Proper knee mechanics when running can help soak up impact and give you more energy. I’ve talked about how the propulsive phase can be made easy — by pulling, not pushing with your toes — when forefoot running. That was an incredibly useful tip I got from Pose Running.
We now know that greater knee flexion (i.e. bending the knee) at touchdown is a great trick to help a forefoot runner glide through the air and run with greater efficiency, but having knee flexion during the propulsive phase is essential to good running economy as well.
Essentially, you should never unbend your knees when you run. I know this may be a little difficult, especially during the propulsive phase because I have a habit of straightening out the ‘push off’ leg. But, here is why keeping both knees bent during forefoot running can really help performance-wise.
Optimizing Your Knee Mechanics When Running
Numerous reports have concluded that less knee extension at toe-off (i.e. the beginning phase of flight) during running, is beneficial to running economy. Having less knee extension, and thus greater knee flexion to initiate flight during running may contribute to more propulsive force (Moore et al.), because it optimizes leg extensor muscle function and muscle-tendon moments, variables that are important in maximum force production.
In a sense, you generate more propulsive power without having to do much work, just slightly bend your knee to inject a spring into your stride.
In addition, keeping both knees bent during propulsion stops you from excessively bouncing up and down (i.e vertical oscillation) when running. And, by bending both knees during propulsion, may give your calf muscles a break because muscle activation in the lower leg is reduced (Isabel, 2016).
Since runners who excessively unbend their knees during running are more likely to get injured and have poorer running economy, how you use your knees can make the difference between getting injured and running painless and efficiently. Bending both knees offers more relief from impact and is an easy way to drastically boost your running performance.
Moore, I. Is There an Economical Running Technique? A Review of Modiﬁable Biomechanical Factors Affecting Running Economy. Sports Med, 2016; 46:793-807.
Moore IS, Jones AM, Dixon SJ. Reduced oxygen cost of running is related to alignment of the resultant GRF and leg axis vector: a
pilot study. Scand J Med Sci Sports. 2015.
BSc Neurobiology; MSc Biomechanics candidate, ultra minimalist runner & founder of RunForefoot. I was a heel striker, always injured. I was inspired by the great Tirunesh Dibaba to try forefoot running. Now, I'm injury free. This is why I launched Run Forefoot, to advocate the health & performance benefits of forefoot running and to raise awareness on the dangers of heel striking, because the world needs to know.