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Date: Wed, 10 Sep 2003 19:54:47 -0000

From: " paultheo2000 " <paultheo2000@...>

Subject: Re: exercise - strength vs. power

Well, the terminology used here is not quite correct. Power, in

weightlifting, refers to the physical notion of power. (All this is

brilliantly explained in Siff's book).

Strength requires power, because an object MUST be moved from rest.

Because it's initial velocity is zero, an acceleration, and by

defintion a force is necessary. (If a force is present, work is

present, and power is present).

You can also achieve great deals of power without being very strong.

(Again, many definitions of 'strength' have been given using

isometrics, isotonics, isokinetics, etc). Differences in neural

potentiation account for all this.

-

--------------------------------------------------------

, let's look at this from another angle.

I see what you are saying here, and from a certain point of view it

may be correct, but try this on for size:

A physiologist would define the strength of a muscle as the maximum

force a muscle can exert (along it's longitudinal axis).

An athlete is more interested in defining strength as that force that

a muscle can exert on an external object (e.g. a dumbell loaded with

weights).

(Another consideration in muscle strength is the angle of pull----and

the length of the muscle when it contracts to produce the force,

versus the muscle's resting length. A muscle will vary in the amount

of force it can produce depending upon the joint angle).

Power can be defined as Force X Velocity.

Since Velocity is distance/time, and Force X Distance is the

definition of Work, then Power may also be defined as Work/time.

Increased Power would be manifested for example as moving a weighted

object a certain distance divided by the speed.

Let's say that a 200# individual does a vertical jump of 4 feet in 1

second. He then performed 800 ft-lb of work in 1 second (200# X 4

ft), or 48,000 ft-lb of work/min. This equals 1.45 horseower of work

(1 hp= 33,000 ft-lb/minute. Of course, this reflects only the power

of some of the muscles in the body---the muscles that were used to

perform the work.

You said that " If a force is present, work is

present, and power is present. "

This is certainly true for the example that you gave of moving an

object from rest.

However, Work is force times distance, so it is not true in all cases

that if a force is present, work is present. If you push against a

building as hard as you can with both hands, but do not move the

building a certain distance, No work has been performed, and there

was no power. No Work means no Power.

And yes, certainly there are isometric (the length of the muscle does

not change as it produces force) contractions, isotonic contractions

(constant external resistance, such as biceps curls with a 60#

dumbbell), both concentric (the muscle produces force while the

muscle length shortens) and eccentric (the muscle produces force

while the muscle lengthens), and isokinetic (same speed)

contractions, both concentric and eccentric.

The post would be way too long if we went into details regarding

static vs. dynamic strength; isometric, isotonic, and isokinetic; and

concentric vs. eccentric contractions (many people who belong to gyms

call eccentric contractions " negatives " , if that clarifies anything.

Thank you

Bob Bessen

p.s. some of this material was taken/stolen from The Biology of

Physical Activity, by Edington and Edgerton (I was fortunate to have

taken exercise physiology from Dr. Edgerton at UCLA), and from

Athletic Training and Physical fitness, by Dr. Jack Wilmore--all

three authors PhD's (exercise physiologists), not M.D.'s.

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