In our quest to understand, and eventually prevent, the loss of muscle strength and mass that occurs during prolonged periods in microgravity, we have organized our research approach by systems and useful terrestrial analogs. Our hypothesis was that: The eccentric movement, or lengthening component, of dynamic, resistive exercise, is required for the production of the greatest gains in strength and muscle hypertrophy in the most metabolically efficient, and time effective manner. The exercises selected were leg presses, leg (knee) extensions, and hamstring curls. In this 30 week study, 38 male subjects, between the ages of 25 and 50, were divided into four groups. One group performed 5 sets of 8-12 repetitions per set of conventional concentric/eccentric (CON/ECC) exercises. Another group performed only the concentric (CON) movement on the same schedule. The third group performed twice the number of sets in the concentric only mode (CON/CON), and the last group served as controls. We interpret these data as convincing evidence that the eccentric component of heavy resistance training is required along with the concentric for the most effective increase in strength and muscle fiber size in the least time. We also conclude that such heavy exercise of any such muscle group need not consume inordinately long periods of time, and is quite satisfactorily effective when performed on 72 hour centers

Buchanan, Paul

Dudley, Gary A.

Hather, Bruce M.

Tesch, Per A.

English

NASA Technical Reports Server

(NASA-TM-111111) MUSCLE N96-13368
PRESERVATION IN LONG DURATION SPACE
MISSIONS: THE ECCENTRIC FACTOR
(NASA. Kennedy Space Center) 19 p Unclas
G3/52 0073747
https://ntrs.nasa.gov/search.jsp?R=19960003359 2020-06-16T05:38:58+00:00Z
NASA-TM-111111
'<??o -
213
MUSCLE PRESERVATION IN LONG DURATION SPACE MISSIONS:
THE ECCENTRIC FACTOR.
Paul Buchanan, M.D., Gary A. Dudley, Ph.D., Per A. Tesch,
Ph.D., and Bruce M. Hather, Ph.D.
(From the Biomedical Operations and Research Office of The
JOHN F. KENNEDY SPACE CENTER, NASA, with Prof. Tesch
visiting from the Karolinska Institute, Stockholm, Sweden.)
INTRODUCTION
In our quest to understand, and eventually prevent, the loss
of muscle strength and mass that occurs during prolonged
periods in microgravity, we have organized pur research
approach by systems and useful terrestrial analogs.
(Slide #1)
In previous papers and presentations at earlier Ninon
University symposia I have described our progression through
this program plan. Our work in electromyostimulation and
tissue analysis following, 30 days of 6 degree head down
bedrest, have been the primary subjects of these reports.
It should, perhaps, be repeated that the reasons for
undertaking this work are two fold. First, the problem of
muscle loss in the microgravity environment is very real and
methods used to date have not been fully successful in
preventing this change. The loss is deleterious to the
crewpersons postflight activities, potentially life
threatening if full physical vigor is required in a descent
and landing emergency, and not with out impacts to the
individual ego. The second problem concerns the operational
impact of attempts to maintain muscle mass and strength in
space. Past experience with exercise programs lasting 2 to
4 hours daily have been, as stated in other published
observations, disappointing in terms of results, and the
inordinate amount of time removed from the work schedule
increases the expense of productivity in space. We must
also consider the volume in cubic meters required for
exercise equipment, the disturbances to microgravity
critical activities caused by vibrations from treadmills,
and in some projected cases, the electrical power that could
be removed from this already overtaxed resource.
With all of the foregoing in mind, it behooves us to be
certain we understand the cellular as well as the gross
physical nature of the problem and thus to be able to
prescribe an exercise program that addresses the known,
specific elements.
In the 1988 symposium, I reported the results of the joint
Kennedy Space Center - Ames Research Center 30 day bedrest
study. Our primary interests were the changes in the
cellular morphology and biochemistry of the vastus lateralis
and soleus muscles after 30 days of uninterrupted 6 degrees
head down bedrest. The finding that type 1 or slow twitch
fibers did not preferentially atrophy contrasts with the
reported changes in the muscles of the suspended rodent
model. Moreover, bedrest decreased the activity of enzymes
of aerobic, but not anaerobic metabolism. An intervention
group that received electromyostimulation showed less signs
