Paradoxical Role of Muscle
During Controlled Movements
D. Gordon E. Robertson, Ph.D.
Yves D. Fortin, M.Sc.
Jean-Marie J. Wilson, M.Sc.
Dan T. Curry, M.Sc.
School of Human Kinetics,
University of Ottawa, Ottawa, CANADA
Supported by the University of Ottawa Rector’s Fund and
Sport Canada Applied Research Fund
Introduction
Anatomically muscle function is determined by
examining how a muscle acts at a single joint
during unloaded movements. For a biarticular
muscle one joint is fixed while its function is
determined at the other joint. The process is
then repeated by reversing the fixation.
Introduction Cont’d
Unfortunately, this method cannot consider how
muscles function when several joints are
moving simultaneously and how function is
influenced by external loads and constraints.
One scheme classifies muscle as either agonist,
antagonist or stabilizer.
Paradoxical Role of Muscle
Molbech suggested that biarticular muscle can act
paradoxically during “controlled” or constrained
movements. That is, when a limb is constrained at
one or both ends, a flexor can produce extension or
an extensor can produce flexion.
This differs from Lombard’s paradox which considers
doubly biarticular muscles at hip and knee during
extension. Extension is explained by differential
moment arms at knee and hip.
Molbech’s Model
• A and K are hinges
AX = AY
Y
K
X
A
Molbech’s Model
• A and K are hinges
• H is constrained to Y-axis
AX = AY = AK + KH
Y
H
K
X
A
Molbech’s Model
• A and K are hinges
• H is constrained to Y-axis
• O is a muscle origin
AX = AY = AK + KH
Y
H
O
K
X
A
Molbech’s Model
•
•
•
•
A and K are hinges
H is constrained to Y-axis
O is a muscle origin
extend line AK to P on arc
of length AK+KH (limb
length)
AP = AK + KH
Y
P
H
O
K
X
A
Molbech’s Model
•
•
•
•
A and K are hinges
H is constrained to Y-axis
O is a muscle origin
extend line AK to P on arc
of length AK+KH (limb
length)
• draw ray L from P
through O
AP = AK + KH
Y
P
H
O
K
X
A
L
Molbech’s Model
•
•
•
•
A and K are hinges
H is constrained to Y-axis
O is a muscle origin
extend line AK to P on arc
of length AK+KH (limb
length)
• draw ray L from P
through O
• if ray OG is above L
muscle causes extension
AP = AK + KH
Y
P
H
O
K
X
A
G
L
Molbech’s Model
•
•
•
•
A and K are hinges
H is constrained to Y-axis
O is a muscle origin
extend line AK to P on arc
of length AK+KH (limb
length)
• draw ray L from P
through O
• if ray OG is below L
muscle causes flexion
AP = AK + KH
Y
P
H
O
K
X
G L
A
Molbech’s Model
•
•
•
•
A and K are hinges
H is constrained to Y-axis
O is a muscle origin
extend line AK to P on arc
of length AK+KH (limb
length)
• draw ray L from P
through O
• if ray OG is along L
muscle acts isometrically
AP = AK + KH
Y
P
H
O
G
K
X
A
L
Paradoxical Muscle Activity?
• what factors characterize paradoxical
activity?
• how are muscle contributions
determined?
• no means of directly measuring
multiple muscle forces, simultaneously
and in vivo
Classification of Muscle
Functions
Muscle functions as: agonist, antagonist, stabilizer,
extraneous or paradoxical.
Function is characterized by:
• its anatomical function (flexor, extensor, . . .)
• the joint’s kinematics (flexion, extension, . . .)
• the joint’s kinetics (moment of force)
• its activity level (EMG above a threshold)
• its kinematics (lengthening or concentric, shortening or
eccentric, static or isometric)
Rectus Femoris during Hip Flexion
in Soccer Kicking
• hip flexor and knee
extensor
• hip flexing
• hip flexor moment
• active contraction
• concentric,
shortening
Classified:
concentric agonist
Gluteals during Hip Extension
in Hurdling
•
•
•
•
•
hip extensor
hip extending
extensor moment
active contraction
concentric,
shortening
Classified:
concentric agonist
Erector Spinae while Stooped
at Waist
• trunk extensor
• trunk statically
extended
• extensor moment
• active
co/contraction
• isometric
Classified:
isometric agonist
Assumptions
It was assumed that, in skilled
athletes, muscles were only
recruited if they were beneficial to
the movement.
