View Full Version : Force and accuracy

Force Health Group
05-17-1995, 12:59 PM
Some time ago I floated a query re accuracy/control of movement at different
percentages of maximal strength. I received many responses, and would like
to offer a belated thanks to all those who responded. A summary of the
responses follows.

Thanks to everyone who responded.

Dave Hewson
Aviation Medicine Unit
RNZAF Base Auckland
Private Bag Whenuapai

Phone: 64-9-416-3337
Fax: 64-9-416-3338
E-mail: d.hewson@forchlth.army.mil.nz

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Kathy Myburgh, KATHYMYB@physio.uct.ac.za

I am a gymnastics fan and think that large amounts of force can be
produced with large amounts of accuracy - no scientific evidence
though. The crucial thing is to "train" specifically at the forces
you expect will be necessary and to then require skill at that force
output - the skill/fine tuning will come with repetition. Pre-empting
is important ie know the outcome desired and know how it should feel
if it was going to be successful. For emergency situations, there
will be less control. BUT the better the gymnast the better he/she
can control an emergency despite working at higher force outputs than

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Jeff Ives, jives@camel.campbell.edu

You also may wish to look at the literature on strength and
speed of movement, especially under conditions of added weight.
For example, some old refs:
Smith, LE (1961). Res. Quart. 32:208-220.
Smith, LE and JD Whitley. (1965). Arch. Phys. Med. Rehab. 46:772-777.
Smith, LE and JD Whitley (1963). Res. Quart. 34:489-596.
Lagasse, PP. (1979). Perc. Mot. Skills. 49:151-161, 1979.
Whitley and Smith (1963). Res. Quart. 34:379-395.
Clarke, DH. (1960). Res. Quart. 31:570-574.
Henry, FM and Whitley. (1960). Res. Quart. 31:24-33.
Nelson, RC and RA Fahrney. (1965). Res. Quart. 36:455-463.
Also try the rapid movement (eg. triphasic pattern) literature
with inertial laads, e.g.,
Schmidt et al. (1979). Psych. Rev. 86:415-451, 1979.
Sherwood et al.(1988) J. Mot. Beh.20:106-116.
Sherwood et al(1988) Exp. Brain Res. 69:355-367.

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Assim G. Chowdhary, CHOWDHAG@sportex.bham.ac.uk

Might want to look at coactivation of agonist / antagonist, and
modulation of stiffness (effective rather than real energy absorbing
releasing spring stuff).

Multiple Muscle Systems , J.M. Winters & S. Woo, 1990 (pub.
Springer Verlag) has some excellent stuff in it.

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Kenneth Graham, kgraham@magna.com.au

One author you may wish to search on through Medline is D.I.McCloskey. Ian
is a Professor at the University of New South Wales (Sydney Australia)
and is a frontline researcher in proprioception. Another person who is also
in this area is Simon Gandevia.

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Gary Kamen, KAMEN@enga.bu.edu

I was interested in your concern regarding accuracy at high force levels.
I currently conduct research in human motor unit behavior and have measured
motor unit firing rates at high force levels in young and older individuals,
as well as in older competitive weight lifters. I haven't been as
concerned (until recently) with issues regarding accuracy. But I can
relay a number of issues that may be involved.

As the force increases and the requirement for precision is the same
or increases, it is legitimate to expect additional activity from the
antagonist musculature. While it may seem that this is contrary to one
might expect, the antagonist muscle firing actually helps to maintain
precision through co-contraction. The development of skill is usually
accompanied by greater co-contraction activity. There has been some dis-
cussion that fatigue is accompanied by greater motor unit synchronization,
but this really hasn't been verified in my opinion.

Finally, you might try to use a simulator instrumented to measure some
forces to measure the amount of force involved, particularly under the
stressful conditions you mention. I'm a recreational pilot myself,
and although I suspect the forces involved in flying a Cessna 172 are
less than those of a fighter with hydraulic power loss, I rather think
that the forces we're talking about are not that high.

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Larry Abraham, l.abraham@mail.utexas.edu

Dick Schmidt has published several papers on a force-force variability
relationship which I believe is close to your topic. He reviews this topic
in his text: Motor Control and Learning, published by Human Kinetics.

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Daniel R. Baker, drbaker@u.washington.edu

Check out a Dissertation ('86) and several papers ('88-'89 or '89-90,
can't remember which) by Steve Wiker. Not on maximal movements, but good
reference lists.

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Clayton Gable, ptycg@ttuhsc.edu

My dissertation work was on learning using a summary knowledge of results
paradigm. Not very related to your query but my task was one of isometric
force production with the triceps brachii. Do you have some particular
questions about force production accuracy? Also, that same force production
task has been used on several project in Charles H. Shea's lab.

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Mark D. Grabiner, grabiner@bme.ri.ccf.org

We've been studying the ability to control isokinetic contractions, both
eccentric and concentric, as a function of isokinetic velocity and level of
required force. Not surprisingly, our data (measured on trunk, knee, and
ankle musculature) has been consistent with the motor control literature
reporting that the error in control increases as a function of the
level of force of isometric contractions. One of the things I have found
to be quite interesting are the differences between the ability to control
concentric and eccentric contractions. In normal controls there is not
typically what I would call meaningful differences but in the elderly and
in subjects with joint-specific pathologies the ability to control
eccentric contractions appear to become compromised.

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Barry Wilson, bwilson@pooka.otago.ac.nz

For theoretical support for your argument, look at the force/velocity and
length/tension curves at different percentages of max effort. Slopes are
greater at maximal efforts cf lesser efforts implying greater changes in
force output for a given change in muscle length at maximal efforts cf
lesser efforts ie sensitivity of force output for a change in muscle length
changes for different efforts.

