Michael Ro
Mon, Aug-12-02, 20:02
Some time ago it was contested on this newsgroup that increase
in muscle force or strength is not necessarily accompanied by
an increase in neural drive or the electrical activity of the
relevant muscles as measured by the EMG. This topic was
addressed in the article below.
This issue is of central importance in all strength training,
because increase in strength classically is recognized to be
the result of:
(a) increased muscle mass (or cross-sectional area),
(b) increased neural drive, or...
(c) a combination of both of the above processes.
The matter of increased neural drive is regarded to be of
special importance during the early stages of training or
retraining (after a prolonged lay-off), because
significant increases in hypertrophy do not usually occur
during such a stage of training, although increases in
strength are very common.
If we examine (a), this suggests, if the strength increase is
not accompanied by significant increases in electrical
activity, that the same amount of neural drive is able to
activate a larger amount of muscle tissue to produce larger
muscle force.
In the case of (b), this also suggests two possible
mechanisms, namely:
- if the strength increase IS NOT accompanied by a significant
increase in electrical activity, then the same amount of
neural drive is able to activate a larger amount of muscle
tissue to produce larger muscle force. This, of course,
reflects an increase in efficiency or "quality" of
activation.
- if the strength increase IS accompanied by significant
increases in electrical activity, then an increase in neural
drive has increased the number or frequency of muscle fibers
becoming involved in the action. This process does not
reflect an increase in efficiency of activation. Instead it
is a matter of increase due to "quantity" of activity.
In addition, as I mentioned in "Supertraining" (2000, p 33),
maximum strength is produced by an optimum, not a maximal,
frequency of nerve firing.
In the case of the article below, it would appear that the
results reflect an increased efficiency or "quality" of neural
activation, rather than increased "quantity" of activation.
This, of course, is something which is fundamental to what is
known as "optimization", as opposed to maximization in
engineering or production terms. Thus, the same or less
electrical activity of a muscle is not necessarily a sign of
stagnation; it can also reflect greater efficiency or
optimization of what you already have present. So, "less" may
be better, whereas "more" may not be better.
These conclusions are exceptionally important in strength and
power training. If only they would be more widely appreciated
by coaches such as those who work in American football or
rugby, because the belief that bigger is better and stronger
is rife in such circles. More hypertrophy does not necessarily
mean greater strength, as is stated in Mel Siff's
"Supertraining" (2000, p20):
<Optimization of force, torque, speed and power or the
production of 'just the right amount at the right time' of
these motor abilities sometimes seems to be forgotten,
especially in the so-called strength, heavy or contact sports.
All too often, the solution to most performance problems in
such sports seems to be a philosophy of "the greater the
strength and the greater the muscle hypertrophy, the better",
despite the fact that one constantly witnesses exceptional
performances being achieved in these sports by lighter and
less strong individuals.
---------------------
The Effect of Concentric Isokinetic Strength Training of the
Quadriceps Femoris on Electromyography and Muscle Strength in
the Trained and Untrained Limb
Evetovich TK, Housh TJ, Housh DJ, Johnson GO, Smith DB &
Ebersole KT
J of Strength & Conditioning Research: Vol 15, No 4, pp.
439-445
ABSTRACT
The purpose of the present investigation was to examine the
effects of unilateral concentric isokinetic leg extension
training on peak torque (PT) and electromyographic (EMG)
responses in the trained and untrained limbs. Twenty adult men
were randomly assigned to a training or control group. The TRN
group performed 6 sets of 10 leg extensions 3 days per week
for 12 weeks at a velocity of 90°·per sec. All subjects were
tested every 4 weeks for PT and EMG responses of both legs at
a velocity of 90° per sec. The 3-way mixed factorial analysis
of variance (ANOVA) indicated a significant increase in PT
over the 12 weeks in both the trained and untrained limb for
the TRN group but no significant change in PT in either limb
for the CTL group. The results of the 3-way ANOVA for the EMG
data indicated no significant change in EMG amplitude in the
trained or untrained limb for the TRN or CTL EMG may result
from hypertrophic factors and/or changes in the other muscles
or muscle groups involved in leg extension..
