1. Knee osteoarthritis (OA) causes pain, reduced function and quality of life and is associated with reduced quadriceps muscle strength. Quadriceps strengthening is recommended as treatment of these negative outcomes based on the widely accepted hypothesized mechanism that increased quadriceps strength increases quadriceps force and negative muscle work in locomotion, supposedly reducing knee joint loading and mediating clinically beneficial effects. We propose this mechanism to be flawed in that increased muscle force would increase joint loading and negative muscle work does not reduce joint loads but total body mechanical energy. The purpose of this study was to assess the effect of quadriceps strengthening on quadriceps muscle force, power and work and knee joint forces in stair ascent and descent. These tasks are quadriceps-demanding and include both concentric and eccentric contractions. Quadriceps Strengthening Does Not Change Quadriceps and Knee Biomechanics During Stair Ascent and Descent in Adults With Knee Osteoarthritis Paul DeVita 1, Josh Leonardis 1, Marius Henriksen 2, Cecilie Bartholdy 2, Patrick Rider 1, Lars Bo Jørgensen 2, Henning Bliddal 2, Shane Rabideau 1, & Jens Aaboe 2 - 1 Biomechanics Laboratory, Department of Kinesiology, East Carolina University, Greenville, NC, USA 2 The Parker Institute, Department of Rheumatology, Copenhagen University Hospital, Frederiksberg, Denmark 32 participants (18 females, age 57 yrs, BMI 27.1 kg/m 2 ) with physician diagnosed tibio-femoral knee OA were randomly assigned to strengthening or non-training control groups after providing written informed consent. All participants were pre- and post-tested over a 12 week interval with WOMAC (pain and function), isokinetic quadriceps strength, 3D motion capture, and force platform instruments. Strength training consisted of supervised leg extension, leg press and lunge exercises (fig 1) three times per week with three sets of ten repetitions and loads increasing from 65% to 80% of 3RM. Maximum quadriceps force, power and total work and tibiofemoral contact forces during stair ascent and descent were assessed with a biomechanical model (1). Data were analyzed with two-way ANOVAs (Group by Time) for ascent and descent with Tukey post hoc tests following significant interactions, all at p<0.05. Despite significant improvements in quadriceps strength, pain, and function in the strength training group only, no significant interaction, group, or time effects were observed in maximum quadriceps force, power, work and knee loads in either stair ascent or descent. Our data refute the concept that the mechanical function of the quadriceps muscle in locomotion is altered after quadriceps strengthening in knee OA patients. Improvements in pain and function following quadriceps strengthening are therefore not due to altered quadriceps or knee biomechanics during daily activities but to another, as yet unidentified mechanism. 1. Messier, et al, Osteoarthritis & Cartilage, 2011 Figure 3 – Mean quadriceps strength. # = significant group x time interaction, p Pre, Trained only, p<0.05 Figure 4 – WOMAC pain & function. # = significant group x time interaction, p<0.05, * Post < Pre, Trained only, p<0.05 Figure 5 – Stair Ascent: Quadriceps force & power and knee contact force. Solid lines represent pre-test means, dashed lines represent post-test means, and dotted lines represent one pre-test SD Figure 1 – Strength training exercises.Introduction Results Methods Conclusion References Figure 2 – Stair ascent & descent simulations & videos #, * Quadriceps Force Tibio-femoral Contact Force Quadriceps Power Figure 6 – Stair ascent and descent maximum forces and powers. There were no significant interaction or main effects for these variables, p>0.05. AscentDescent Quadriceps Force Tibio-femoral Contact Force Quadriceps Power Descent Ascent Lab website Lab facebook