Guest guest Posted September 12, 2003 Report Share Posted September 12, 2003 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. Quote Link to comment Share on other sites More sharing options...
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