------------------------------
INTRODUCTION
It has been suggested that training-induced strength increases
during the first several weeks of a resistance training
program in previously untrained subjects are due, in part, to
neural adaptations that allow for a greater expression of
strength. A number of investigations have attempted to
identify the physiologic mechanisms underlying these neural
adaptations.
For example, Milner-Brown et al have reported more synchronous
motor unit impulses on electromyography (EMG) after isometric
training when compared with pretraining patterns. In addition,
Rutherford and Jones suggested that training establishes new
neural pathways that increase the coordinated activation of
the muscle groups involved in a particular muscle action.
Furthermore, Carolan and Cafarelli proposed that reduced
antagonistic cocontraction of the hamstrings after
isometric training of the leg extensors may be responsible
for the greater torque-producing capabilities of the
quadriceps femoris.
It has also been proposed that training elicits alterations in
the excitatory and/or inhibitory input, so that a greater
inflow of impulses reaches the motor neuron of the working
muscle. Recent investigations have attempted to determine
whether training induces greater motor neuron activation by
monitoring EMG activity over the course of a resistance
training program.
Some studies have indicated that EMG activity increases with
training, supporting the hypothesis of increased neural
activation. Others, however, have reported no such change.
Thus, it remains controversial as to whether an untrained
subject is able to increase strength with training by
increasing the stimulatory input to a working muscle.......
Peak Torque:
The results of the present study indicated that the
concentric isokinetic training resulted in increased PT in
the trained limb. The 15.5% increase in PT across the 12-week
training period (Fig 1) was consistent with the findings of
previous isokinetic training studies, which have reported
increases of 0.5-24%.
EMG:
Previous investigations have reported training-induced
increases in EMG amplitude after concentric isokinetic
training. The results of the present study and those of Komi
and Buskirk, however, indicated that concentric isokinetic
strength training did not result in significantly greater EMG
amplitude values. The reason for the discrepancies between the
results of the present investigation and those of others
examining EMG responses to concentric isokinetic training may
be a function of differences in the procedures used to analyze
and quantify the EMG signal.
The lack of a significant change in EMG amplitude in the
present study (Fig 3 ) indicated that increased PT in the
trained limb was not associated with increased neural drive to
the vastus lateralis. The reason for the increase in PT in the
absence of increased EMG activity is unknown; however,
previous investigations have provided plausible hypotheses:
(a) changes in neural drive to the other muscles or muscle
groups involved in the performance of leg extension, and
(b) muscle adaptations independent of EMG activity.
Changes in Neural Drive to Other Muscles or Muscle Groups
When performing leg extensions, many muscles in addition to
the vastus lateralis are involved. These muscles include (a)
muscles of the stabilizing muscle groups, (b) muscles of the
antagonistic muscle groups, and/or
(c) the other muscles of the quadriceps femoris. Stabilizing
muscle groups involved in leg extension, such as the back,
abdominal, shoulder, and arm muscles, are essential for
maximum peak torque production because they stabilize the
upper body and prevent flexion at the trunk .
Rutherford and Jones have suggested that the ability of the
quadriceps femoris to generate torque may be limited by the
lack of coordinated activation of these muscles. These
investigators reported that an improvement in PT of the leg
extensors after isometric training did not occur until new
neural pathways that coordinated the actions of stabilizing
muscle groups were established. It was suggested that during
muscular training, coordination of the muscles that aid in the
performance of leg extension are involved in a learning
process and that more complex movements may require a longer
learning process. Thus, it is possible that the training in
the present study increased the coordination of the
stabilizing muscle groups, which resulted in increased PT
production.
Another group of muscles that may "learn" to aid in the
expression of leg extension torque are the muscles that are
antagonistic to the quadriceps femoris. Recent evidence
indicates that the levels of antagonistic cocontraction are
modifiable with training. Carolan and Cafarelli measured the
EMG activity in the vastus lateralis and hamstrings after
isometric training of the leg extensors and reported that
there was no change in vastus lateralis EMG activity, but
there was a decrease in hamstring EMG activity. A
training-induced decrease in hamstring coactivation in the
present investigation may have provided less opposing torque
to the contracting quadriceps femoris and resulted in
increased PT production.
