The role of weightbeari ng and non-weightbearing muscles 9 5
VM RF VL
--------'\-VI
SR---,�
ADL---\-�
GR
(b)
Figu re 6.2 (a) Resisted knee extension in sitti ng. (b) Mag netic resona nce images depicti ng quadriceps pattern of use
during (a). AD B, adductus brevis; AD L, adductus longus; AD M, adductus mag nus ; BF, biceps femoris; GR, g racil is; RF,
rectus femoris; SR, sartorius; ST, semitendi nosus; VM, vastus medialis; VL, vastus latera l is; VI, vastus intermed ius.
(Reproduced w ith permission of Tesch 1 993, p. 47.)
safe loaded weightbearing. Such joint protection is
determined by the muscle recruitment patterns at
each joint of the limb opposing gravitational force.
As far as the global muscles are concerned, it will
be argued that it is predominantly the one-joint
(or one area of the spine) extensors of the trunk
and limbs that are the weightbearing muscles,
providing the mechanical support and joint pro
tection for functional loaded postures (see Fig.
6.1b) and that these muscles are closely linked to
the function of the local muscle system. The multi
joint muscles, which have multiple functions in
relation to joint movement, do not, in normal erect
working postures, have a weightbearing role (i.e.
they are non-weightbearing muscles).
This concept will be developed using the muscles
and joints of the lower limb as the model. The role
of the muscles of the upper quadrant in antigravity
weightbearing function, and their links to weight
transfer through the trunk, is a topic for our on
going research into weightbearing mechanisms
and joint protection.
Recruitment patterns of synergists in
open chain exercise loading
Before describing a differential function for one
joint and multijoint muscles, it is first important to
recognize that in most loaded exercise situations,
both one-joint and multijoint synergists are
recruited together to provide the force to oppose the
external resistance. For example, resisted knee
extension in sitting (Fig. 6.2a) requires the recruit
ment of all of the quadriceps muscles, including the
one-joint vasti and the multijoint vastus medialis
oblique. This is illustrated schematically in the
functional magnetic resonance images (MRI) by
Tesch (1993) depicting high muscle use (white),
]
9 6 T H E J O I NT P ROTECTI O N M EC H A N I S M S
medium muscle use (grey) and lack o f use (black).
These MRI images, which are taken before and after
a loaded knee extension exercise, demonstrate the
pattern of use of the muscles. Figure 6.2b demon
strates the high use (white) of all quadriceps syner
gists during the exercise. Also important to note is
the lack of use (black) of the mutijoint hamstring
muscles (antagonists) as well as lack of use of all the
adductors muscles of the hip. Consequently, exer
cise to increasing strength, power and endurance of
muscles around a single joint by traditional means
involves the use of all muscles in the movement
direction of the force, with relaxation of the main
antagonist set of muscles. It is likely that such exer
cise in this example does not include the adductor
muscles (Fig. 6.2b). Therefore, it could be argued
that reduced function of the adductor magnus,
which functions as an extensor of the hip in weight
bearing (reviewed by Hodges and Richardson 1993)
could, over a period of time, result in reduced pelvic
stabilization for weightbearing.
Recruitment patterns of synergists in closed
chain exercise loading
Completely different recruitment patterns of the
one-joint and multijoint muscle synergists of the
quadriceps occur in closed chain loading. Closed
chain loading involves joint compression, with
proximal and distal segments moving together to
load longitudinally through the body including
through the feet.
Compared with open chain loading, closed
chain exercise loading highlights the differential
function of the one- and multijoint muscles, with
the one-joint muscles recruited optimally to
oppose external resistance. For example, resisted
knee extension in lying (closed chain) (Fig. 6.3a)
requires the recruitment of all of the one-joint vasti
muscles but does not use the multijoint rectus
femoris. This is illustrated schematically in the
functional MRI illustrations by Tesch (1993)
depicting quadriceps level of use after a loaded,
closed chain knee extension exercise in the form
of the leg press. Figure 6.3b demonstrates the high
use (white) of the vasti synergists during the exer
cise. Most importantly, there'is lack of use (black)
of the multijoint hamstring muscles as well as the
multijoint hip muscles (e.g. sartorius). This type of
(a)
,---'-;',;-----+--Vl
SR---,�
ADL--\-....
GR
ADM ST BF
(b)
Figure 6.3 (a) Closed chain resisted knee extension.
