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dennis.torre
03-19-2011, 03:25 PM
I am a movement science graduate student and in our 2D kinematic lab class I noted that maximum angular velocity tended to occur near the mid position for motion in either a flexion or extension direction. Does the joint angle for maximum angular velocity always occur near mid range or is it dependent on such variables as amount of external load or velocity of movement? Also, is the joint angle for maximum angular velocity altered when there is injury and does it have any diagnostic value in predicting eventual tendon or joint pathology? Thank you!

bogert
03-20-2011, 02:46 PM
Dennis, there is a theory that people choose movement patterns according to "minimal jerk". Jerk is the 3rd derivative of position. If a movement starts and ends with zero velocity, the trajectory of minimal jerk is a 3rd order polynomial and it will have its maximum velocity exactly halfway in the movement.

The minimal jerk hypothesis was introduced in a paper by Flash and Hogan, Journal of Neuroscience 1985.

If you observe that someone does not have the maximal speed at the point predicted by this theory, it could be that the theory is wrong, or that the person has not yet developed the skill to perform the movement optimally.

Ton van den Bogert

dennis.torre
03-22-2011, 12:35 PM
Dennis, there is a theory that people choose movement patterns according to "minimal jerk". Jerk is the 3rd derivative of position. If a movement starts and ends with zero velocity, the trajectory of minimal jerk is a 3rd order polynomial and it will have its maximum velocity exactly halfway in the movement.

The minimal jerk hypothesis was introduced in a paper by Flash and Hogan, Journal of Neuroscience 1985.

If you observe that someone does not have the maximal speed at the point predicted by this theory, it could be that the theory is wrong, or that the person has not yet developed the skill to perform the movement optimally.

Ton van den Bogert
Dr Van der Bogert,
Thank you so much for responding to my question and guiding me to the minimal jerk hypothesis.
I looked over the Flash & Hogan (1985) article you referenced. In their discussion, they mention that minimal jerk most likely did not evlove to minimize system wear & tear since it is observed during movements of moderate speed. But interestingly they also mention that jerk movements are independent of neuro-muscular dynamics as long as the activity demands lie within the neuromuscular capacity of the system, and do hint at prediction between kinematics & neuromuscular dynamics as the boundaries of performance are reached such as during rapid movements. Can you please provide further direction with regards to the following question: does assessing jerk at high angular velocities have the potential to predict risk for joint injury? Additionally, are you aware of any research in this area, or of the effect of injury (i.e ACL tear) on minimal jerk?
Thank you,
Dennis

bogert
03-23-2011, 10:06 AM
The minimal jerk idea has been used in research on motor control, it is basically the idea that skilled movements are smooth. I am not even sure if that idea is still used. I am not an expert on motor control. It does explain nicely your observation that peak angular velocity occurs halfway in a movement.

I know of no research that links this to injuries. I would be hesitant to make such a link. The biomechanics of injury is usually studied with variables such as forces and moments, which are much more directly linked to mechanical stress on tissues. The only possible link, to me, is that high jerk may be an indication of less skill in performing the movement.

If anyone has better information, or other opinions, please post here.

Ton van den Bogert

dennis.torre
04-07-2011, 02:18 PM
The minimal jerk idea has been used in research on motor control, it is basically the idea that skilled movements are smooth. I am not even sure if that idea is still used. I am not an expert on motor control. It does explain nicely your observation that peak angular velocity occurs halfway in a movement.

I know of no research that links this to injuries. I would be hesitant to make such a link. The biomechanics of injury is usually studied with variables such as forces and moments, which are much more directly linked to mechanical stress on tissues. The only possible link, to me, is that high jerk may be an indication of less skill in performing the movement.
If anyone has better information, or other opinions, please post here.

Ton van den Bogert

Thank you for your last reply. Dr Van Der Bogert. I recently came across an article by Yan et al (2000) which supports your view that high jerk may represent less skill ability. In this study the researchers measured jerk in children during a throwing activity using a 2 camera video system. The researchers found that as children age, not only did their peak ball velocity increase but their normalized hand jerk decreased. Interestingly, they also noted that at faster throwing velocities, jerk decreased in 6 year olds but increased in 3 year olds. In their discussion, the authors mentioned that jerk may respresent temporal coordination and may be a useful indicator of throwing performance in children.
However, I have yet to locate any literaure on changes in jerk with injury or fatique.
If anyone is aware of other clinical implications of jerk I would greately appreciate it.
Thank you,
Dennis