloaded: 14.9°), predicate (loaded: 16.9°; unloaded: 14.8°). The WA better accommodated the varying terrain profile, evidenced by greater peak dorsiflexion angles, as well as dorsiflexion and plantarflexion angles that more closely matched or exceeded those of the innate ankle [dorsiflexion (WA: 31.6°, predicate: 27.5°); plantarflexion (WA: 20.7°, predicate: 20.5°)]. Furthermore, the WA facilitated a faster walking speed, suggesting a greater functional capacity with the WA prosthesis. Although further design enhancements are needed, this case study demonstrated feasibility of a proof-of-concept, ruggedized powered ankle-foot prosthesis with electromyographic control.