(b) MRI depicting quadriceps pattern of use during (a). AD
B, adductus brevis; AD L, adductus longus; AD M, adductus
mag nus; BF, biceps femoris; GR, g racil is; RF, rectus femoris;
SR, sartorius; ST, sem itendi nosus; VM, vastus medialis;
VL, vastus lateralis; VI, vastus intermed ius. (Reproduced
with permission of Tesch 1 993, p. 59.)
exercise is also well suited to recruitment of the
large one-joint adductor muscles of the hip (e.g.
adductor magnus and brevis).
A more functional closed chain exercise would
be a 'squat' or 'lunge' exercise. Importantly, the
(b)
Figure 6.4 (a) Lunge exercise. (b) MRI depicting
quadriceps pattern of use during (a). AD B, adductus
brevis; AD L, adductus longus; AD M, adductus mag nus;
BF, biceps femoris; GR, g racil is; RF, rectus femoris;
5R, sa rtorius; 5T, sem itend i nosus; VM, vastus med i a l is;
VL, vastus lateral is; VI, vastus intermed ius. (Reproduced
with permission of Tesch 1 993, p. 46.)
The role of weightbearing and non-weightbearing muscles 9 7
Q
00000 = Local muscles
"VV"V'V"V'. = One joint muscles
= Multiple joint muscles
Figure 6.5 The one joint muscles a re stretched
under the force of g ravity in weightbea ri ng, w h i l e
t h e multijoint muscles a re more l i kely t o b e i n a more
shortened (relaxed) position.
lunge exercise with shoulder load (Fig. 6.4a) has
the same muscle recruitment patterns (Fig. 6.4b) as
the leg press (Fig. 6.3b; Tesch 1 993).
However, although squat and lunge exercise per
formed in the erect posture are more functional
than the leg press, it should be recognized that these
exercises also include the balance and sway aspects
of antigravity, upright posture function, and it may
be more difficult to control the joint loading and
levels of individual antigravity muscle recruitment
for treatments. This aspect of progressive exercise
will be discussed in detail in Chapter 15.
Increasing strength, power and endurance of
muscles involving several joints in the kinetic chain
in closed chain exercise involves a different set of
muscle synergists. From a biomechanical point of
view, some muscles (i.e. the one-joint muscles) are
stretched under the force of gravity in weightbear
ing (i.e. closed chain) activities (Fig. 6.5), while the
non-weightbearing, multijoint muscles are more
likely to be placed in a more shortened relaxed
position, as while they are stretched over one joint,
they are relaxed over another (Fig. 6.5).
Consequently, it can be argued that the anti
gravity (one-joint) muscles, which are under
stretch (tend to lengthen) with gravity load, are
OJ
9 8 T H E J O I NT P ROTECTI O N M EC H A NI S M S
providing joint protection and support in the erect
working or loaded posture. These muscles would
also be importan t for the transfer of load in this
position.
There is some initial evidence that the local
muscles and one-joint muscles are closely linked
together in antigravity function. An EMG study of
Hodges and Richardson (1993) demonstrated that
co-activation of adductor magnus (one-joint hip
muscle) and vastus medialis oblique (a local muscle
of the knee) was significantly higher in weight
bearing than in non-weightbearing situations. This
study also suggested that a strong link may exist
between weightbearing function of the muscles of
the hip and the knee joints.
Closed chain exercise involving the trunk and
upper limbs is likely to present the same pattern of
activation that is observed for the trunk and lower
limbs (i.e. recruitment of the one-joint antigravity
muscles with relaxation of the multijoint muscles).
In an MRI assessment of the three heads of the tri
ceps brachii during overhead (antigravity) upper
limb extension with heavy weights, Tesch (1993)
reported that there was maximal recruitment of
the one-joint heads of the muscle, with relaxation
of the multijoint head of the muscle (Fig. 6.6).
Future research into the possible relaxation of the
latissimus dorsi and pectoralis muscle during this
type of closed chain exercise for the trunk and
upper limbs may prove useful in establishing the
Figure 6.6 Antig ravity upper l i m b extension with heavy
weig hts.
joint protective mechanisms of the lumbopelvic
region as well as being useful in the prevention
(and treatment) of many shoulder pathologies.
Although the antigravity (one-joint) muscles are
recruited in closed chain activity, there is evidence
that these muscles providing joint protection and
support are not used in some non-weightbearing
conditions, for example where body weight is
minimized and increasing speed is used to increase
the level of muscle contraction for training.
