David Smith

10-04-2006, 06:10 AM

Andrew

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"

To:

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

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"

To:

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