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[A1CR]

A question that occurs to some who initiate CR is whether CR
will affect
their ongoing exercise abilities. The paper below appears to
address such questions and the results appear to indicate
that muscle and
aerobic abilities, relative to the reduced body size of the
CRer, do not
suffer significantly from CR, but are improved for the
exercised subjects.
The word http://en.wikipedia.org/wiki/Torque appears to be
in 100
http://en.wikipedia.org/wiki/Newtons for the values in some
of the tables.

Weiss EP, Racette SB, Villareal DT, Fontana L, Steger-May K,
Schechtman KB,
Klein S, Ehsani AA, Holloszy JO.
Lower extremity muscle size and strength and aerobic
capacity decrease with
caloric restriction but not with exercise-induced weight loss.
J Appl Physiol. 2006 Nov 9; [Epub ahead of print]
PMID: 17095635

Caloric restriction (CR) results in fat loss; however, it
may also result in
loss of muscle and thereby reduce strength and aerobic capacity
(V^O(2)^max). These effects may not occur with
exercise-induced weight loss
(EX) because of the anabolic effects of exercise on heart
and skeletal
muscle. We tested the hypothesis that CR reduces muscle size
and strength
and V^O(2)^max while EX preserves or improves these
parameters. Healthy 50-
to 60-year-old men and women (BMI 23.5-29.9 kg/m(2)) were
studied before and
after 12 months of weight loss by CR (n=18) or EX (n=16).
Lean mass was
assessed by DXA, thigh muscle volume by MRI, isometric and
isokinetic knee
flexor strength by dynamometry, and treadmill V^O(2)^max by
indirect
calorimetry. Both interventions caused significant decreases
in body weight
(CR: -10.7+/-1.4%, EX: -9.5+/-1.5%) and lean mass (CR:
-3.5+/-0.7%,
EX: -2.2+/-0.8%), with no significant differences between
groups.
Significant decreases in thigh muscle volume (-6.9+/-0.8%)
and composite
knee flexion strength (-7.2+/-3%) occurred in the CR group
only. Absolute
V^O(2)^max decreased significantly in the CR group
(-6.8+/-2.3%), whereas
the EX group had significant increases in both absolute
(+15.5+/-2.4%) and
relative (+28.3+/-3.0%) V^O(2)^max. These data provide
evidence that muscle
mass and absolute physical work capacity decrease in
response to 12 months
of CR, but not in response to a similar weight loss induced
by exercise.
These findings suggest that during exercise-induced weight
loss, the body
adapts to maintain or even enhance physical performance
capacity.

... While caloric restriction (CR) is an effective means for
achieving
weight loss, the negative
energy balance induced by CR may result not only in
reductions in fat mass
but also in
catabolism of skeletal muscle and myocardium, thus affecting
the capacity to
perform
physical work. Indeed, previous studies have demonstrated
that CR-induced
weight loss
is associated with decreases in muscle size (6, 7, 13, 14)
and strength (8,
10).
Furthermore, because fat free mass is a strong determinant
of aerobic
exercise capacity
(V^O(2)^max) (5), CR may also decreaseV . O2max.
An increase in exercise energy expenditure, without a
compensatory increase
in
food intake, is also an effective means for achieving weight
loss (12, 14,
15). Negative
energy balance occurs in humans and animals during
catastrophic events, such
as
escaping from environmental disasters (floods, forest fires,
earthquakes),
avoiding
predators (as, for example, when an animal's territory is
invaded by
another, more
powerful species), or escaping from, or participating in
war. In this
context, the ability to
preserve or improve strength and aerobic capacity, despite a
negative energy
balance,
might have been selected for during the course of evolution
because it
provided a survival
advantage. While the preservation of strength and aerobic
capacity may not
be
important in modern society for the purposes of avoiding
predators, etc.,
decrements in
strength and aerobic capacity may be predisposing factors
for physical
frailty in late life
(3, 4).
The purpose of the present study was to test the hypothesis
that CR results
in
decreases in muscle size and strength and in aerobic
exercise capacity,
while a similar
energy deficit induced by increasing exercise energy
expenditure without
changing
energy intake (EX) does not alter muscle size or strength
and likely
increases aerobic
capacity. The data reported in this paper were obtained as
part of a larger
investigation of
the feasibility of CR in healthy volunteers (CALERIE:
Comprehensive
Assessment of
Long-term Effects of Reducing Intake of Energy) (12).
... Participants. Fifty- to sixty-year-old men and women,
with body mass
index
(BMI) values in the high-normal to overweight range (i.e.
23.5-29.9 kg/m2)
were
recruited from the Saint Louis metropolitan area. Candidates
for the study
were excluded
if they had: 1) a history of diabetes or a fasting blood
glucose value
=/>126 mg/dL, 2) a
history or clinical evidence of coronary artery disease,
stroke, or lung
disease, 3) a resting
blood pressure =/>170 mmHg systolic or 100 mmHg diastolic,
or 4) a recent
history or
evidence of malignancy. Furthermore, all candidates had to
be non-smokers
and
sedentary (defined as exercising less than 20 minutes per
day, twice per
week during the
6 months before baseline testing). Women had to be
postmenopausal. ...
The participants were randomly assigned, with stratification
for sex, to the
CR,
EX, or a control group in a 2:2:1 ratio. Among the 19
subjects in the CR and
EX groups ... 18 in each
group completed the study. ... complete outcome data
were only available on 4 of the 10 participants who were
randomized to the
control
group; therefore, the control group data were not included
in the analyses
... data from 34 subjects (CR: n=18; EX: n=16) are included
in the present
report. ...

