Note from Bill DeSimone:
With some formatting changes, this is the same text as originally done in 2004
Ordering information for the complete manual at the end of the article.
For Greg Anderson.
2.0
Locating
the Hidden Moment Arm
We humans remain animals. Biology talks about us all, something that
can create a lot of uneasiness-or worse.
It implies constraints on human aspirations…
Steven
Vogel1
How are you strong?
Not,
“how strong are you?”, which sounds
like I’m asking how many pounds you can lift.
More precisely, I’m asking, “how does strength express itself?”: how are your strong?
Another
experiment. We’ll use the side raise
again, only this time you’ll need a partner.
Your partner is going to perform the motion, only instead of with
weights, you’ll provide manual pressure at the wrist. You want to provide just enough force to
prevent your partner from moving. You’re
going to note how strong your partner’s deltoids appear at certain points in
the movement.
At
the bottom, with your partners’ hands directly under the shoulder, how strong
does he or she feel?
How
about at midpoint, about halfway up?
Finally,
let your partner complete the motion and lower just slightly from the top. How strong here?
This
is a much more subtle demonstration than with the dumbbells. It’s not as visual, and relies on your
perception of touch, so try not to simply overpower your partner. Again, the partner should do the side raise
slowly and steadily, and you should try to just barely stop the motion.
Regardless
of the size of the deltoid, you’re not imagining it if you notice:
Not
too much strength to start (Figure 2.1A);
Significantly
more in the middle (2.1B);
Less
strength at the top (2.1C).
Strength
Vs. Muscle Torque
Strength
may
not be the best word to use in this case, because it usually implies overcoming
a resistance (actually, resistance torque, as in the previous chapter). What we are actually describing in Muscle
Torque.
The
point of this demonstration is that our muscles don’t exert a constant torque
during movement. The torque expressed by
muscles, especially those that move limbs, varies predictably. As the
muscles contract from their most stretched to their most contracted, Muscle
Torque first increases, then decreases, for every healthy muscle/joint complex (Figure
2.1D).
As
I’ll explain, this is simply how the machine works. It shouldn’t be considered a controversial
statement. But when we explore the
consequences of it, it challenges much of the conventional thinking about
Exercise and exercises, with regard
to concepts like “full range of motion”, angle training, shaping, the role of
machines, free weights, etc.
Muscle
Torque and Resistance Torque
Muscle Torque is a tougher concept
than Resistance Torque. It can be the
most frustrating part of biomechanics, because of a number of confounding
factors. We’ll examine them, but mainly
in context of what we can do about them in the gym.
Recall
that with Resistance Torque, we had a variable Moment Arm and a constant force,
the product of which created a variable torque.
The force in Resistance Torque is usually in the form of a weight; hard
to overlook. The Resistance Moment Arm
is easy enough to visualize, as are any changes to it, once the axis and line
of force have been identified.
The
Muscle side is confusing for several reasons2. First, not only do we have variations in the
Muscle Moment Arm in the course of a contraction, we also have variations in
the amount of Muscle Force; both components vary instead of one. Second, neither is as visible as on the
Resistance side. We can only see the
effects, and then reverse-engineer back to a model (although a well-established
one). Third, the Muscle Torque pattern
is not constant. For a given individual,
it can change from training, speed of movement, fatigue, not to mention factors
that are out of our control like neural factors and fiber arrangement. It does, however, change predictably. And finally, Muscle Torque effects overlap
and interface with Resistance Torque effects, so we have to make a point of
first distinguishing between the two, then manipulating the two to our
advantage.
Muscle
Moment Arm
What we are ultimately trying to get
at with any form of strength training is the force-producing capability of
muscle; whether it’s to increase it, as in pure strength training, or to use
it, as in bodybuilding or toning. But
since we’re not in the habit of cutting our limbs open, and attaching a weight
directly to the tendon, we have another Moment Arm to deal with. This Muscle Moment Arm is created at your
joints, where the tendon attaches to the limb that’s going to move. Remember, a Moment Arm is the perpendicular
distance between axis and line of force.
In this case, the axis is located at or near your joints, the line of
force is represented by the tendon, and the force is provided by your muscles.
When
the muscle is at its least concentric position (ie fully stretched), that line
of force lies almost through the axis. A
minimal Moment Arm is created, and so minimal torque is possible. At the most concentric position, the extended
line of force also lies almost through the axis; again, a minimal Moment Arm
and minimal torque. Somewhere in the
middle, the line of force lies as far away from the axis as it can, creating a
Maximal Moment Arm and in turn a Maximal Muscle Torque3. (Figure
2.2)
The
Model for Muscle Force
This change in Muscle Moment Arm would
create a variable Muscle Torque, even if Muscle Force remained constant. As it happens, however, Muscle Force itself
is also subject to variation within a given contraction. The accepted model for muscle contraction is
the “sliding filament”. Without getting
too microscopic: muscles are made up of
fibers, which in turn are made up of myofibrils, which in turn are made up of
sarcomeres, which is the point of the mechanism for contraction. The pattern of force produced at each level
doesn’t differ from the
pattern
of the previous level; so that what happens at the muscle level reflects what
happens at the sarcomere. At the
sarcomere, the filaments actin and myosin don’t contract, but overlap; the
contraction is the result of the filaments sliding by each other. The force of the contraction depends on the
amount of overlap. Minimal overlap
results in low force. Maximum overlap
again results in low force; there is nowhere for the filaments to go. Somewhere in between, there is an optimal
overlap where the greatest force is generated, the “favorable length” 4. (Figure 2.3)
Muscle
Torque Patterns
As it happens, both of the primary
factors in Muscle Torque change in the increase/decrease pattern, as the muscle
contracts from most stretched to most contracted. In terms of what we do in the gym, this means
we are strongest somewhere in the mid-range, which begs the question, mid-range
of what? The range of muscle action
probably exceeds a safe joint range, which probably exceeds the useful range of
an exercise. Or not, which is why in
coming chapters we look at each muscle and joint complex separately, and design
exercises to stay in a safe range for the joints while loading the range of
Maximum Muscle Torque.