of deconditioning. Details of this research have since been
published in a series of papers in Aviation, Space, and
Environmental Medicine, volume 60, 1989.
Our primary thrust since the bedrest effort has been toward
understanding the elements required for muscle hypertrophy.
PROBLEM STATEMENT
It is tempting to assume that the elements necessary for
building muscle mass are well understood. Books' and
magazine articles have been written on the subject for over
100 years. Yet minimal scientific research has been done on
humans to verify claims made for the methods promulgated in
these writings. Since the late 1940s magazines catering to
the interest in weight lifting and bodybuilding have crowded
the news stands, and each month a new method for creating
larger muscles in some part of the body is the cover story.
(Slide #2)
Indeed, quite startling examples of human muscular
development are readily available, and the owners of these
physiques are well paid for revealing their training
methods. But a clear scientific judgment of these methods
cannot be made without experimental data, and what worked
for Arnold Schwartzenegger, starting at age 19, is not
necessarily a reasonable plan for a more mature person
starting from a more sedentary life style.
Not only is it necessary for us to understand such things as
intensity, duration, and frequency of stresses to be placed
on individual muscle groups, but it is important that we
learn the most simple and effective way of administering
that stress. We must learn whether or not the dynamic
movements involved in the lifting of free weights on Earth
is significantly more effective than isokinetically limited
movements or isometric contractions. We must also better
understand the metabolic demands of selected exercises and
the most constructive period of rest between bouts of
exercises.
In formulating the methods to be used in our first attack on
the problem of creating measurable muscle fiber hypertrophy,
two guiding limitations were imposed. First, the exercise
required must be of a commonly accepted type, with at least
some basis in experience that would lead us to expect
positive results. (The opposite end of this would be
electromyostimulation, for which every element is
controversial.) The second limitation was, that we had to
have some reasonable expectation of providing equipment and
cubic area in the space habitat to permit these exercises.
Following a rather interesting process of elimination, the
quadriceps femoris was chosen as the muscle group, dynamic,
isotonic like, movements were selected as the most natural
and commonly used in training exercises, and eccentric, or
lengthening muscle actions, were selected as the movement
component to evaluate for relative effectiveness and
necessity. The reason is, of course, that muscle is
substantially loaded during eccentric actions in 1-gravity,
with essentially the complete loss of such muscle action in
microgravity.
1
HYPOTHESIS
Our hypothesis was that: The eccentric movement, or '
lengthening component, of dynamic, resistive .exercise, is
required for the production of the greatest gains in
strength and muscle hypertrophy in the most metabolically
efficient, and time effective manner.
METHODOLOGY
The exercises selected were, (1) leg presses,
(2) leg (knee) extensions,
.(Slide ~f 4)
and (3) hamstring curls.
(Slide f5)
In this 30 week study, 38 male subjects, between the ages of
25 and 50, were divided into four groups. One group
performed 5 sets of 8-12 repetitions per set of conventional
concentric/eccentric (CON/ECC) exercises. Another group
performed only the concentric (CON) movement on the same
schedule. The third group performed twice the number of
sets in the concentric only mode (CON/CON) , and the last
group served as controls. The maximum reasonable resistance
training loads were selected for each individual during the
equipment and methods familiarization period that lasted for
4 weeks and ended one week prior to the experimental
training. During this time, all subjects were tested for
their 3 repetition maximum strength in the leg press and
knee extension exercises. Each exercise was performed with
concentric only or concentric and eccentric muscle actions
in each repetition. Subjects were again tested after 20
weeks of training, and then after 4 weeks of detraining.
Each group trained twice weekly with at least 48 hours of
rest required between sessions. Training sessions were
under strict supervision with encouragement and guidance
given to each subject on a one-to-one personal basis. These
sessions lasted from 30 to 40 minutes, and each set was