RESULTS
Participants. The male/female distribution was similar in
the CR (7 men, 11
women) and EX (6 men, 10 women) groups. Mean age (± SD) for
both groups was
in the
middle to upper end of the targeted age range for the study
(CR: 55.2±3.4
yr; EX:
59.4±1.0 yr). Baseline BMI (mean±SD) was 27.1±2.5 kg/m2 in
the CR group and
27.0
± 1.8 kg/m2 in the EX group reflecting the fact that most of
the
participants were
overweight.
Protein Intake. Absolute protein consumption (g/day)
decreased significantly
in
the CR group but not in the EX group (Table 1). When
expressed relative to
body weight,
protein consumption did not change in the CR group but
increased
significantly in the EX
group (Table 1). The between-group comparisons of changes in
absolute and
relative
protein consumption were both marginally significant.

Table 1. Protein consumption, lean mass, and thigh muscle size.
===========================================================
CR (n=18) EX (n=16) P Between group
===========================================================
Protein consumption, g/day
Baseline 88±6 83±5
Average during intervention 80±4 87±6
Change, g/day -7.3±3* 3.1±3 0.03
Change, % -5.9±4 4.7±4 0.06
Protein consumption, g/kg/day
Baseline 1.11±0.051.09±0.04
Average during intervention 1.11±0.06 1.23±0.07
Change, g/kg/day 0.003±0.04 0.14±0.05 *0.05
Change, % 1.7±4 13.1±4* 0.06
Lean mass
Baseline, kg 49.1±2.4 47.9±2.8
Final, kg 47.4±2.4 46.8±2.6
Change, kg -1.6±0.3* -1.2±0.3* 0.41
Change, % -3.4±0.7* -2.3±0.7* 0.31
Thigh muscle volume, cm^3
Baseline 1529±80 1516±81
Final 1413±67 1532±86
Change, cm^3 -110±15* 7.95±17 <0.0001
Change, % -6.9±0.8* 0.49±1.0 <0.0001
Thigh muscle CSA, cm^2
Baseline 191±10 190±10
Final 177±8.4 192±11
Change, cm^2 -13.8±1.8* 0.99±2.2 <0.0001
Change, % -6.9±0.8* 0.49±1.0 <0.0001
===================================================
Data are arithmetic means±SE except for change data
which are least
squares means±SE from the ANCOVA with Baseline value and
percent change in
weight as covariates.
* P </=0.05 versus zero by ANCOVA with Tukey adjustment
for multiple
comparisons.
For protein consumption data, "average during
intervention" reflects the
mean of data collected at 1, 3, 6, 9, and 12 months during
the intervention
and sample sizes in the EX group are 1 less than listed in
table header.
Thigh muscle size data represent the sum of the right and
left thighs and
sample sizes for the CR and EX groups are 1 and 4 less than
listed in table
header, respectively.
CSA, cross-sectional area.