Recruitment patterns of synergists in fast
ballistic, open chain exercise
Interaction of the one-joint and multijoint syner
gists with open chain, ball istic movement (speed
loading) results in recruitment patterns that are
the direct antithesis to the patterns seen in closed
chain loading conditions. That is, this pattern of
exercise favours the multijoint muscles, with the
antigravity one-joint muscles not responding.
Some of the first evidence for this differential
function of one-joint and multijoint muscles came
from research involving fast ballistic flexion/
extension movements of the knee, involving the
quadricep and hamstring muscle groups.
Richardson and Bullock (1986) studied subjects
performing knee flexion / extension movements in
a prone position at progressive increases in speed
and with individual muscle recruitment measured
with surface EMG. A spring was attached to the
ankle at a set angle (Fig. 6.7) to deload the lower
Figure 6.7 The exercise model with a spring
attach ment to reduce the load of the lower leg
to zero during the hig h-speed bal l istic task.
leg and minimize the effect of gravity during the
movement. Biomechanical analysis showed how
the spring negated the leg load. The movement
model, which involved ballistic movement with
no time for sensory feedback, was considered
to be a largely preprogrammed action (Desmedt
and Godaux 1978) and, therefore, operated under
'open loop' motor control conditions. In ballistic
movement conditions where the gravitational
load cues had been eliminated, recruitment of the
fJ.VS 80
70
60
50
40
30
20
10
o
o Speed: Slow
• Speed: Natural
" Speed: Fast
Vastus lateralis Rectus femoris Vastis medialis Lateral hamstring
Fi gu re 6.8 Electromyographic activity measured over
three movement cycles with the ballistic exercise. Note
the relative increase in activity of the rectus femoris and
hamstrings (multijoint muscles). (Reproduced with
permission from Richardson and Bul lock 1986, p. 55.)
AD B = Adductor brevis
AD L = Adductor l ongus
AD M = Adductor magnus
BF = Biceps femoris
GR = Gracilis
RF = Rectus femoris
SR = Sartorius
ST = Semitendinosis
VM = Vastus medialis
VL = Vastus lateralis
VI = Vastus intermedius
Stand, look down at your right leg,
and imagine l ooking into a slice
(cross-section) of your right thigh.
SR-+--
ADL ---'\--�---'
GR
ADM ST
The role of weightbearing and non-weightbearing muscles 99
multijoint rectus fem9ris and hamstrings increased
significantly with increasing speeds while the
recruitment of the one-joint vastus lateralis and
the local muscle vastus medialis oblique was not
affected (Fig. 6.8). This is demonstrated schema ti
cally in Figure 6.9.
Most importantly, the local muscle vastus medi
alis oblique was recruited tonically in 90% of sub
jects during the high-speed phasic movement,
indicating that it was not involved in lower leg
movement when gravitational load cues were
eliminated . Interestingly, vastus lateralis was also
recruited tonically in 40% of subjects. These results
provide some evidence that both the l ocal muscle
vastus medialis oblique and the one-joint muscle
vastus lateralis do not respond to movement cues
given through fast ballistic knee movement. This
may indicate that these synergists are recruited
together, as proposed earlier in this chapter, for the
antithesis of this exercise movement: the antigrav
ity, weightbearing function.
Following this knee muscle research, Ng and
Richardson (1990) studied the effect on the func
tion of the lower leg muscles of a 6-week exercise
programme involving rapid (ballistic) ankle plantar
flexion. While jumping height improved, the iso
metric strength of the soleus was significantly
VI
ADB
BF
Figure 6.9 The high
use of the multijoint
muscles and low use
of the one joint
muscles during non
weightbearing bal listic
exercise, adapted from
the model used by
Tesch.
]
100 T H E J O I NT P ROTECTI O N M EC H A N I S M S
Table 6.1 Summary of Rood's approach to the differentiation of muscle
Muscles active in patterns of functional
mobi lity (mobil izers)
Muscles active in patterns of
funct ional stabi lity (stabil izers)
Exa mple muscles
Fibre type
Multiarthroda l muscles, flexors, adductors (vasti)
Fusiform, fibres para l lel to the long axis
One-joint extensors and abductors
Bipennate (fan shaped or irregular),
fibres run obliquely
More superficia l (and more lateral)Location
Relationship to joint
Activity
Muscle fibres further from the joint on which they act
More active when distal lever is free and
Located deeply and more medial
Fibres cross one major joint
Function in heavy work, associated
with joint compression as in
weightbea ring
non-weig htbea ring
Leverage More active in l ight work of sma l ler lever acting on
the larger one, in skill activities
More active in movement of heavier
larger object while lighter lever is fixed
Capable of prolonged holding especia l ly
in a stretched position (tonic,
continuous activity)
Active period Work to initiate movement and perform bursts of
activity (phasic)
Threshold of stimulation
Motor units affected
From Stockmeyer 1967.
