Supertraining

--- In [EMAIL PROTECTED], "[EMAIL PROTECTED]" <[EMAIL PROTECTED]> wrote:
>
> I remember reading about trainees who could only train one arm or one leg due 
> to injury experiencing a training effect on the untrained limb. For example a 
> skier broke his right leg and could only train his left leg. But when the 
> cast was removed there was less atrophy in his right leg than was expected.
> 
> Is this effect a myth or is there substance to the story?
> 

*************
The below excerpts should hopefully provide some answers:

Cross Education and the Human Central Nervous System Mechanisms of Unilateral 
Interventions Producing Contralateral Adaptations
BY TIBOR HORTOBAGYI
IEEE ENGINEERING IN MEDICINE AND BIOLOGY MAGAZINE

Chronic unilateral motor activity affects the motor
output of the contralateral homologous muscle.
Such adaptation, or "cross education," indicates an
organizational and functional role for the contralateral
elements of the central nervous system. In this article,
cross education is used as a model to examine the contralateral
organization of the human central nervous system.
The first evidence for cross education appeared in psychomotor
literature over a century ago. A flurry of subsequent
studies confirmed the phenomenon of cross education using
chronic voluntary, imagined, stimulated contractions of large
antigravity and small hand muscles. The magnitude of cross
education is normally about 25%, but in a few cases, force or
skill transfer reached 80%. The hallmarks of these adaptations
are that the amount of force or skill transfer is proportional to
the gains in the trained muscle. These gains in function are
also highly specific to the involved muscle pair, independent
of limb dominance, age, and gender. Cross education in the
"untrained" muscle can also occur in the absence or presence
of muscle activity.
The contralateral changes can be clinically meaningful.
Nerve damage on one side causes the death of motoneurons
innervating the homologous muscle on the contralateral side.
Clinically meaningful improvements in force or skill transfer
or reductions in deficit occur from one side of the body to the
other in patients with spinal cord injury, selected neuromuscular
disorders, spastic hemiparesis, knee arthroplasty, and in
patients with orthopedic deficits.
The neural mechanisms of these transfers from one side of
the body to the other are unknown. In this article, we examine
the possibility of whether there are direct changes in the
excitability of transcallosal paths and whether, linked to
these changes, there are indirect modulations in the excitability
of contralateral corticospinal projections. Thus, unilateral
practice would affect interhemispheric inhibition and, subsequently,
it would also modify the excitability of the contralateral
corticospinal projections, mediating cross
education. Finally, we explore the possibility that there is a
spinal component in cross education. The behavioral and
neuroanatomical data suggest that the unilateral exercise
model could provide significant functional and conceptual
insights into how the two hemispheres and segmental connections
are organized and how they operate in humans.

Behavioral Changes Produced by Unilateral
Motor Activity: Cross Education
Chronic unilateral motor activity can enhance or modify the
performance of the contralateral homologous muscle. The first
evidence of the cross education phenomenon appeared in psychomotor
literature over a century ago (for a review, see [1]).
A flurry of subsequent experiments confirmed the phenomenon
using a variety of paradigms, including chronic voluntary,
imagined, and stimulated contractions of large antigravity and
small intrinsic hand muscles. Most studies using chronic unilateral
motor activity observed cross education in the contralateral
homologous muscle [1].
Cross education is specific to the homologous muscle pair.
After chronic strength training with maximal voluntary contractions
(MVCs), the strength of the MVC increases 30–40%
in the trained muscle. The average gain in MVC is about 20%
in the "nonexercised" contralateral homologous muscle without
changes in nonhomologous muscles. When a subject is
instructed to perform an MVC of a muscle on one side of the
body, the concurrent surface electromyograph (EMG) activity
can reach 15% of maximum in the homologous muscle pair
[2], and even submaximal contractions on one side of the body
can produce such concurrent activity [3]. However, this concurrent
activity can be completely absent. When asked, subjects
are able to minimize or completely suppress this
concurrent activity (surface EMG < 50 ìV), and there is no
evidence to suggest that this suppression affects the post-training
MVC in the muscles on the opposite side [4]. These EMG
observations suggest a high level of specificity associated with
cross education. This specificity is somewhat perplexing.
While training with unilateral MVCs, there may be some concurrent
EMG activity in the homologous as well as in nonhomologous
muscles, but an increase in performance only occurs
in the homologous muscle. For example, we observed EMG
activity in upper extremity muscles while leg muscles were
exercised, but cross education occurred only in the homologous
leg muscle without improving grip strength [2], [5].
Another aspect of specificity in cross education is related to
the type of muscle contraction. When subjects exercise with
lengthening MVCs, the magnitude of cross education tends to
be the greatest in voluntary strength measured with lengthening
compared to shortening or isometric contractions, especially
when high-velocity contractions are used [2], [5], [6].

