During stair ambulation, what range of knee joint load is transmitted through the patellofemoral joint (PFJ) relative to body weight?

• A. 2.5-3.5x body weight
• B. 1-2x body weight
• C. 3.5-4.5x body weight
• D. 4-6x body weight

Answer: (A)

During stair ambulation, the patellofemoral joint is subjected to substantial compressive forces because the quadriceps pull on the patella as the knee flexes to lift the body. This combination of knee flexion angle and strong quadriceps activation increases the PFJ reaction force to several times body weight. In typical stair ascent, that load is about 2.5 to 3.5 times body weight. This range reflects the higher demands of stairs compared with level walking, where loads are closer to 1–2 times body weight, while still being lower than extreme squats or jumping.