Body Weight and Lean Body Mass. As we reported previously
for a slightly
larger sample (12; 20), body weight decreased significantly
in both the CR
(-8.1±1.1 kg,
-10.7±1.4%) and EX (-7.7±1.2 kg, -9.5±1.5%) groups and these
changes were
not
different between groups whether expressed in absolute terms
(p=0.80) or as
a percentage
(p=0.58). Likewise, lean body mass decreased significantly
in both groups
and these
changes were not different between groups (Table 1).
Thigh Muscle Volume. Thigh muscle volume and average thigh
muscle CSA
decreased significantly the CR group but not in the EX group
and these
changes were
significantly different between groups (Table 1). In the CR
group, the
decrease in thigh
muscle volume correlated with the magnitude of change in
body weight while
in the EX
group there was no evidence for such a relationship (Figure
1). The
comparison of
correlation coefficients between groups did not achieve
statistical
significance.
Muscle Strength. Isokinetic knee flexion torque decreased
significantly in
the
CR group and remained unchanged in the EX group (Table 2 and
Figure 2). The
between-group comparison of these changes was significant
when expressed as
a
percentage. Isometric knee flexion did not change
significantly in either
the CR or EX
groups (Table 2 and Figure 2). Composite knee flexion
strength decreased
significantly in
the CR group and remained unchanged in the EX group; these
changes were
statistically
different between groups whether expressed in absolute terms
or as a
percentage (Table 2
and Figure 2).

Table 2. Isokinetic and isometric knee flexor strength.
===========================================================
CR (n = 15) EX (n = 12) P (Between group)
===========================================================
Torque (raw)
Peak torque at 60°/s
Baseline, Nm 98±6 80±8
Final, Nm 91±6 83±7
Change, Nm -6.1±3* 1.2±3 0.11
Change, % -6.6±3* 4.3±3 0.02
Peak torque at 0°/s
Baseline, Nm 95±8 73±7
Final, Nm 88±7 79±7
Change, Nm -5.9± 4 4.7±5 0.16
Change, % -5.4±6 11.0±7 0.11
Sum of 0 and 60°/s peak torques
Baseline, Nm 193±14 152±14
Final, Nm 178±13 162±14
Change, Nm -13.3±6* 7.5±7 0.04
Change, % -7.2±3* 7.2±4 0.02
Torque relative to body weight
Peak torque at 60°/s
Baseline, Nm/kg 1.24±0.06 1.06±0.08
Final, Nm/kg 1.29±0.06 1.23±0.08
Change, Nm/kg 0.05±0.04 0.16±0.04* 0.06
Change, % 5.0±3 16.8±3* 0.02
Peak torque at 0°/s
Baseline, Nm/kg 1.19±0.08 0.97±0.07
Final, Nm/kg 1.24±0.08 0.20±0.07* 1.17±0.09
Change, Nm/kg 0.05±0.06 0.16
Change, % 6.7±7 24.5±8* 0.12
Sum of 0 and 60°/s peak torques
Baseline, Nm/kg 2.43±0.13 2.03±0.14
Final, Nm/kg 2.53±0.13 2.40±0.17
Change, Nm/kg 0.08±0.08 0.40±0.09* 0.02
Change, % 4.4±4 20.4±4* 0.02
====================================
Data are arithmetic means±SE except for change data
which are least
squares means±SE from the ANCOVA with baseline value and
percent change in
weight as covariates.
*P </=0.05 within group by ANCOVA with Tukey adjustment
for multiple
comparisons.

All indices of knee flexor strength relative to body weight
remained
unchanged
from baseline in the CR group and increased significantly in
the EX group
(Table 2 and
Figure 2). The changes in isokinetic flexion strength and
composite knee
flexion strength
were significantly different between groups. The changes in
isometric
flexion torque
were not significantly different between groups; however, it
is noteworthy
that the mean
values for these changes were similar to those seen for
isokinetic knee
flexion. When
strength data were reported relative to muscle volume, no
changes from
baseline were
evident in either study group and none of the between group
differences were
significant
(Table 3 and Figure 2).

Table 3. Isokinetic and isometric muscle specific torque
(torque ÷ thigh
muscle volume).
===========================================================
CR (n = 14) EX (n = 11) P (Between group)
===========================================================
Peak torque at 60°/s
Baseline, Nm/cm^3 0.128±0.007 0.106±0.008
Final, Nm/cm^3 0.127±0.006 0.109±0.007
Change, Nm/cm^3 0.002±0.003 -0.001 ±0.004 0.60
Change, % 2.43±2.8 1.30±3.2 0.81
Peak torque at 0°/s
Baseline, Nm/cm^3 0.121±0.008 0.098±0.007
Final, Nm/cm^3 0.122±0.008 0.103±0.008
Change, Nm/cm^3 0.003±0.006 0.002±0.007 0.92
Change, % 4.13±6.0 4.74±7.0 0.95
Sum of 0 and 60°/s peak torques
Baseline, Nm/cm^3 0.249±0.014 0.204±0.014
Final, Nm/cm^3 0.248±0.013 0.212±0.014
Change, Nm/cm^3 0.003±0.008 0.004±0.009 0.96
Change, % 1.82±3.4 3.11±3.9 0.82
===========================================================
Data are arithmetic means±SE except for change data
which are least
squares means±SE from the ANCOVA with baseline value and
percent change in
weight as covariates.
*P </=0.05 within group by ANCOVA with Tukey adjustment
for multiple
comparisons.
Data were calculated using right leg data for both
strength and muscle
volume.