Low
Mainly quick acting
reduced. Therefore, rapid movement favoured
recruitment of the multijoint gastrocnemius, with
decreased use of the one-joint muscle soleus. This
research is in line with the argument that repeti
tive rapid movement is more likely to recruit pre
dominately the multijoint muscles.
Of interest, this type of speed loading, espe
cially in non-weightbearing, results in high muscle
activation levels, which are accompanied by joint
distraction rather than joint compression. With
less joint loading involved, this type of exercise
is usually more comfortable for the patients with
joint injury and pain. However, it is important to
consider that this type of exercise loading heavily
favours the multijoint muscles and reduces the
contribution of the one-joint muscles.
A neurophysiological model
Neurophysiologists Desmedt and Godaux (1 978)
contributed significantly to knowledge in this area
of muscle control. They described two types of
voluntary movement. 'Ramp' movements (which
can be fast or slow) are those that are continuously
controlled by sensory input from the periphery,
with motor commands guided by the feedback
High
Mainly slow acting
system. This type of movement is similar to closed
kinetic chain function, which demonstrates a
dominance of the one-joint, weightbearing mus
cles. The antithesis of ramp movement is 'ballistic'
movement, involving largely a preprogrammed
action with minimal possibility of modification
(sensory feedback) because of its rapid nature.
This is demonstrated in the rapid knee flexion/
extension model, which demonstrates a domi
nance of multijoint, non-weightbearing muscles.
Desmedt and Godaux (1978) acknowledged that
these represent the extremes of motor function,
with most functional activities consisting of a
combination of both types of movement.
The differing recruitment patterns of human
weightbearing and non-weightbearing muscles
at the two extremes of function are very similar
to the functional categorization of muscles in
animals. Since the last part of the 19th century, phys
iologists have recognized that 'fast' and 'slow'
muscles exist in animals. Denny-Brown (1929) com
pleted histological studies on various animal mus
cles and came to the conclusion that, as a general
rule, the red slow muscles (which exhibit longer
twitch contraction duration) form the deeper layers
of skeletal muscle, have shorter tendons and consist
The role of weightbearing and non-weightbearing muscles 101
Table 6.2 Muscle recruitment with extremes of exercise conditions
Weightbearing muscles
One-joint muscles (and local muscles)
Separation in extreme closed loop motor function
Exercise: closed chain exercise
Static weightbearing
Antigravity working postures
Joint compression
of units with low threshold for postural reflexes. The
extensors at each joint, as an undifferentiated group,
belong to this type of muscle, except for the double
joint, more superficial extensors, which, together
with all flexor groups, develop as more rapidly con
tracting muscles (i.e. the pale, fast muscles).
Interestingly, it was with these types of study
in mind that Rood (1962) developed her theor
ies on muscle types as a basis for rehabilitation. She
suggested that fast 'mobilizers' (multijoint mus
cles) were made up of fast contracting motor units
and were involved in rapid skilled movements,
while the slow 'stabilizers' (one-joint muscles)
consisting of slow-contracting motor units were
involved in weightbearing stabilizing function. In
1967, Stockmeyer wrote a clinical interpretation of
the Rood approach, which has implications for
treatment and prevention of musculo-skeletal
injuries such as low back pain. This approach is
summarized in Table 6 . 1 .
I t could b e argued from information provided
earlier in this chapter that the ideas of Denny
Brown (1929) and Rood (1962) may be, in many
ways, acceptable today. However, as more recent
studies of muscle fibre types in humans have
established .that, unlike animals, skeletal muscles
consist of a variable 50:50 mixture of fast and slow
twitch muscle fibres, the differences in function of
muscle synergists can only be explained in terms
of differences in motor control rather than fibre
type predominance. This would be an important
area for neurophysiological research on which to
base exercise models.
In summary, the global muscle synergists
(weightbearing and non-weightbearing muscles)
demonstrate differential muscle recruitment
patterns at the extremes of the ramp (closed chain)
Non-weightbearing muscl es
Multijoint/multifunction muscles
Separation in extreme open loop motor function
Exercise: open chain exercise
Rapid, ballistic movement
Eliminate gravity
Joint distraction
and ballistic exercise conditions. Table 6.2 summar
izes the extreme conditions of exercise and the
muscle synergists involved.
