View Full Version : Re: Optimum hip and knee joint angles for generating power

David Smith
10-04-2006, 06:10 AM

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

----- Original Message -----
From: "Andrew Lyttle"
Sent: Wednesday, October 04, 2006 7:59 AM
Subject: [BIOMCH-L] Optimum hip and knee joint angles for generating power

Hi All,
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.
Regards, Andrew

Andrew Lyttle
Sports Biomechanist

Western Australian Institute of Sport
, alyttle@wais.org.au