Physiologic Responses to Maximal Treadmill Exercise. CR
resulted in a
decrease in absolute V . O2max; however, when expressed per
unit body weight
or lean
mass, no change in V . O2max was evident (Table 4). V .
O2max increased in
the EX group
regardless of whether it was expressed in absolute terms or
relative to body
weight or
lean mass. All of the changes in V . O2max, regardless of
how it was
expressed, were
significantly different between the CR and EX groups.

Table 4. Physiologic responses to maximal treadmill
exercise: V . O2max,
RER, VE/VO2, and heart rate.
===========================================================
CR (n = 15) EX (n = 14) P (Between group)
===========================================================
Absolute V^O(2)^max
Baseline, mL/min 2075±139 1965±158
Final, mL/min 1949±148 2250±175
Change, mL/min -133±46* 293±47* <0.0001
Change, % -6.8±2.315.5±2.4* <0.0001
V^O(2)^max relative to body weight
Baseline, mL/kg/min 26.3±1.2 25.5±1.4
Final, mL/kg/min 27.4±1.3 32.3±1.9
Change, mL/kg/min 0.9±0.7 7.0±0.7* <0.0001
Change, % 3.9±2.9 28.3±3.0* <0.0001
V^O(2)^max relative to lean mass
Baseline, mL/kg lean/min 43.5±1.2 40.5±1.2
Final, mL/kg lean/min 42.0±1.3 47.7±1.5
Change, mL/kg lean/min -1.5±0.9 7.2±0.9* <0.0001
Change, % -3.3±2.1 17.8±2.2* <0.0001
RER at maximal exercise
Baseline, mmHg 1.19±0.01 1.16±0.02
Final, mmHg 1.32±0.03 1.19±0.02
Change, mmHg 0.14±0.02* 0.03±0.02 0.001
Change, % 11.7±1.8* 2.49±1.8 0.002
VE/VO2 at maximal exercise
Baseline, mmHg 30.1±1.1 29.9±1.1
Final, mmHg 33.0±1.5 30.0±0.9
Change, mmHg 2.9±0.95* 0.17±0.99 0.06
Change, % 9.37±3.3* 2.09±3.4 0.13
HRmax
Baseline, mL/kg lean/min 170±2 173±3
Final, mL/kg lean/min 170±2 173±2
Change, mL/kg lean/min 0.34±1.5 0.92±1.5 0.79
Change, % 0.24±0.9 0.64±0.9 0.76
===========================================================
* P </=0.05 within group by ANCOVA with Tukey adjustment
for multiple
comparisons. Data are arithmetic means±SE except for change
data which are
least squares means±SE from the ANCOVA with baseline value
and percent
change in weight as covariates. V . O2max, maximal oxygen
uptake; HRmax,
maximal heart rate; RER, respiratory exchange ratio; VE/VO2
ventilatory
equivalent for oxygen uptake.

The high values for maximal exercise RER and VE/VO2 observed
during the
treadmill tests (Table 4) indicate that the subjects
achieved V . O2max.
Both RER and
VE/VO2 during maximal exercise increased in response to the
CR intervention
and the
increase in maximal exercise RER was significantly different
from that in
the EX group.
Although there was a tendency for the change in maximal
exercise VE/VO2 in
the CR
group to be different from that in the EX group, this
comparison did not
achieve
significance. HRmax did not change in either group and there
were no
between-group
differences (Table 4).
Oxygen pulse decreased significantly in the CR group and
increased
significantly
in the EX group and these changes were significantly
different between
groups (Table 5).
Systolic BP during maximal exercise was significantly lower
after the 1 yr
intervention in
the EX group only, whereas diastolic BP during maximal
exercise was
significantly
lower during the final test in the CR group only (Table 5).
The changes in
maximal
exercise systolic and diastolic BP were not different
between groups. RPP
during
maximal exercise did not change in either group and there
were no
differences between
groups (Table 5).