Chronic strength training with electrical stimulationevoked
contractions also produces substantial cross education
in sedentary young subjects [2], [8]. For example,
electrical stimulation-evoked isometric contractions of the
triceps surae over 21 sessions resulted in a 40% increase in
muscle strength of the contralateral ankle plantar flexors [8].
A remarkable feature of these adaptations is that both electrically
evoked and voluntary force production increased after
training. A potential confounding factor with electrical stimulation-
evoked contractions in humans, as seen in previous
studies [2], [8], is that it is difficult to determine whether
subjects also voluntarily contract the muscles that are being
stimulated and thus augment the force production that is
intended to be produced solely by the percutaneous stimulation.
In experiments on patients with spinal cord injury,
chronic eight-hour-per-day functional electrical stimulation
resulted in significant stimulation-evoked forces in the contralateral
homologous muscles of the hand, confirming the
findings in intact humans [9]. Taken together, the data indicate
that perhaps spinal paths in combination with interhemispheric
mechanisms may be involved in cross education.

Cross education is not solely produced by physically executed
muscle contractions. Imagined maximal voluntary contractions
of a small hand muscle can also produce cross
education [12]. MVC of the hypothenar muscle, which was
completely electrically silent during the four-week training
program, increased significantly by 10%. These improvements
in MVC occurred without changes in twitch force, suggesting
that adaptations occurred in the areas of the motor strip that
are associated with motor programming and execution.
However, these findings can be muscle specific. Chronic
strength training with imagined contractions of the elbow flexor
muscles did not increase voluntary activation, and imagined
training did not increase maximal voluntary strength, even in
the trained muscles [13]. One possibility is that larger motor
cortical areas are involved in an imagined contraction of the
small hypothenar muscle compared with the large elbow flexors,
and this larger cortical involvement could be more effective
in increasing strength in a small muscle.

Cross education observed in clinical conditions represents
the other end of the spectrum. A clinically meaningful amount
of force or skill or even functional deficit can be transferred
from one side of the body to the other in patients with spinal
cord injury [9], selected neuromuscular disorders [16], spastic
hemiparesis [17], knee arthroplasty [18], and those with orthopedic
deficits [19]. For example, patients who participated in a
contralateral therapy program after immobilization of one arm
due to a surgical procedure experienced an increase in the
range of motion of the finger and wrist joints and in handgrip
force compared with unexercised controls [19]. Long-term
electrical stimulation of hand muscles on one side in quadriplegics
increased electrical stimulation-evoked force in the
same, but in no other muscles on the contralateral side [9].
Knee arthroplasty patients also revealed impaired proprioception
in their nonaffected knee compared with age-matched
controls [18]. There is also evidence that operant conditioning
in primates (including humans) can up and down regulate the
magnitude of stretch reflex on the contralateral side in
humans and intact and spinal mammals [20]. Most recently,
Strens et al. reported that the ipsilateral human motor cortex
can functionally compensate for acute contralateral motor
cortex dysfunction in stroke patients [21].

There is an abundance of evidence to suggest that chronic
activation of muscles on one side of the body produces adaptations
in the same muscles on the other side of the body in
healthy adults as well as in individuals with a variety of
pathologies. Data inferred from cross-sectional studies make
it likely that interhemispheric and spinal paths both contribute
to cross education. During a unilateral muscle contraction,
not only is there an increase in the activity in the
M1 that produces the motor activity, but there also is a large
increase in activity in the ipsilateral M1 with its associated
muscles being most often completely electrically silent.
Although interhemispheric callosal paths in humans are
moderate to dense, with the majority of the interhemispheric
connections being inhibitory, the connections between the
homologous muscles tend to be excitatory, providing a neuroanatomical
basis for cross education. The possibility exists
that the effects of unilateral practice on interhemispheric
inhibition and on the excitability of the contralateral corticospinal
projections are linked, and these effects are graded
according to the nature of muscle activation. The possibility
also exists that cross education is mediated by cross-spinal
paths. Cutaneous stimulation appears to exert strong excitatory
effects on contralateral motoneurons. In total, an understanding
of interhemispheric interactions in the human motor
cortex may shed light on the mechanisms of motor learning..

===================
Jamie Carruthers
Wakefield, UK