Powered and passive knee-and-ankle prostheses can restore mobility for individuals with transfemoral amputation (TFA), but their effects on biological joints remain underexplored. Overuse of biological joints with prostheses may lead to chronic pain. This study compared biological joint work during ramp and stair ascent and descent for nine individuals with TFA using the powered prosthesis compared to the passive prosthesis. We hypothesized that the powered prosthesis would reduce positive mechanical work in ascent due to active knee extension and the negative mechanical work in descent due to controlled energy dissipation. In ascent, the powered prosthetic knee generated more positive work (p <​ 0.05), reducing sound-side hip joint work by 29.3 % (CI:​ [1.5 %, 57.1 %];​ p = 0.041) on ramps and 22.8 % (CI:​ [7.2 %, 38.3 %];​ p = 0.019) on stairs. The powered prosthesis reduced biological joint work by 50.6 % (CI:​ [2.7 %, 98.4 %];​ p = 0.041) during swing phase on ramp ascent. In descent, the powered prosthetic ankle absorbed twice the negative work on ramps (CI:​ [164.9 %, 269.9 %];​ p = 0.001) and 2.5 times on stairs (CI:​ [-73.5 %, 372.9 %];​ p = 0.145) by acting as a virtual rotational damper instead of a spring. No significant reductions in biological work were seen in descent tasks, though magnitudes were generally lower. Overall, the powered knee provided biomechanical benefits in ramp and stair ascent, while the powered ankle provided mild benefits in ramp and stair descent. However, the intact joint work remains elevated compared to able-bodied individuals, highlighting the need for further prosthetic improvements.