Table 5. Physiologic responses to maximal treadmill
exercise: oxygen pulse,
blood pressure, and rate pressure product.
===========================================================
CR (n = 15) EX (n = 14) P (Between group)
===========================================================
Oxygen pulse at maximal exercise
Baseline, mL/beat 12.2±0.8 11.3±0.9
Final, mL/beat 11.5±0.9 13.0±1.0
Change, mL/beat -0.82±0.3* 1.7±0.3* <0.0001
Change, % -7.2±2.5* 15.3±2.6* <0.0001
Systolic BP at maximal exercise^#
Baseline, mmHg 192±8.1 204±6.9
Final, mmHg 186±5.7 188±6.4
Change, mmHg -10.6±5.4 -12.2±5.4* 0.84
Change, % -4.44±2.4 -4.97±2.4* 0.88
Diastolic BP at maximal exercise^#
Baseline, mmHg 92±2.6 93±2.9
Final, mmHg 85±3.6 89±2.0
Change, mmHg -7.04±2.9* -3.74±2.9 0.44
Change, % -6.46±3.4 -3.43±3.4 0.53
RPP at maximal exercise^#
Baseline, mmHg 32740±1497 35243±1104
Final, mmHg 31692±1063 32620±1187
Change, mmHg -1749±974 -1922±974 0.90
Change, % -4.10±2.6 -4.65±2.6 0.88
=================================================
* P </=0.05 within group by ANCOVA with Tukey adjustment
for multiple
comparisons.
Data are arithmetic means±SE except for change data
which are least
squares means±SE from the ANCOVA with baseline value and
percent change in
weight as covariates.
^# Due to missing maximal exercise BP data, CR group
samples sizes for
maximal systolic BP, diastolic BP, and RPP are 1 less than
that listed in
table header.
BP, blood pressure; RPP, rate pressure product.

Seven subjects (1 CR, 6 EX) were taking BP medications for
hypertension
during
the study. While the medications and dosages for these
subjects did not
change during the
study, it is possible that the inclusion of these subjects
might have
affected the results of
the hemodynamic outcomes. Therefore, we performed several
sub-analyses after
excluding these subjects. Exclusion of the one subject who
was taking a
beta-blocker (EX
group) did not affect the HRmax or oxygen pulse results.
Exclusion of all
seven subjects
who were taking any BP medication did not alter the results
for maximal
exercise RPP or
maximal exercise diastolic BP; however, the significant
decrease in maximal
exercise
systolic BP for the EX group became non-significant (p=0.26).

