Maybe I am getting boring to some people with my “running” topics but, trust me, there is almost no more complex movement than running and walking both – therefore a new inspiration never dies! Such a natural movement but so complex…
I see very often almost-straight leg sprinting among athletes. It’s mechanically an inefficient movement. Can you imagine a gymnast who performs a bar swings (acceleration just before the final jump) with extended hips in the upper positions? No, because if you want an efficient (faster) swings (circles) you must to bent your hips (hip flexion). Simply, lever (whole body except hands in this case) is shorter on that way and become easier to catch (gain) and maintain high circular velocity!
It’s a same situation in sprinting, you need as fast as possible legs circles below a trunk (legs moving in sprinting). You will gain that if you bend your hips (knees must reach the height of the hips or little below). Plus you need to bend your knees with most of your in-the-air leg swing phase (shorter lever – faster movement, great mechanical advantage). On that way, your legs become faster (moment arm is lower).
One more thing, with almost-straight legs sprinting your hip flexors need to work harder because of longer lever. Poor hip flexors 🙁 … Plus frontal air resistance is a little higher in the almost straightened knees and plantar flexion position (both undesirable in sprinting).
Last but not least, every included muscle works on best mechanical way with technique mentioned above (easier and faster movement with maximum force production – at contact and swing phase both). Also, you can lengthen stride a little bit with this technique.
It makes sense to utilize this advantages because you need as fast as possible limbs in sprinting. Otherwise, this is not a proper track and field sprinting technique accidentally, any serious sprinter owns that one – nothing new 🙂 .
Thanks for reading and all the best,