Extraneous or inappropriate
contractions and cocontractions
were assumed to be nonexistent.
Classification of Muscle
Function as Paradoxical
To determine paradoxical activity the
following must occur:
• joint motion must be opposite to muscle’s
anatomical function
• net moment of force at the joint must be
opposite to anatomical function
• muscle must be active
• muscle must be shortening
Methods - Joint Kinematics
The joint motion must be opposite to
the accepted anatomical role of the
muscle.
For example, for the biarticular hip
flexor, rectus femoris, to act
paradoxically at the hip then the hip
must be extending.
Methods - Joint Kinetics
The moment of force at a joint must be
opposite to the usual anatomical role of the
muscle.
For example, the moment of force at the knee
must be extensor for a knee flexor, such as,
a hamstring or gastrocnemius muscle, to be
considered paradoxical.
Methods - Muscle Activity (EMG)
The muscle must be actively contracting.
• criterion for significant muscle activity was:
muscle EMG level was >25% EMGMVC (i.e.,
during a maximal voluntary contraction,
MVC)
• EMG level of less than 25% EMGMVC was
considered too low for the muscle to
contribute significantly to the movement
Methods - Muscle Kinematics
The muscle must be contracting
concentrically, that is, it must be
shortening.
An isometric or an eccentric
contraction of the muscle would imply
a stabilizing or antagonist function.
Purpose - Squat Lift
The purpose of this study
was to determine the
functional role of eight leg
muscles, four of which are
biarticular, during knee
extension of loaded and
unloaded squat lifting.
Squat Lift
•
•
•
•
•
six experienced male weight-lifters
cinefilm at 50 frames/second
Kistler force platform
80% maximum lift and no load conditions
EMGs from muscles: rectus femoris,
gluteus maximus, biceps femoris,
semitendinosus, vastus lateralis,
gastrocnemius, tibialis anterior and soleus
• muscle lengths from Frigo’s and Pedotti’s
model with modifications by Hubley
Conclusions - Squat Lift
• biarticular muscles acted as stabilizers
of knee
• no paradoxical activity was performed
• prime movers were the monoarticular
muscles
• knee muscles were responsible for
starting the descent and preventing
hyperextension at the end of the lift
Purpose - Ergometer Rowing
• The purpose of this study was to
determine the functional role of six leg
muscles, three of which are
biarticular, during drive phase of
ergometer rowing.
Experimental Set-up
Strain gauge force transducer
Gjessing
ergometer
Flywheel
Workload
adjustment
Foot
stretcher
Biological
amplifier
Charge
amplifier
Bridge
amplifier
Kistler force
platform
A/D
converter
Cinecamera
Microcomputer
Methods
• four female and four male elite rowers
performed on the ergometer while
kinematic information was recorded on
cinefilm at 50 frames/second
• workload 25 N (2.6 kp) for females,
30 N (3.1 kp) for males
• ten cycles at 27 strokes/minute
• EMGs from MVCs recorded separately
Methods - Forces
• forces measured by Kistler force
platform angled at 10 degrees
• sampled at 200 Hz
• rotated to Newtonian frame of
reference
• handle forces measured by in-line
force transducer
Methods - Joint Kinetics
• inverse dynamics to compute the net
moments of force produced at the
ankle, knee and hip joints
• powers produced by moments were
computed as product of moment and
joint angular velocity (M . w)
Methods - Electromyography
• muscles investigated were the
monoarticular: vastus lateralis, soleus,
gluteus maximus and the biarticular: biceps
femoris, rectus femoris and gastrocnemius
• sampled simultaneously at 200 Hz for ten
rowing cycles
• CMRR >100 dB, 10-700 Hz filter, 2000 gain
• linear envelope detector (6 Hz cutoff)
• ensemble averaged across entire stroke
Methods - Muscle Length
• instantaneous length of each muscle
was computed from the digitized
image with to adaptation of the
muscle length model of Frigo and
Pedotti (1978)
• model based on marker kinematics
and subject height
Results
To provide higher accuracy, the drive
phase was divided in three equal
parts; each criterion delineated by the
classification scheme was verified for
each muscle during each third of the
drive.