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Normand Teasdale, Normand.Teasdale@pmh.ulaval.ca

Several authors have addressed this issue in the motor control literature.
This list of reference is certainly not exhaustive but should give you a start.
Good readings:

Schmidt RA, Zelaznick HN, Hawkins B, Frank JS, Quinn JT. Motor-output
variability: A theory for the accuracy of rapid motor acts. Psychol Res

Schmidt RA, Sherwood DE. An inverted-U relation between spatial error and
force requirements in rapid limb movements: Further evidence for the
impulse variability model. J Mot Beh 1982;8:158-70.

Schmidt RA, Sherwood DE, Zelaznik HN, Leikind B. Speed-accuracy trade-offs
in motor behavior: Theories of impulse variability. In: Heuer H, Kleinbeck
U, Schmidt KH, eds. Motor behavior: Programming,control, and acquisition.
Springer-Verlag ed. Berlin:, 1985:79-123.

Newell KM, Carlton LG, Hancock PA. Kinetic analysis of response
variability. Psychol Bull 1984;96:133-51.

Kim S, Carlton LG, Newell KM. Preload and isometric force variability. J
Mot Beh 1990;22:177-91.

Meyer DE, Smith JEK, Wrigth CE. Models for the speeed and accuracy of
aimed movements. Psychol Rev 1982;89(5):449-82.

Meyer DE, Abrams RA, Kornblum S, Wright CE, Smith JEK. Optimality in human
motor performance: Ideal control of rapid aimed movements. Psychol Rev

Ghez C, Gordon J. Trajectory control in targeted force impulses. I. Role
of opposing muscles. Exp Brain Res 1987;67:225-40.

Gordon J, Ghez C. Trajectory control in targeted force impulses. II. Pulse
height control. Exp Brain Res 1987;67:241-52.

Gordon J, Ghez C. Trajectory control in targeted force impulses. III.
Compensatory adjustments for initial errors. Exp Brain Res 1987;67(253-

Teasdale N, Forget R, Bard C, Paillard J, Fleury M, Lamarre Y. The role of
proprioceptive information for the production of isometric forces and for
handwriting tasks. Acta Psychol (Amst) 1993;82:179-91.

Stelmach GE, Worringham CJ. The preparation and production of isometric
forces in Parkinson's disease. Neuropsychologia 1988;26:93-103.

Stelmach GE, Teasdale N, Phillips J, Worringham CJ. Force production
characteristics in Parkinson's disease. Exp Brain Res 1989;76:165-72.

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Carolee Winstein, winstein@hsc.usc.edu

You should look at several papers by Schmidt et al dealing with motor output
variability--Schmidt, Zelaznik, Hawkins, Frank and Wuinn (1979) Psych rev,
86, 415-451; Schmidt, Sherwood, Zelaznik & Leikind--"Speed-accuracy
trade-offs in
motor behavior: theories of impulse variability, 1985, chapter in Motor
H. Heuer, U. Kleinbeck, and K.-H. Schmidt (Eds), Springer-Verlag, Berlin. Also,
Sherwood & Schmidt (1980), The relationship between force and force
variability in
minimal and near-maximal static and dynamic contractions. Journal of Motor
Behavior, 12, 75-89.

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Bob Banks, Bob_Banks@gatormail.dciem.dnd.ca

There is no ready reference for this problem that I am aware of. However,
there is an interesting aspect that you may be interested in. Our Canadian
Forces aerobatic team, the "Snowbirds" use full nose-down trim during their
air demonstrations that involve nine-plane tight formations with up to eight
feet of wing overlap. With full nose-down trim, at approx 250 knots, the
pilot is required to exert around 35 lbs aft stick force to maintain level
flight, and proportionally more or less to follow the flight maneuvers. This
is maintained for up to 25 minutes. The pilots believe that full nose-down
trim is an absolute necessity for precision flight. Having said that, the
biggest complaint, especially early in the season, is muscle fatigue, and
many team candidates are rejected because of lack of muscular strength.
Weight training is commonly undertaken by candidates hoping to make the team.

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Wynne Lee, wlee@casbah.acns.nwu.edu

There's a large body of literature (recent and back into the 70's) in the
ergonomics & psychology literature on the relationship between force and
force variability in a variety of simple isometric and more complex
movement tasks. Some names to start with are Newell, Myers, Schmidt, Wing.
I'd also guess that the older (40's-50's-60's) literature on human
performance that emerged from WWII would address some of those questions.
Some names there are Poulton, Welford -- a lot on tracking and joystick

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Jim Frank, frank@healthy.uwaterloo.ca

There is a good amount of information on this which started
with research by myself, Howie Zelaznik and Dick Schmidt some 15 years
ago. You should consult Schmidt et al (1979). Motion Output
Variability: A Theory for the Accuracy of Rapid Motor Acts.
Psychological Review, 86: 415-451.

Carlton and Newell (1988). Force Variability and Movement Accuracy in
Space-Time. Journal of Experimental Psychology: Human Perception and
Performance. 14: 24-36.

Newell and Carlton (1988). Force Variability in Isometric Responses. J.
Exp. Psychol: Human Percep Perf. 14: 37-44.

Ulrich and Wing (1991). A Recruitment Theory of Force-Time Relations in
the Production of Brief Force Pulses: The Parallel Force Unit Model.
Psychol. Review. 98: 268-294.