Due to the comments in KaratebyJesse.com, I was inspired to determine the best area of the foot for the pivot point. The best pivot point was be based on minimizing injury to whoever was pivoting.  Three different pivot points were looked at:  The heel, the ball of the foot near the big toe (1st and 2nd metatarsal heads) and the entire ball of the foot (heads of metatarsals 1-5.)  The information used was based on injuries in competitive athletes and dancers as well as modeling using existing information.

There were three areas where pivoting caused injuries, these include the ankle, bones of the foot, and the knee.  While it is difficult to assess which is the preferred way to based on personal experience, it becomes overwhelmingly obvious when how injuries occurred and the frequencies of injuries are used for evidence.  The self-evident conclusion was that the preferred pivot point was the head of the 1st metatarsal (point that the big toe joins the ball of the foot.)

 

Common foot injuries:

The main injuries of the foot caused by a rotational force are ankle sprains, and the fractures of the 5th metatarsal.  “Lateral ankle sprains are among the most common injuries incurred during sports participation…typically occur when the rearfoot undergoes excessive supination on an externally rotated lower leg…” (Hertel).  As the most common injury of the foot would be found with the heel as the pivot point it is glaring that this would be among the worst pivot point

Another common injury of the foot is called the Dancer’s (or Jone’s) fracture.  This fracture occurs due to mis-alignment of the foot during a rotation or landing on the lateral (outside) side of the foot.  It has an incidence rate of 1.8/1000 and can be prevented by maintaining the weight on the 1st and 2nd metatarsal heads rather than on the 5th.   This leads to a noticeable conclusion that using the lateral side of the foot to be a poor location for a pivot point.

There is one fracture of the 2nd metatarsal which is caused by repetitive over-usage and severe weight barring called a “March’s fracture.”  As this fracture is limited only to over-usage it can be excluded from this research.

 

Knee injury:

Knee injuries are common in many sports; these can be classified into traumatic and non-traumatic.  As the question is on pivoting, the traumatic injuries were neglected, only non-traumatic were used.  In the clinical world, it is commonly accepted that non-traumatic injuries of the knee tend to occur due to rotational shear forces on the ligaments.

The force that cause Anterior Cruciate Ligament (ACL) tears,  “… were 100 N of anterior tibial force, 10 Nm of varus and valgus moment, and 10 Nm of internal and external tibial torque…”  (Markolf  et al)   So the force needed to get an ACL tear is about 10 Nm of force (80lbs per inch)which is easily produced by rotating.  With the rotation at the heel, there is an increased risk of this torque on the knee not seen if using the ball of the foot.

 

Conclusion:

As the numbers of injuries seen using the ball of the foot near the 1st metatarsal are minimal, it becomes obvious that it is preferred to protect the body.  It was interesting to note that the preferred pivot point in professional dancers, especially ballet dancers is the same pivot point that is preferred based on the longevity of the knee and ankle.  The disabling injuries of the knee due to rotation on the heel make that pivot point absurd when compared to the other two.

 

Discussion:

One point that was not addressed is the surface area between the foot and the ground in each pivot point.  No research was found on that topic but using basic modeling, we find that the average point of contact between the heel and floor versus the ball of the foot at the 1st metatarsal is a differences of almost three times.  As friction’s effects are exponential rather than linear, it may be the reason that more ankle and knee injuries are noted using the heel as a pivot point.

Some of the injuries mentioned can cause a decrease in quality of life and lead to rupture of the ligaments which would need reconstructive surgeries.  As sprains and strains tend to re-injure, it would be rational to use methods of pivoting that would avoid or minimize these injuries as much as possible.

 

References:

  1. Kadel, Nancy J.  MD, Foot and Ankle Injuries in Dance, Phys Med Rehabil Clin N Am  17 (2006) 813–826
  2. Renstrom P AFH, Konradsen L. Ankle ligament injuriesBr J Sports Med.1997; 31:11–20.
  3. Cortes N, Quammen D, Lucci S, Greska E, Onate J., A functional agility short-term fatigue protocol changes lower extremity mechanics.,  J Sports Sci. 2012;30(8):797-805. doi: 10.1080/02640414.2012.671528. Epub 2012 Mar 19.
  4. Venesky K, Docherty CL, Dapena J, Schrader J. Prophylactic ankle braces and knee varus-valgus and internal-external rotation torque. J Athl Train. 2006;41(3):239–244.
  5. Markolf, K. L., Burchfield, D. M., Shapiro, M. M., Shepard, M. F., Finerman, G. A. M. and Slauterbeck, J. L. (1995), Combined knee loading states that generate high anterior cruciate ligament forces. J. Orthop. Res., 13: 930–935. doi: 10.1002/jor.1100130618

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