performed to failure. Careful records were maintained by
the training supervisors of the weight used in each exercise
set, and the number of repetitions fully completed.
The equipment used in the training was unique in that it was
customized to our particular requirements. Each piece was
tested for differential friction losses in either the
concentric or eccentric mode, and linearity of resistance.
We discovered that friction losses in certain popular
commercial knee extension and flexion machines were in
excess of 25%. This resulted in an unacceptable decrease of
the force presented to the subjects in the eccentric mode,
and required extensive rebuilding of the machines with
replacement of the proprietary cam/pulleys and bearings.
(Slide #6)
The other custom feature of these pieces of resistive
exercise equipment is the addition of hydraulic cylinders.
These were selectively attached to the weight stacks to
remove the eccentric component of the exercises. Since the
same equipment was used for all three groups, it was
necessary to assure that the concentric component was not
altered by these modifications. The relatively small
resistance added by the hydraulic cylinder was, therefore,
counterweighted.
Two needle biopsies, after the method of Bergstrom, of the
right side vastus lateralis, were taken from all subjects
before the beginning of heavy training. Two more biopsies
were taken from adjacent sites at the end of 20 weeks of
training, and again after 30 days of detraining.
RESULTS
STRENGTH AND METABOLIC RESPONSES TO TRAINING
(slide »7)
The concentric/eccentric training group, CON/ECC, increased
leg press strength more than the concentric only, CON,
training group (P<0.05) when the testing exercise was
performed with both concentric and eccentric actions. The
relative group increases were 26% and 8%.
(slide #8)
When the testing was only in the concentric mode, the
CON/ECC group improved 22%, the CON group 12%.
Detraining for one month resulted in modest changes in
strength, but group CON/ECC was still stronger than before
training while group CON was not. (In both cases P<0.05.)
1
The energy cost for a given training session using the
supine leg press exercise was approximately 75 kcal for both
groups. This occurred in spite of the fact that group
CON/ECC performed almost twice the total work as group CON;
4358 + 288 kg'm versus 2551 + 192 kg'm mean + SE. The
modest additional energy cost of adding eccentric muscle
actions to the training program and the benefit of a large
increase in the load acted against, probably reflects the
high efficiency of performing this type of muscle action.
MUSCLE FIBER TYPE HISTOCHEMICAL CHANGES WITH TRAINING
(Slide #9)
A marked decrease in type 2b fibers, to approximately 1%,
was found post-training in both groups CON/ECC and CON,
(P<0.05).
(Slide #10)
At the same time the percent of type 2a fibers was increased
to a level very nearly equal to the percent loss of type 2b.
This occurred to a similar relative extent in both groups,
(P<0.05). After one month of detraining, type 2b fibers
were beginning to return in group CON. This was not the
case in group CON/ECC.
Because the type 2b percentage was extremely low both post-
training and detraining, valid and reliable cross sectional
area and capillary count data could not be determined on
this fiber type at these times. Accordingly, the area and
capillary data are reported for type 1 fibers and all type 2
fibers.
(Slide #11)
Group CON showed evidence of hypertrophy post-training for
type 2 fibers (15% increase, P<0.05) but not Type 1 fibers
(<10% increase, P>0.05). After one month of detraining the
cross sectional area of both fiber types was only 5% larger
than before training (P>0.05).
(Slide #12)
Group CON/ECC showed stronger evidence of hypertrophy. The
cross sectional area of type 1 and type 2 fibers was 11% and
30% larger, respectively, post-training. Moreover, they
were still 12% and 21% larger, respectively, after one month
of detraining. These results indicate the addition of
eccentric muscle actions to resistance training resulted in
greater hypertrophy of mainly type 2 fibers, which was
maintained to a greater extent after cessation of training.
(Slide #13)
This is supported by the fact that the ratio of the cross
sectional area of type 2 to type 1 fibers was increased
(P<0.05) both post-training and detraining for group
CON/ECC, but not group CON.
(Slide 114)
The number of capillaries around type 1 and type 2 fibers
was increased 18% and 25%, respectively, for group CON/ECC
post-training, and 29% and 32% after detraining. (P<0.05 in
both cases.)
