Loading and gait symmetry during level and stair walking in asymptomatic subjects with knee osteoarthritis: importance of quadriceps femoris in reducing impact force during heel strike? - Liikavainio,T.; Isolehto,J.; Helminen,HJ.; Perttunen,J.; Lepola,V.; Kiviranta,I.; Arokoski,JP.; Komi,PV. (Knee, 2007)