This hypothesis is not in accordance with the findings of
Tyler and Hutton , who have suggested that since antagonistic
coactivation reduces the neural drive to the agonists through
reciprocal inhibition, a training-induced reduction in
antagonistic coactivation would allow greater activation of
agonists. If the suggestion of Tyler and Hutton is correct, a
training-induced reduction in hamstring coactivation in the
present study would have resulted in greater activation and,
therefore, greater EMG amplitude in the vastus lateralis.
Measurements of EMG activity in the present study were made
only for the vastus lateralis. It is possible that there may
have been changes in neural drive to the other muscles of the
quadriceps femoris, which could have resulted in an increased
ability to produce torque. Narici et al attributed differences
in the hypertrophic responses of the individual muscles of the
quadriceps femoris to differences in muscle activation after
concentric isokinetic training at a velocity of 120° per sec.
These authors observed preferential hypertrophy and greater
EMG activity in the vastus medialis and rectus femoris when
compared with the vastus lateralis. Thus, there may have been
increased neural activation of the other muscles of the
quadriceps femoris, which resulted in preferential hypertrophy
and increased PT production.
Muscular Adaptations Independent of EMG Activity in the
Trained Limb
Hypertrophic Factors:
As individual muscle fibers enlarge, their positions under
surface electrodes are altered. Therefore, it is possible that
hypertrophy alone could have influenced the EMG signal.
Garfinkel and Cafarelli, however, hypothesized that if
electrode placement is constant, then the electrodes are
detecting EMG over the same area of muscle membrane and,
therefore, hypertrophy would not alter the EMG.
If the hypothesis of Garfinkel and Cafarelli is correct,
hypertrophy of the vastus lateralis could have occurred in the
present study without directly influencing the amplitude of
the EMG signal. In addition to the vastus lateralis, other
muscles involved in leg extension (i.e., stabilizing muscle
groups, rectus femoris, vastus intermedius, vastus medialis,
and other muscles) may have hypertrophied as well.
It is possible that architectural factors that cause or are a
result of hypertrophy of these muscles, yet are independent of
muscle activation, may have contributed to PT production. Such
factors include (a) increased contractile protein content, (b)
increased pennation angles, and/or
(d) changes in tendinous attachments.
Garfinkel and Cafarelli examined the EMG responses of the
vastus lateralis to isometric training and reported that there
was no change in the EMG activity but a 28% increase in PT
production. It was proposed that the increase in contractile
proteins that accompanies muscle training could result in
greater PT simply because each hypertrophied muscle cell is
able to form a greater number of cross-bridges for any level
of activation.
Another architectural factor that is important in the
production of PT, yet is independent of EMG activity, is the
pennation angle. Recent studies have shown that trained or
hypertrophied muscles have pennation angles greater than those
in untrained or atrophied muscles. It has been suggested that
an increase in pennation angles would allow attachment of a
greater amount of contractile tissue to the tendon, which may
result in increased PT production.
It is also possible that the increased collagen synthesis that
has been observed during training-induced muscular hypertrophy
may alter connective tissue attachments. Jones and Rutherford
have suggested that if new attachments were made
intermediately between sarcomeres in series and the tendon,
the tension would not only be transmitted through sarcomeres
in series, but also through intermediate sarcomeres, thereby,
increasing torque production. Thus, it is possible that muscle
hypertrophy, either in the vastus lateralis or other muscles
involved in leg extension, occurred as a result of the maximal
isokinetic training and resulted in increased PT production
that was independent of EMG activity.
Nonhypertrophic Factors
Previous investigations have reported that there may be
qualitative changes in muscle fiber protein expression (i.e.,
fast fiber type conversions from Type IIb to Type IIa) as a
result of resistance training. Although it is not known how
these changes may affect strength, it is possible that the
intramuscular remodeling could contribute to strength gains in
the absence of changes in the EMG....
in muscle force or strength is not necessarily accompanied by
an increase in neural drive or the electrical activity of the
relevant muscles as measured by the EMG. This topic was
addressed in the article below.
