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Economy and movement

In economy of movement lies efficiency. However economy might mean something different to other people. Today I had the privilege to listen to a lecture presented by Nobel laureate and professor in Economics at Columbia University Josef Stiglitz. His lecture was about different economical models, and his thoughts on what constituted a good one. Two models, one on each end of a spectrum, can be used to explain differences between different economical models. On one side one model would be highly regulated, while the model on the other side, the free market, would not be subject to such regulations and the market forces would dictate. Professor Stiglitz argued that the free market would create inequalities and gave numerous examples of this. I could not help myself to think of human movement.

 

In order for the body to function optimally, or other systems for that matter, there must be equality between different regions and joints. The use of equality here refers to different joints and regions contributing, based upon their abilities, to the overall performance of the body. As soon as one part, whether that be region, joint or muscle group, disproportionally contributes to the movement there will be trouble. The result could be injuries or a less efficient movement. Did not efficiency reflect movement economy?

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The kinetic chain and throwing

One hears the word shoulder rehabilitation and testing for athletes involved in throwing. This is also true for athletes involved in hitting an object with an instrument such as a racket. In the presence of dysfunction and pain in the shoulder isolated tests and exercises are commonly performed. This can be very helpful, however in order to treat for dysfunction and enhance performance in throwing one has to understand the contributing factors to the speed of the ball. In order to do so the entire kinematic chain has to be analyzed. Therefore to treat and train for throwing performance one has to be an expert on the entire kinematic chain.

The importance of the integrated kinematic chain in throwing can be exemplified by throwing in water compared to that of on the ground. Throwing in water polo is very different than handball. The speed of the throw in water polo is slower than that in handball, and we have to ask ourselves why is this. The ground certainly has something to do with this. As we are performing the throw, different joints from the ground to the hand will contribute rotational energy that ultimately leads to the speed of the ball.

Toyoshima and colleagues performed a simple analysis of segmental contribution to throwing in 1974. They imposed restriction of movement of different segments in the body while throwing. As motion in the lower extremity and trunk was restricted speed of the ball decreased by 60% when throwing. Then one might say that this is obvious, and it is. However, the obvious is not implemented in testing, rehabilitation and training of the shoulder. No wonder we end up with dysfunctional shoulders.

Jessica, Ali and Ola

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The effect of antipronation orthotics on ankle and subtalar joint kinematics

This is a short summary of a recent study Liu and co-workers published (2012) a study the effect of antipronation orthotics on ankle and subtalar joint kinematics. Some of our experience and knowledge is also added to the summary of this article.

Orthosis are fabricated to control rearfoot, ankle and subtalar joint, pronation. It has been found that the amount of subtalar joint eversion and abduction is reduced with 1-2°. This is only describes the amount of motion, but not the rate at which this is happening. Eversion and abduction velocity is therefore also studied, since this reflects the rate of loading of muscles and tendons. Traditionally these motions are considered to take place at the subtalar joint, however we know this not to be true. Studies have shown these motions are also taking place in the ankle, talocrural joint, and sometimes to a greater extent than at the subtalar joint. This might be due to individual anatomical differences, tibia/fibula geometry or stiffness of ligaments and capsules. Understanding what joints are controlled with orthotics is important since this can help us understand why orthosis are effective in some individuals while ineffective in others. The purpose of the study was to see if antipronation orthotics would impact the amount and rate of pronation and how the subtalar and ankle joint were affected.

Five subjects were recruited. A 4° medial rearfoot wedge were used for all subjects Intracortical pins were used in this study. This is the most accurate form of motion analysis, in that pins are drilled into the bones, rather than placed on the surface of the skin. A 12-camera motion capture system (Qualisys) was used to obtain the kinematic data at 240 Hz. The data was analyzed in Visual 3D with a standard definition of joint axes. Cardan angles were then calculated (sequence x, y and z). The data was recorded for five walking trials, however no mention of speed of the different subjects was made.

The results show that there are individual responses to anti-pronation orthosis. There was a reduced peak and range of rearfoot eversion and, to a lesser degree, abduction relative to the leg.

From the discussion we would like to quote the authors; there are many interrelated variables affecting subtalar and ankle kinematics, and therefore, a systematic kinematic response to a foot orthosis seems unlikely. The role of the orthosis cannot be to adjust foot position or motion to achieve a single optimum kinematic pathway or foot position as current orthotic paradigms suggest (based on concepts de- scribed in Root et al. [11]). Rather, the orthosis influences the external loads that determine the person-specific foot kinematics, and as a result, the orthosis causes the joints of the foot to pass through adjusted versions of a person’s underlying kinematic pathways.

Then authors conclude that; The antipronation foot orthosis produced small and un- systematic reductions in eversion and abduction of the heel relative to the leg at various times during stance. This was achieved via complex changes at the ankle and subtalar joints that were specific to each subject tested. These changes contradict existing orthotic paradigms and are indicative of a strong interaction between the ankle and subtalar joints.

We feel it is necessary to comment on this study and raise some important questions. In many scientific studies interventions or treatments are given to a group of subjects regardless of need. This is also the case here. Did all five subjects really need a 4° medial rearfoot wedge? We know this might be difficult to determine who needs what, but there is a need to have tests that can identify who needs what and why. Furthermore it would nice to have more information of how many steps were recorded, if only the right foot was recorded, and if so what was worn on the left foot, what was the average walking speed and range of walking speeds and why only five trials were recorded. We know that there is great variability between steps and the number of steps analyzed is important information in this regard.

Regardless of these comments, it is an interesting study pointing to important aspects of foot function and the use of orthosis