DISCUSSION Results from the present study indicate that 12
months of
caloric restriction results
in significant reductions in absolute thigh muscle mass,
knee flexor
strength, and aerobic
capacity, while a similar yearlong energy deficit induced by
exercise
completely
preserves thigh muscle mass and strength and improvesV .
O2max. When
strength and
aerobic capacity are expressed relative to body weight,
there are no
decreases in response
to caloric restriction. However, in response to
exercise-induced weight
loss, there were
increases in body weight-related strength (17-24%) and
aerobic capacity
(28%), despite
the fact that the exercise regimens were designed primarily
for expending
energy, and not
necessarily for aerobic training or strengthening, per se.
Previous studies have demonstrated that a negative energy
balance induced by
caloric restriction results not only in loss of fat but also
in loss of
muscle (6, 7, 13, 14).
Although we did not measure total muscle mass in the present
study, it is
likely that both
caloric restriction and exercise-induced weight loss
resulted in net loss of
skeletal muscle
because lean mass measured by DXA (i.e. total body mass
minus fat and bone
mass)
decreased significantly in both groups. We measured thigh
muscle size as a
representative region of muscle that is involved in most
modes of endurance
exercise,
including those that were commonly used in the present
study. Thigh muscle
size
decreased in the caloric restriction group and was
completely preserved in
the exercise
group. It is likely that the changes in the caloric
restriction group were
due to loss of
contractile protein, as opposed to non-contractile
components of muscle such
as lipid and
connective tissue, because the decreases in size were
paralleled by
decreases in strength.
As a result, there were no changes in muscle specific torque
(i.e. torque
per unit muscle
volume). Taken together, these findings suggest that
endurance exercise
protects against
the energy deficit-induced loss of skeletal muscle size and
strength,
although it is likely
that this is only true for muscles that are active during
exercise.
Dietary protein consumption may affect the amount of lean or
muscle mass
that is
lost during caloric restriction-induced weight loss (2, 9).
As a consequence
of the reduced
food consumption in the caloric restriction group, there was
a marginally
significant
decrease in absolute daily protein consumption. In contrast,
absolute daily
protein
consumption in the exercise group remained unchanged.
However, as a result
of the
decreases in body weight in both groups, protein consumption
relative to
body weight
was unchanged in the caloric restriction group and increased
in the exercise
group. It is
possible that the differences in protein consumption between
the caloric
restriction and
exercise groups might have been partly responsible for the
differential
effects of the
weight-loss interventions on muscle size and strength.
Absolute aerobic capacity decreased in response to caloric
restriction in
the
present study. BecauseV . O2max is the product of HRmax,
maximal exercise
stroke
volume (SVmax), and maximal exercise arteriovenous oxygen
content difference
(aV^O(2)^max),
and because HRmax did not change during the intervention,
the decrease in
V^O(2)^max was due to decreases in SVmax and/or
a-V^O(2)^max. In contrast to
what was
observed in the caloric restriction group, the energy
deficit induced by
exercise resulted
in increases in aerobic capacity and oxygen pulse. Previous
studies have
shown that
V^O(2)^max increases in response to exercise training
through increases in
SVmax and aV^O(2)^max
(17, 18). To a large extent, the increases in SVmax are due
to physiologic
hypertrophy of the myocardium (11, 16) and the increases in
a-V^O(2)^max are
due to
increases in the capillary density and mitochondrial content
in skeletal
muscle (1).
Therefore, despite the presence of a whole-body catabolic
state (i.e. weight
loss), exercise
may have had adaptive effects on skeletal muscle
mitochondria and the
myocardium.
However, we do not have direct evidence to support this notion.
Interpretation of the body weight-independent data from the
present study
would
suggest that caloric restriction has adverse effects on
strength and
cardiovascular fitness
and that this might decrease the capacity for physical
performance. It is
important to note,
however, that because caloric restriction resulted in
substantial weight
loss, the absolute
work requirement for many (but not all) common activities
such as climbing
stairs, also
decreased. Therefore, from this perspective, the decreases
in strength and
aerobic
capacity are proportional to the reduction in body weight
and the capacity
for weight
bearing exercise (i.e. walking, running, climbing) would not
likely be
impaired. In the
same context, however, it should also be recognized that
weight loss induced
by exercise
coincided with a preservation of absolute strength and an
increase in
absolute aerobic
capacity and therefore likely increased the capacity for
physical
performance.
The present study has strengths and limitations. One of the
strengths is our
measurement methods; we used a strict treadmill protocol to
assess "true"
V^O(2)^max and
we used volumetric MRI-based measurements for thigh muscle
size. Another
strength is
that we did not exclude data from subjects who were
non-compliant with the
intervention
protocols; the data, therefore, reflect the average
responses of overweight,
middle-aged
men and women to these interventions, rather than the
best-case scenario for
fully
compliant individuals. A weakness of our study is that our
strength
assessments were
limited to the knee flexor muscles and we cannot, therefore,
conclude about
the effects of
these interventions on strength in other regions of the
body. Furthermore,
because the
muscle specific torque data were based on all muscles in the
thigh, rather
than the knee
flexors alone, and because we did not consider the
biomechanical aspects of
knee flexor
force transfer, our data are only an index of muscle
specific torque and not
a direct
measure of force generation per unit of muscle tissue.
Another limitation is
that this was
a fairly intensive intervention that required the
participants to visit our
facility on a
weekly basis for weight checks and consultation. Therefore,
data from the
present study
cannot be used to deduce the benefits of less supervised
caloric restriction
and exercise
interventions. Finally, because we did not include a
combined caloric
restriction and
exercise intervention, which might be more practical to
perform, we cannot
determine if
the beneficial effects of exercise override the effects of
caloric
restriction on absolute
aerobic capacity, muscle size, and muscle strength.
In summary, data from the present study provide evidence
that caloric
restriction
results in reductions in muscle size and strength and in
aerobic capacity,
although these
changes are proportional to the reduction in body weight. In
contrast,
similar weight loss
induced by increasing exercise energy expenditure without
changes in energy
intake
prevents the loss of muscle size and strength, at least in
the exercised
muscles, and
increases aerobic capacity. Data from the exercise group in
the present
study suggest that
in the presence of an overall negative energy balance, the
body is capable
of selectively
preserving and/or synthesizing skeletal muscle and perhaps
other tissues
that are involved
in oxygen uptake and, thus, maintaining the capacity for the
performance of
physical
activity.