I enjoy watching Donnie Yen kick a man in the face as much as the next guy, but consider the mechanics of this kick. There's a lot going on, but every single joint from his neck to his toes is involved in the kick — that means that every single joint is contributing to the power of the end-result, but is also contributing to kind of DOMS Donnie will be feeling tomorrow, and the long-term recovery after this fight, and after a career of fighting.
Not everyone who participates in martial arts will be doing moves like this, but I wanted to use this specific kick from Ip Man to illustrate the kinds of biomechanics that martial artists face, and how to prevent those forces from causing chronic injury. To do this, I'm going to walk through this kick from head to toe.
DISCLAIMER: I am not a martial arts instructor, and I do not intend for this article to be prescriptive in the practice of any martial arts. Rather, this article is intended to provide an example of the forces of biomechanics at work in martial arts.
Head is rotated & laterally-flexed
Simply put, he has to move his head to look at his foot so he can see where he's kicking. Although this is a very wise decision, it does put strain on the muscles and joints of the neck. Holding this position, or moving through this position frequently will shorten the muscles on the left-side of his neck. Without stretching & strengthening exercises, this could cause chronic neck pain and/or a nerve-pinch.
There is a rotation through the spine
He has decreased the rotation by dropping his right shoulder (presumably into the nose of his other opponent), but there is still a notable twist, evident by his hips and shoulder not being square. Rotation through the spine causes the facet joints of the spine to compress the spinal discs. The impact of the kick puts the already strained disc at risk of herniation. Serious core-strengthening is required to decrease the risk of these types of movement causing problems.
His standing leg fully-flexed through the hip and knee
This allows for the maximum amount of force to be transferred to the kick, but puts a strain on the adductors of the grounded leg. Muscle strains, tears, and ruptures are all possible in this position, but regular conditioning of the adductor muscles and the opposite hip rotator with limit the possibility of injury.
His kicking leg is at a postereolateral angle (it is extended behind him, at a side-angle)
Kicking at this angle contracts muscles of the leg, hip, and lower back. So long as these muscles are conditioned properly, it makes for a very powerful kick indeed. However, if the muscles are weak or not warmed-up correctly, the muscles can spasm and the pelvis and/or sacrum will subluxate causing long-term, chronic back pain.
His kicking leg is bent slightly at the knee
Like I stated before, I'm no expert, but I think this might actually be a mistake. Bending the knee during a kick like this decreases the power of the kick (as some of the impact is absorbed by the knee), and it also allows the impact of the kick to over-load the hamstrings. So long as the hamstrings are strong and warm, this will cause to immediate injury, but it will cause the hamstrings to shorted and proper stretching in the recovery period is crucial to avoid long-term hip dysfunction and lower back pain.
His ankle is straight, and he's striking with the sole of his foot
This allows the impact of the kick to hit the lower leg evenly, not causing injury to the ankle-stabilising groups (the peroneals and the tibial group), or to the bones of the foot and ankle.
As you can see, biodynamics is complex, but entirely crucial in martial arts. Strength and conditioning is as important, if not more important than learning form.
If you want more information on martial arts injuries, email me directly via the contact page. If you want specific information about your own injury or if you're after treatment for an injury, contact one of my clinics directly to make an appointment. Details of those clinics can be found here.
To start learning how to practise injury-free martial arts, contact Melbourne Wranglers Wrestling Club, or Melbourne Dragons - both are inclusive sports clubs and both enjoy support from me as a vollunteer sports trainer.
Dr Mitch Clark