For
now, let’s continue to explore Muscle Torque.
Figure
2.4A is a graph approximating Muscle Torque.
In the course of a set, the curve would shift downward, as fatigue is
one of the factors affecting Muscle Force.
Is it possible to have Muscle Torque in a different pattern? A qualified
Yes.
There
are some published graphs that show only increasing or only decreasing
curves. On closer inspection, you’ll see
that only part of the muscle’s contraction was tested, either due to a
limitation of the device or for safety.
Rumor had it that Sergio Oliva, one of the legendary bodybuilders from
the ‘60s and ‘70s, had biceps and forearms so big that they collided halfway
through a curl, preventing his biceps from contracting further. In his case, the Muscle Torque curve for
biceps appeared to only increase, because the size of his muscles interfered
with “normal” limb movement, effectively testing only part of the muscle
action.
Right. Like we all have to worry about that one.
Passive
Tension, Speed of Contraction, and Torque Curves
There are other legitimate reasons for
graphs to depict other than the increase/decrease model. One is “passive tension”. The increase/decrease is created by voluntary
contractions. When an external force
stretches a muscle to near its limit, the active tension contributes less, and
structural components provide more “passive tension” until it breaks5. Technically, there’s greater potential muscle
force available, but obviously there’s no point in trying to load it with
weights.
The
speed of the contraction also affects the shape of the curve6. Different speeds create Maximum Muscle Torque
at different points; it still falls somewhere between least and most
concentric. In the gym, the speed of
contraction is important, but not so much for its effect on the shape of the
curve. In the Resistance Torque chapter,
we discussed that if you heave or drop the weight, you add momentum and
acceleration, and so lose control of Resistance Torque. That aside, the faster a muscle contracts,
the less force it generates; the slower the contraction, the more force7. If you have the technology that eliminates
the effect on resistance, you may be tempted to train with faster contractions;
but you still have to be careful of the muscle yanking on your own joints
during the exercise.
For
most, especially those using weights, the slower contraction allows you to use
more of your potential muscle force. And
at some point in training, you have to use a high percentage of that potential
(if not a maximal effort). Otherwise,
your body would have no reason to maintain or increase your capacity to
generate that force; which means less muscle mass and tone. Your body would perceive the exercise just as
an “activity of daily living” and not change as a result of it.
That
change is represented in Figure 2.4B.
Two curves are shown, one flatter, one more peaked. The flatter represents untrained muscle. The Moment Arm changes are present, the
filaments behave as expected, so there is a slight increase/decrease. The peaked curve represents potential Muscle
Torque after an unspecified amount of ideal training. As the training worked and the fibers grew
larger, the muscle would generate more torque overall, but more so in the middle. Why?
Because the “weakness” at the ends is from the reduced Moment Arms and
positioning of the filaments; not from the size of the fibers. It’s mechanical, not muscular. Regardless of the fiber size, there will always
be optimal overlap in the middle of the contraction, not the ends; and the
Muscle Moment Arms will always be larger in the middle than at full stretch or
contraction. It couldn’t be otherwise,
given the sliding filament and moment arm models.
Back
to the Gym
Wait a minute, you’re thinking. That may be a nice theory, but when I do a
Barbell Curl, I feel pretty weak in the middle, and pretty strong at the start
and finish. My biceps torque curve must
be U shaped. When I bench press, I feel
weak at the bottom and strong at lockout, so my pecs get stronger as they
contract; their torque must “only increase”.
When I row, I feel strong at the start but weaker as the weight comes to
me; my lats’ torque must “only decrease”.
To
explain these apparent discrepancies, we look at the interface: the overlap of
Resistance and Muscle Torque.
Notes
1. Vogel, Prime
Mover, 2001.
2. “The Muscle
side is confusing…” See Harman, 1994, pp 31-34; Brunnstrom’s, 1996, pp 136-146;
Nordin and Frankel, Basic Biomechanics…, 2001, pp 160-165; Levangie and Norkin,
2001, pp95-103.
3. “The muscle
moment arm…” See Harman, pp 28-30; Brunnstrom’s, pp 61-63.
4. All the
previous references cover sliding filament and all the material on muscle
function. The explanation here is based
on Vogel, Prime Mover, pp 12-18.
5. Passive
Tension: Nordin and Frankel, pp 160-161;
Brunnstrom’s, pp 138-140.
6. “The speed at
which it contracts…” See Harman, p 33 for graphs.
7. “…the faster a
muscle contracts…” See Brunnstrom’s, p 142; Nordin and Frankel, pp 158-162;
Levangie and Norkin, pp 97-98.
To order the complete Moment Arm Exercise spiral bound manual, email optimalexercise@comcast.com with the subject line "MAEX". I will send you an invoice via Paypal and ship on payment.
Congruent Exercise:
How to Make Weight Training Easier on Your Joints, is available at Amazon in both print and Kindle format.