THE CONTROL AND CO-ORDINATION OF
ONE-JOINT AND MULTIJOINT MUSCLES
The co-ordination of one-joint and multijoint musles
in the dynamic interaction of body segments
remains an issue of intense debate in the current
motor control literature. Prilutsky (2000) high
lighted the 'spring like' behaviour of multijoint
muscles, and their efficiency in multijoint move
ments in facilitating energy transfer between joints;
he also provided arguments, from an evolutionary
viewpoint, that having only one-joint muscles
would produce inefficient movements.
Bobbert and van Soerst (2000), in a commentary
on Prilutsky's paper, provided more evidence
for the multijoint muscles being considered the
solution to the problems of evolution and increasing
efficiency of movement. They presented arguments
to explain how multijoint muscles are coordinated
to favour their force-velocity relationships to give
an efficient, skilled performance. The problem from
a health science perspective is how the nervous sys
tem deals with the resultant unfavourable length
tension relationships in the one-joint muscles,
which must offer 'directional restraint' to the joints
through all ranges of functional movement. This
would be the most challenging to one-joint muscle
control when they are in their shortened position,
with resultant unfavourable length-tension relation
ships (see eh. 7).
Interestingly, Bobbert and van Soerst (2000)
reflected on the hypothesis of van Ingen Schenau
et al (1994) who suggested that one-joint muscles
102 THE JOINT PROTECTION MECHANISMS
are recruited in high-energy tasks based on spin
dle information in order that these muscles can be
activated in their shortened range. They suggested
that other sensory information relating to move
ment information, including the line of action of
the forces, would be more important for the multi
joint muscles. Chapter 7 lends support to these
theories that one-joint and multijoint muscles can
be separated in terms of reliance on different types
of sensory information, and it goes on to argue
that the one-joint system primarily has a weight
bearing (antigravity) role while the multijoint
system has a non-weightbearing role.
Therefore, although a better movement per
formance would be expected if all muscles were
multijoint, we propose that, for the health field,
the one-joint muscles should be considered the
solution to the problems of evolution, where their
roles in the adjustment of the body segments to an
erect posture (against the forces of gravity) and in
supporting and protecting the weightbearing joints
during functional movement become the most
important issues of motor control, in relation to the
co-ordination of the one- and multijoint muscles.
BASIS FOR AN ANTIGRAVITY
EXERCISE MODEL
The separation of function of non-weightbearing
and weightbearing muscles at the extremes of the
motor control continuum has important implica
tions for rehabilitative and preventative exercise.
Non-weightbearing muscles are facilitated in ballis
tic motor tasks at one extreme of the control model
while weightbearing muscles are facilitated at the
other extreme (i.e. in ramped (closed chain) motor
tasks). This could be how impairments develop
through lack of use of the weightbearing muscles,
and overuse of the non-weightbearing muscles,
when the ballistic motor fw1ction is dominant. This
model could also form the basis of treatment of
overactive non-weightbearing muscles, and under
active weightbearing muscles, as the closed chain
exercise models are likely to facilitate weightbear
ing muscle function and 'turn off' the more active
non-weightbearing muscle system.
It was argued in Chapter 5 that providing joint
stiffness (and muscle stiffness) to the lumbopelvic
region for high-load antigravity ftmction of mus
cles requires very specialized motor control stra
tegies for that region. The second part of the
integration phase, with the local muscles integrat
ing with the global muscles, is gained through
focusing on the close links between the local and
the weightbearing muscles and, therefore, the
muscle corset (Ch. 5) combined with closed chain
exercise for the weightbearing muscles (and which
differentiates weightbearing from non-weight
bearing muscles) would be the rehabilitative and
preventative exercise of choice.
Training and improving the joint protection
mechanisms is based on normal function of the
muscle system for joint protection (Chs 2-6) as
well as on changes that occur in the muscle system
with dysfunction associated with prolonged
deloading (Ch. 7), injury (Ch. 8) and pain (Ch. 9).
This chapter has focused on the functional categor
ization of synergistic muscles, and the various pat
terns of muscle function related to the addition of
load to the joints in exercise. Chapter 7 will deal
with deloading and loss of antigravity function
and how it differentially affects the weightbearing
muscles (including local muscles) in a different
way to the non-weightbearing muscles; this leads
to impairments in the joint protection mechanisms
and to the development of joint injury