(Slide #15)
Group CON showed similar increases for type 1 and type 2
fibers post-training (30% and 36%) and detraining (32% and
40%, P<0.05 in all cases). .
(Slide #16)
As a result of these responses and the modest hypertrophy
shown by group CON, the number of capillaries per unit area
of type 1 and type 2 fibers was increased post-training and
detraining more for this group than for CON/ECC.
(Slide #17)
Group CON/ECC showed a similar response for type 1 fibers
after detraining. The substantial hypertrophy of the type 2
fibers in this group, however, offset the neoformation of
capillaries such that the capillarity per unit area of the
type 2 fibers did not change with training or detraining for
group CON/ECC. The proliferation of capillaries with
resistance training has not generally been reported. It may
be that the supine nature of the leg press exercise used in
this study placed a greater stress on the peripheral
circulation than conventional resistance training in the
upright posture. This requires further verification and
should be pursued since the supine posture imposes
cardiovascular stresses more analogous to null gravity than
upright exercise. Nevertheless, the data indicate this type
of training can cause substantial hypertrophy without
compromising the capillary supply of muscle.
Data from the experimental group that performed twice the
number of concentric only exercises, group CON/CON, have not
been presented here. Some tissues have not been completely
evaluated. We can, however, safely make certain general
statements from the data that are available. The time
required for completion of an exercise session was nearly
twice that required for group CON/ECC, and the energy cost
for n given training session was nearly doubled. In spite
of thin, the gains in strength were clearly less than those
of group CON/ECC, though greater than group CON.
SUMMARY
\ . , •
We interpret these data as convincing evidence that the
eccentric component of heavy resistance training is required
along with the concentric for the most effective increase in
strength and muscle fiber size in the least time. We also
conclude that such heavy exercise of any such muscle group
need not consume inordinately long periods of time, and is
quite satisfactorily effective when performed on 72 hour
centers.
T[f I may extrapolate from our present data to the
environment of the microgravity habitat, it seems reasonable
to conclude that the long periods of time devoted to
attempts at maintaining muscle strength and mass might be
shortened. Further, based on these data and other work from
our laboratories by Convertino and others, daily exercise
for two hours or more may be unnecessary for the maintenance
of aerobic capacity. If more effective muscle maintenance
can be performed in less time and with less than daily
impact on the crew duty schedule, and if a single bout of
maximal aerobic exercise on 5 or 7 day centers can maintain
cardiopulmonary capacity, then expensive non productive crew
time can be significantly reduced.
The negative effect of these findings, as stated earlier,
may be in the creation of hardware that can be used in
microgravity to provide the balanced concentric/eccentric
resistance for all th$ major muscle groups. Ideally, such a
device should be isolated in regards to any vibration
produced. For the currently planned space station,
equipment with electromagnetic or electrohydraulic
requirements could result in severe limits on the time
available for use. .A purely mechanical device that can be
adequately calibrated for long periods, should be nearly
ideal. We have assembled a candidate devise in our
laboratory at Kennedy Space Center, based on a commercially
available mechanical load cell. ..A testing program is
currently in progress. .
(Slide «18 and #19)
CONCLUSION
In order to gain enough confidence in these presented data
to bring about a major influence on planning of future space
missions, methodologies similar to those described must be
applied to an extended hypokinetic, hypodynamic model, such
as bedrest. An unlikely alternative would, of course, be
an extended, well.controlled trial in the actual space
environment. Whichever method is eventually pursued, it is
obvious that the problems of muscle wasting,-and the most
effective and productive use of crew time must be given a
higher priority as our several space agencies move toward a
serious manned space exploration initiative. .
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Muscle preservation in long duration space missions: The eccentric factor

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