Re: Muscle work

[S Goelzer <sgoelzer@EARTHLINK.NET>]

Having lifted weight for 15 years, I have a problem with the freefall model.
It does not fit the conditions of the problem given and in practice will
destroy joints due to the jolt caused by stopping the falling weight. Moving
the weights (or whole body) at constant speed on the both positive (up) and
negative (down) at constant speed is considered to be good form.

Why does it feel different? My opinion is that when I am trying to maintain
this ideal of constant speed the positive stroke requires that I transfer my
chemical potential energy into gravitational potential energy (simple view
of the main process). It becomes hard when I deplete the stores of CPE
energy. Failure occurs when little is available.  On the neg. stroke (many
consider this to be the most important in muscle gain since the speed of
descent can be lengthened considerably) I must maintain a constant speed,
but I must absorb GPE energy from the weights. The difference is that the
weights will always provide energy on the way down, not so on the way up.
This allows me to complete the negative stroke no matter what - easier
mentally. Some electronic weight machines (the brand name escapes me - Life
something) actually are programmed to take advantage of this and provide
about a 10% increase in load during the negative stroke.

Also-
A pullup is a complex motion from a weightlifters view point. No one set of
muscles is isolated. Different muscles come into play at different points in
the motion. Completing (point just before the max. height) a pullup requires
considerable strain on the lats (muscles under each arm) since this strain
occurs just at the top of the stroke and lats are typically less developed
than biceps and delts, the downstroke will feel much better as the load is
relieved from those quick to fail muscles back to other stronger muscles.
This can be demo-ed for any student who cannot actually do a pullup by using
a lat pull down machine. This machine will also show how changing the
spacing between the hands gripping the bar will dramatically change effort
required to pull down the bar.

HTH
Scott

on 7/23/01 4:13 PM, Larry Woolf at larry.woolf@GAT.COM wrote:

> Here's my 2 cents worth.
>
> Lift a weight quickly over your head and then lower it at the same speed.
> It is much easier to lower it. Why? Because it is in free fall for part of
> the time while you are lowering it so no work is done by your muscles during
> the free falling time. In contrast. it always requires a force against
> gravity to lift it over your head.
>
> Now decrease the speed at which you lift and then lower the weight.  The
> effort it takes to lift the weight and then lower the weight become more
> similar.  If done very slowly, the efforts are effectively the same.  Try
> the experiment by lifting and lowering a barbell weight (3 seconds up and 3
> seconds down vs. 15 seconds up and 15 seconds down.)
>
> When you lift a weight, there is no way to cheat gravity.  When you lower a
> weight, you can easily cheat gravity when the weight is in free fall.  In
> fact, I suspect that a realistic model for lowering a weight is one in which
> the weight free falls a small distance then you muscles slow down the
> weight, followed by subsequent free falls and catches.  The same holds true
> for push ups and pull ups.
>
> Lawrence D. Woolf; General Atomics; 3550 General Atomics Court, San Diego,
> CA 92121; Phone:858-455-4475; FAX:858-455-4268; http://www.sci-ed-ga.org
>
> -----Original Message-----
> From: Tucker Hiatt
> Sent: Monday, July 23, 2001 9:24 AM
> Subject: Re: Muscle work
>
>
> I've explained why this question bugs me.  (Although Tim Folkerts
> recent posting has helped considerably.  Thanks!)  Please let me also
> explain why it bugs my students.
> Often, the muscle motion under examination is repetitive.  Push-ups
> and pull-ups are particular favorites.  I instruct the students to
> complete each half-cycle of their exercise at constant speed, if
> possible.  (And I acknowledge that we are ignoring the work done
> during turn-around times.)  This means that a student does work
> during the downstroke as well as during the upstroke.  On the
> upstroke of a constant-speed pull-up, the average muscle force
> applied is roughly the student's weight.  On the constant speed
> downstroke, however, the average muscle force is ...???   Mustn't it
> also be the student's weight?  And therefore the (magnitude of the)
> work done is the same?  Doesn't that vivify the question: Why do the
> upstroke and downstroke FEEL different?

--
*****************************
Scott Goelzer
Physics Teacher
Coe - Brown Northwood Academy
Northwood NH 03261
603-942-5531 ext43
sgoelzer@coebrownacademy.com
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