This issue is of central importance in all strength training,
because increase in strength classically is recognized to be
the result of:
(a) increased muscle mass (or cross-sectional area),
(b) increased neural drive, or...
(c) a combination of both of the above processes.
The matter of increased neural drive is regarded to be of
special importance during the early stages of training or
retraining (after a prolonged lay-off), because
significant increases in hypertrophy do not usually occur
during such a stage of training, although increases in
strength are very common.
If we examine (a), this suggests, if the strength increase is
not accompanied by significant increases in electrical
activity, that the same amount of neural drive is able to
activate a larger amount of muscle tissue to produce larger
muscle force.
In the case of (b), this also suggests two possible
mechanisms, namely:
- if the strength increase IS NOT accompanied by a significant
increase in electrical activity, then the same amount of
neural drive is able to activate a larger amount of muscle
tissue to produce larger muscle force. This, of course,
reflects an increase in efficiency or "quality" of
activation.
- if the strength increase IS accompanied by significant
increases in electrical activity, then an increase in neural
drive has increased the number or frequency of muscle fibers
becoming involved in the action. This process does not
reflect an increase in efficiency of activation. Instead it
is a matter of increase due to "quantity" of activity.
In addition, as I mentioned in "Supertraining" (2000, p 33),
maximum strength is produced by an optimum, not a maximal,
frequency of nerve firing.
In the case of the article below, it would appear that the
results reflect an increased efficiency or "quality" of neural
activation, rather than increased "quantity" of activation.
This, of course, is something which is fundamental to what is
known as "optimization", as opposed to maximization in
engineering or production terms. Thus, the same or less
electrical activity of a muscle is not necessarily a sign of
stagnation; it can also reflect greater efficiency or
optimization of what you already have present. So, "less" may
be better, whereas "more" may not be better.
These conclusions are exceptionally important in strength and
power training. If only they would be more widely appreciated
by coaches such as those who work in American football or
rugby, because the belief that bigger is better and stronger
is rife in such circles. More hypertrophy does not necessarily
mean greater strength, as is stated in Mel Siff's
"Supertraining" (2000, p20):
<Optimization of force, torque, speed and power or the
production of 'just the right amount at the right time' of
these motor abilities sometimes seems to be forgotten,
especially in the so-called strength, heavy or contact sports.
All too often, the solution to most performance problems in
such sports seems to be a philosophy of "the greater the
strength and the greater the muscle hypertrophy, the better",
despite the fact that one constantly witnesses exceptional
performances being achieved in these sports by lighter and
less strong individuals.
---------------------
The Effect of Concentric Isokinetic Strength Training of the
Quadriceps Femoris on Electromyography and Muscle Strength in
the Trained and Untrained Limb
Evetovich TK, Housh TJ, Housh DJ, Johnson GO, Smith DB &
Ebersole KT
J of Strength & Conditioning Research: Vol 15, No 4, pp.
439-445
ABSTRACT
The purpose of the present investigation was to examine the
effects of unilateral concentric isokinetic leg extension
training on peak torque (PT) and electromyographic (EMG)
responses in the trained and untrained limbs. Twenty adult men
were randomly assigned to a training or control group. The TRN
group performed 6 sets of 10 leg extensions 3 days per week
for 12 weeks at a velocity of 90°·per sec. All subjects were
tested every 4 weeks for PT and EMG responses of both legs at
a velocity of 90° per sec. The 3-way mixed factorial analysis
of variance (ANOVA) indicated a significant increase in PT
over the 12 weeks in both the trained and untrained limb for
the TRN group but no significant change in PT in either limb
for the CTL group. The results of the 3-way ANOVA for the EMG
data indicated no significant change in EMG amplitude in the
trained or untrained limb for the TRN or CTL EMG may result
from hypertrophic factors and/or changes in the other muscles
or muscle groups involved in leg extension..
