If you enjoy running, but nagging knee pain prevents you from getting your weekly mileage fix, try recalibrating your trunk flexion angle. What is trunk flexion angle you ask? Your trunk flexion angle is the bend at your hips or how far your pelvis and torso are from vertical. A recent study by Teng and Powers (2014) found that increasing the average subject’s trunk flexion angle by 6.8o while running at a controlled speed results in a 6.0% decrease in patellofemoral joint (PFJ) force and reduces torque produced by the quadriceps. On the opposite end of the spectrum, running more upright than one’s self-selected trunk flexion angle [closer to a vertical trunk posture] increases PFJ forces 7.4%. If sagittal plane [side view] mechanics are one of your most salient flaws, this may be a slam dunk for eliminating knee pain.
What does the evidence really mean? The underlying premise is that increased peak forces at the PFJ contribute to mechanical trigger for knee pain. Despite a lack of longitudinal studies to prove this strategy reduces knee pain, one could make the argument that a small reduction in PFJ forces with each step over the entire course of a run is significant. Anecdotally, I have seen this work.
Applying this concept to your running can be difficult without visual feedback. You can get a close estimate of your trunk flexion angle using a mobile motion capture app such as Ubersense that allows you to draw angles on video captured on your smartphone or tablet. Keep in mind that your speed may affect trunk flexion angle. In the current study, subjects ran at 3.4m/s [7:53min/mile]. Trunk flexion angles between 10o and 18o were associated with reduced PFJ peak forces whereas angles of 1-7o were associated with higher peak PFJ forces.
My advice is to learn trunk flexion angle on a moderately steep hill [~10% grade]. Lean forward slightly from your ankles first, then your hips, and you just might find your gluteal muscles. In my experience, teaching people to run uphill and downhill more efficiently with effective trunk lean and cadence for each task can decrease mechanical stress at the PFJ and in turn, reduce the trigger for mechanical knee pain. Happy running!
Teng HL, Powers CM. Sagittal plane trunk posture influences patellofemoral joint stress during running. JOSPT. 2014; 44: 785-792.