Moment Powers of Male Rowers
1500
Hip
RMBS
RMDH
RMKH
RMNT
RMSD
1000
500
Concentric
0
-500
Eccentric
Knee
1000
500
Concentric
0
-500
Eccentric
500
Ankle
Concentric
0
Eccentric
-500
0
10
20
30
40
50
60
Time (% drive)
70
80
90
100
Moment Powers of Female Rowers
1500
Hip
RFEK
RFLM
RFLN
RFMM
1000
500
Concentric
0
-500
Eccentric
Knee
1000
500
Concentric
0
-500
Eccentric
500
Ankle
Concentric
0
Eccentric
-500
0
10
20
30
40
50
Time (% drive)
60
70
80
90
100
Results - Knee
• angular velocity curve portrays relatively
slow joint motion (below 4 rad/s)
• knee moment was extensor for 2/4 females
and all males
• weak moment for females (>100 N.m) but
strong for males (>150 N.m)
• moment produced positive work for all
males during middle and late drive and for
two females during middle drive
Results - Knee Kinetics
Figure is from a male subject and
depicts the knee’s angular
velocity, net joint moment of force
and the power produced by the
moment of force.
Results - EMG
• EMG curves show that most muscles
contracted in-phase with each other
• most were significantly active
(EMGmax >25% EMGMVC) during
middle and late third of drive
• most were below threshold during
first third of drive (i.e., end of
recovery)
Results - Muscle Shortening
• muscle velocities were time
normalized to the drive duration
• positive velocity indicated shortening
or concentric contraction (same
convention as muscle physiologists)
• negative velocity indicated
lengthening or eccentric contraction
Discussion - Classification
• biceps femoris acted paradoxically for
knee extension in one female and two
males
• gastrocnemius acted paradoxically for
knee extension in one female and two
males
• rectus femoris acted paradoxically for
hip extension in three of four males and
three of four females during late drive
Discussion - Powers
• female rowers produced majority of
work by hip extensors; knee and ankle
extensors produced insignificant
amounts of work or negative work
• male rowers had contributions from
ankle, knee and hip extensors; mainly
from hip
Conclusions - Rowing
Paradoxical activity was detected
infrequently during knee extension by
the biarticular biceps femoris and
gastrocnemius.
More intriguing was the detection of
paradoxical activity from the action of
rectus femoris during hip extension.
References
Carlsoo, S. 1966 Acta Morphologica Neerlando-Scandinavica,
6:377-386
Elftman, H. 1939 American Journal of Physiology, 125:357-366
Frigo, C & Pedotti, A. 1978 Biomechanics IV, 355-360
Lombard, WP. 1903 American Physical Education Review, 8:141145
Molbech, S. 1965 Acta Morphologica Neerlando-Scandinavica,
6:171-178
Rasch, PJ & Burke, RK. 1978 Kinesiology and Applied Anatomy,
6th edition
Questions?
Answers?
Thank you.
Pectoralis major during horizontal flexion
in tennis forehand stroke
• horizontal flexor
• horizontal flexing
• horizontal flexor
• active contraction
• shortening
Classified:
concentric agonist
Anterior deltoids during arm stand
in gymnastics
• shoulder flexor
• shoulder statically
extended
• extensor moment
• active
cocontraction
• isometric
Classified:
stabilizer
Hamstrings during knee extension
in running
•
•
•
•
•
knee flexor
knee extending
flexor moment
active contraction
eccentric,
lengthening
Classified:
eccentric agonist
Neck extensors during
keyboarding
• neck extensor
• neck statically
flexed
• extensor moment
• active contraction
• isometric
Classified:
isometric agonist
Rectus abdominis during trunk flexion
in high jumping
•
•
•
•
•
trunk flexor
trunk flexing
flexor moment
active contraction
concentric,
shortening
Classified:
concentric agonist
Vastus lateralis during knee flexion
in soccer kicking
•
•
•
•
•
knee extensor
knee flexing
extensor moment
active contraction
eccentric,
lengthening
Classified:
eccentric agonist