------------------------------
INTRODUCTION
It has been suggested that training-induced strength increases
during the first several weeks of a resistance training
program in previously untrained subjects are due, in part, to
neural adaptations that allow for a greater expression of
strength. A number of investigations have attempted to
identify the physiologic mechanisms underlying these neural
adaptations.
For example, Milner-Brown et al have reported more synchronous
motor unit impulses on electromyography (EMG) after isometric
training when compared with pretraining patterns. In addition,
Rutherford and Jones suggested that training establishes new
neural pathways that increase the coordinated activation of
the muscle groups involved in a particular muscle action.
Furthermore, Carolan and Cafarelli proposed that reduced
antagonistic cocontraction of the hamstrings after
isometric training of the leg extensors may be responsible
for the greater torque-producing capabilities of the
quadriceps femoris.
It has also been proposed that training elicits alterations in
the excitatory and/or inhibitory input, so that a greater
inflow of impulses reaches the motor neuron of the working
muscle. Recent investigations have attempted to determine
whether training induces greater motor neuron activation by
monitoring EMG activity over the course of a resistance
training program.
Some studies have indicated that EMG activity increases with
training, supporting the hypothesis of increased neural
activation. Others, however, have reported no such change.
Thus, it remains controversial as to whether an untrained
subject is able to increase strength with training by
increasing the stimulatory input to a working muscle.......
Peak Torque:
The results of the present study indicated that the
concentric isokinetic training resulted in increased PT in
the trained limb. The 15.5% increase in PT across the 12-week
training period (Fig 1) was consistent with the findings of
previous isokinetic training studies, which have reported
increases of 0.5-24%.
EMG:
Previous investigations have reported training-induced
increases in EMG amplitude after concentric isokinetic
training. The results of the present study and those of Komi
and Buskirk, however, indicated that concentric isokinetic
strength training did not result in significantly greater EMG
amplitude values. The reason for the discrepancies between the
results of the present investigation and those of others
examining EMG responses to concentric isokinetic training may
be a function of differences in the procedures used to analyze
and quantify the EMG signal.
The lack of a significant change in EMG amplitude in the
present study (Fig 3 ) indicated that increased PT in the
trained limb was not associated with increased neural drive to
the vastus lateralis. The reason for the increase in PT in the
absence of increased EMG activity is unknown; however,
previous investigations have provided plausible hypotheses:
(a) changes in neural drive to the other muscles or muscle
groups involved in the performance of leg extension, and
(b) muscle adaptations independent of EMG activity.
Changes in Neural Drive to Other Muscles or Muscle Groups
When performing leg extensions, many muscles in addition to
the vastus lateralis are involved. These muscles include (a)
muscles of the stabilizing muscle groups, (b) muscles of the
antagonistic muscle groups, and/or
(c) the other muscles of the quadriceps femoris. Stabilizing
muscle groups involved in leg extension, such as the back,
abdominal, shoulder, and arm muscles, are essential for
maximum peak torque production because they stabilize the
upper body and prevent flexion at the trunk .
Rutherford and Jones have suggested that the ability of the
quadriceps femoris to generate torque may be limited by the
lack of coordinated activation of these muscles. These
investigators reported that an improvement in PT of the leg
extensors after isometric training did not occur until new
neural pathways that coordinated the actions of stabilizing
muscle groups were established. It was suggested that during
muscular training, coordination of the muscles that aid in the
performance of leg extension are involved in a learning
process and that more complex movements may require a longer
learning process. Thus, it is possible that the training in
the present study increased the coordination of the
stabilizing muscle groups, which resulted in increased PT
production.
Another group of muscles that may "learn" to aid in the
expression of leg extension torque are the muscles that are
antagonistic to the quadriceps femoris. Recent evidence
indicates that the levels of antagonistic cocontraction are
modifiable with training. Carolan and Cafarelli measured the
EMG activity in the vastus lateralis and hamstrings after
isometric training of the leg extensors and reported that
there was no change in vastus lateralis EMG activity, but
there was a decrease in hamstring EMG activity. A
training-induced decrease in hamstring coactivation in the
present investigation may have provided less opposing torque
to the contracting quadriceps femoris and resulted in
increased PT production.
