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alyttle62
10-15-2006, 06:24 PM
Hi All,
Many thanks to all of those that responded to my original question of the optimum knee and hip angles for development of force and power. Its still appears to be an area that there has been little conclusive research into the exact combination of joints that produce the great force output or rate of force development over a large movement range. I have added the reply summaries onto this email.

Original Query:

I am interested in the results of any research into the optimum knee and hip joint angles for generating explosive power from a static position (or combinations of hip and knee joint angles if this has been investigated). I am also interested in approximate percentage decrement as you deviate from these angles (eg. is there say a 20% decrement in rate of force development with a 30 degree change in knee joint angle???). This has particular relevance to numerous sporting situations such as the dive start position in swimming and the rugby scrummaging set position. Any information would be appreciated and a summary of replies will be sent out.

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Replies:

This article looks at pedal crank lengths, but reports on corresponding power outputs and hip/knee/ankle angles. Hope it proves helpful.

Too, D. & Landwer, G.E. (2000) The effect of pedal arm crank length on joint angle and power production in upright cycle ergometry. Journal of Sport Sciences, 18, 153-161.

Regards,

Stephen Dixon
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My name is Stepehn Cousins I am a Research Fellow at the University of East
London. I have done numerous research projects on the sprint start, much has
been investigated on optimum hip, knee and ankle angle angles in order to
increase force output during the sprint start (as this is seen as the
defining characteristic in measuring start performance). It has been stated
that knee angles between 90-120 degrees, hip angles between 35-45 degrees
and ankles angles of between 80-115 degrees can optimise the force output
during the performance of a sprint start. I don't have these articles at the
moment but I've listed ones that might be of use to you below.
I hope this helps. I would be very interested to read about any findings you
make.
Stephen Cousins

Atwater, A. (1982). Kinematic Analysis of Sprinting. Track and Field
Quarterly Review. 82(8), 12-16.
Baumann, W. (1976) Kinematic and dynamic characteristics of the sprint
start. In: Biomechanics VB. P.V.Komi (Ed). Baltimore: University Park Press,
194-199.
Cousins and Dyson (2004). Forces at the front and rear blocks during the
sprint start. XXIInd International Symposium on Biomechanics in Sport,
198-201.
Harland and Steele (1997). Biomechanics of the Sprint Start. Journal of
Sports Medicine, 23(1), 11-20.
Jackson and Cooper (1972). Effects of hand spacing and rear knee angle on
the sprinters start. Reasearch Quarterly. 43(3), 378-382.
Mendoza and Schollhorn (1993). Trainig of the sprint start technique with
biomechanical feedback. Journal of Sports Sciences. 15(2), 149-152.
Mero, Luhtanen and Komi (1983). A biomechanical study of the sprint start.
Scandinavian Lournal of Sports Sciences. 5(1), 20-28.
Roberstson (1986). Contributions to the ankle and knee muscles on sprint
starting. Proceedings of the North Americam Congress on Biomechanics, 2,
235-236.
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Its an interesting question but I have never read any such research
regarding specific sports. I imagine it would be fraught with difficulties.

There is a lot of research regarding force and power out put of hip and knee
using dynamometers http://www.springerlink.com/index/U40Q84X505982207.pdf
is a link to one for instance. But to find more just search using key words
knee hip power force dynamometer.

Using force plate and 3D video would be another way of characterising max
grf force v's limb position during a certain action of interest. Max force would = max acceleration and therefore max power perhaps.

Just my thoughts but I think it would first be useful to define what is
meant by explosive power.
Power = rate of work 'explosive' is redundant since this implies a massive
increase in work rate ie power.
Perhaps you could be looking for an explosive increase in force. Force =
mass x acceleration since it is unlikely the mass of the athlete will change
perhaps you are looking for rapid acceleration of the body mass. For example it is usual in biomechanics of gait to measure power at the
joint of interest and is defined as a scalar product of ang velocity x
moments. This sounds useful but only really gives comparative data. This is
because even if the muscle is producing a lot of force it is not necessarily
causing a joint rotation ie isometric contraction. This type of muscle force
may be very useful in a rugby scrum but not so useful in a dive from the
pool side.

Do you want the power to move a small mass over a long distance or ar large
mass over a short distance in a given time.

Perhaps you could ask what ankle, knee and hip joint angles produces the
highest acceleration of the body mass.
So therefore you could reach the required terminal velocity in the shortest
time. These angles may be dependent on the direction of the force required.
For instance pressing a weight above the head would require max vertical
force but a American football player would require max force in the
horizontal plane to stop a running forward player.

There is data about the relation of muscle length v's muscle force however
this has many variables such as concentic v's eccentric contraction. If one
could define the optimum force / length out put of a certain muscle of
interest then it may be possible to equate that to a joint angle, however
one would first have to define the firing times and magnitude of that muscle
or group of muscles and this is a very grey area.

In jumping/ bouncing activities the force is often generated by elastic
energy of large tendons eg achilles tendon.
Power lifters though increase force and power by increasing the efficiency
and size of the muscle, olympic lifters use a combination of both. .

Cheers Dave Smith
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Regarding a study by Ken Quarrie (New Zealand Rugby Union) on force production during scrummaging:
They did not find much of a relationship between body alignment and the force that players were able to produce on an instrumented scrum machine.

The mean angles at the ankle, knee and hip of individuals when pushing on the scrum machine were 282 * 11, 108 * 13 and 237 * 25 respectively. The correlations of the ankle, knee and hip angles to individual scrummaging force were 0.2, 0.02 and -0.28 respectively. Subsequently, the effect of interactions between each of the angles on scrummaging force were examined. This was to see whether an 'optimal' combination of angles for producing scrum force existed (the idea being that angles less than or greater than a certain optimal joint angle may have reduced force production). No combination of ankle, knee and hip angles was able to account for a significant proportion of variation in the force, nor did higher order interactions (quadratic terms) of a single joint bear a significant relationship to scrummaging force.

It may have been that there was not that much variation in position (I don't have a feel any more for how much of a difference the reported variability in position actually represents) because players were typically well coached and adopted similar positions. Had we constrained the players to particular positions we may well have seen some relationship.

Ken Quarrie

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Conrad Pearson (siliconCOACH Ltd - Australia) investigated the effects of changing knee and hip flexion angles and squat jump performance. Sixteen competitive swimmers (7 male, 9 female) had their squat jump performances tested over a range of knee and hip angle combinations. Knee angles ranged from 140 degrees to 80 degrees, hip angles ranged from 140 degrees to 65 degrees with changes in 15o increments. Based on the findings of this study it was concluded that:
* The greatest jump heights for males were obtained using a knee angle of 95 degrees and a hip angle of 80 degrees.
* Females reached their greatest jump height at a knee angle of 140 degrees and a hip angle of 80 degrees.
* Increases in hip and knee flexion generally elicited increases in jump height and movement time and decreased peak force.
* Reaction time and movement time did not differ between any of the joint angle combinations (p > 0.05).
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Andrew Lyttle

Sports Biomechanist
Western Australian Institute of Sport
alyttle@wais.org.au