This hypothesis is not in accordance with the findings of
Tyler and Hutton , who have suggested that since antagonistic
coactivation reduces the neural drive to the agonists through
reciprocal inhibition, a training-induced reduction in
antagonistic coactivation would allow greater activation of
agonists. If the suggestion of Tyler and Hutton is correct, a
training-induced reduction in hamstring coactivation in the
present study would have resulted in greater activation and,
therefore, greater EMG amplitude in the vastus lateralis.
Measurements of EMG activity in the present study were made
only for the vastus lateralis. It is possible that there may
have been changes in neural drive to the other muscles of the
quadriceps femoris, which could have resulted in an increased
ability to produce torque. Narici et al attributed differences
in the hypertrophic responses of the individual muscles of the
quadriceps femoris to differences in muscle activation after
concentric isokinetic training at a velocity of 120° per sec.
These authors observed preferential hypertrophy and greater
EMG activity in the vastus medialis and rectus femoris when
compared with the vastus lateralis. Thus, there may have been
increased neural activation of the other muscles of the
quadriceps femoris, which resulted in preferential hypertrophy
and increased PT production.
Muscular Adaptations Independent of EMG Activity in the
Trained Limb
Hypertrophic Factors:
As individual muscle fibers enlarge, their positions under
surface electrodes are altered. Therefore, it is possible that
hypertrophy alone could have influenced the EMG signal.
Garfinkel and Cafarelli, however, hypothesized that if
electrode placement is constant, then the electrodes are
detecting EMG over the same area of muscle membrane and,
therefore, hypertrophy would not alter the EMG.
If the hypothesis of Garfinkel and Cafarelli is correct,
hypertrophy of the vastus lateralis could have occurred in the
present study without directly influencing the amplitude of
the EMG signal. In addition to the vastus lateralis, other
muscles involved in leg extension (i.e., stabilizing muscle
groups, rectus femoris, vastus intermedius, vastus medialis,
and other muscles) may have hypertrophied as well.
It is possible that architectural factors that cause or are a
result of hypertrophy of these muscles, yet are independent of
muscle activation, may have contributed to PT production. Such
factors include (a) increased contractile protein content, (b)
increased pennation angles, and/or
(d) changes in tendinous attachments.
Garfinkel and Cafarelli examined the EMG responses of the
vastus lateralis to isometric training and reported that there
was no change in the EMG activity but a 28% increase in PT
production. It was proposed that the increase in contractile
proteins that accompanies muscle training could result in
greater PT simply because each hypertrophied muscle cell is
able to form a greater number of cross-bridges for any level
of activation.
Another architectural factor that is important in the
production of PT, yet is independent of EMG activity, is the
pennation angle. Recent studies have shown that trained or
hypertrophied muscles have pennation angles greater than those
in untrained or atrophied muscles. It has been suggested that
an increase in pennation angles would allow attachment of a
greater amount of contractile tissue to the tendon, which may
result in increased PT production.
It is also possible that the increased collagen synthesis that
has been observed during training-induced muscular hypertrophy
may alter connective tissue attachments. Jones and Rutherford
have suggested that if new attachments were made
intermediately between sarcomeres in series and the tendon,
the tension would not only be transmitted through sarcomeres
in series, but also through intermediate sarcomeres, thereby,
increasing torque production. Thus, it is possible that muscle
hypertrophy, either in the vastus lateralis or other muscles
involved in leg extension, occurred as a result of the maximal
isokinetic training and resulted in increased PT production
that was independent of EMG activity.
Nonhypertrophic Factors
Previous investigations have reported that there may be
qualitative changes in muscle fiber protein expression (i.e.,
fast fiber type conversions from Type IIb to Type IIa) as a
result of resistance training. Although it is not known how
these changes may affect strength, it is possible that the
intramuscular remodeling could contribute to strength gains in
the absence of changes in the EMG....