Energy yield from carbohydrate, fat, and protein during physical activity is partially dependent on an individual's fitness level. Prolonged exposure to microgravity causes musculoskeletal and cardiovascular deconditioning; these adaptations may alter fuel utilization during space flight. Carbohydrate and fat metabolism during exercise were analyzed before and after 7 days of horizontal bed rest

Barrows, Linda H.

Harris, Bernard A.

Moore, Alan D.

Siconolfi, Steven F.

English

NASA Technical Reports Server

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Fuel Utilization
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After 7Days
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Bernard A. Harris,
Alan D. Moore, -__
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https://ntrs.nasa.gov/search.jsp?R=19920007336 2020-03-17T12:55:38+00:00Z

NASA
Technical
Paper
3175
1992
National Aeronautics and
Space Administration
Office of Management
Scientific and Technical
Information Program
Fuel Utilization
During Exercise
After 7 Days
of Bed Rest
Linda H. Barrows
I_UG Life Sciences
Houston, Texas
Bernard A. Harris
Lyndon B. Johnson Space Center
Houston, Texas
Alan D. Moore
KRUG Life Sciences
Houston, Texas
Steven F. Siconolfi
Lyndon B. Johnson Space Center
Houston, Texas

INTRODUCTION
Fuel utilization during exercise is affected by an individual's state of
physical conditioning. Coyle [1] has shown reduced oxidative
(aerobic) enzyme levels and increased glycolytic (anaerobic) enzyme
levels after detraining. The decrease in oxidative enzyme activity
seen with detraining suggests a lowered ability to use fat as a fuel
source during exercise, while increased glycolytic enzyme levels
would indicate a greater reliance on carbohydrate for energy
metabolism.
Bed rest is a model used to simulate exposure to a microgravity
environment. The deconditioning incurred after prolonged periods of
bed rest is of equal or greater magnitude than that seen with classic
detraining. Prolonged bed rest has been shown to decrease several
performance variables, including maximal and submaximal oxygen
uptakes [2, 3, 4, 5, 6], and skeletal muscle performance [7, 8, 9]. The
decrease in these factors may be associated with altered energy
metabolism.
Respiratory quotient (RQ), or the respiratory exchange ratio, has been
used to indicate substrate utilization (percent of calories from fat and
carbohydrate, ignoring protein contribution) during exercise. Post-
bed rest elevations in RQ have been reported during submaximal [4,
10, 11] and maximal exercise [5]. These elevated RQ values post-bed
rest may be indicative of a greater reliance on carbohydrate for
energy during exercise and earlier onset of increased anaerobic
metabolism.
Several studies support the hypothesis of greater reliance on
anaerobic energy pathways during graded exercise after imposed
deconditioning. Increased concentrations of blood lactate and
decreased levels of total circulating free fatty acids were found
during submaximal bicycle ergometry following ten days of -6 °
head-down tilt bed rest [10]. Coyle [1] reported a40% decrease in
mitochondrial enzyme activity levels and a change in total lactate
dehydrogenase activity after 56 days of detraining in seven
endurance athletes. These studies suggest that, with prolonged
disuse, there is a decrease in aerobic metabolism and an increase in
carbohydrate utilization during exercise.
Evidence of a reduced aerobic capacity, as shown by bed rest, has
significant implication for the physical performance of crewmembers
during space flight. Crewmembers are often required to perform
demanding tasks during space flight, such as extravehicular activity
(EVA), under less than optimal conditions for maintaining
performance. In addition, pilot proficiency during entry and landing,
and performance of nominal and/or emergency egress pose real
concerns for Extended Duration Orbiter (EDO) space flight (missions
exceeding 13 days) and emphasize the need to minimize decrements
in aerobic capacity. The following study was designed to evaluate
changes in fat and carbohydrate metabolism, indicators of energy
pathways used for ATP synthesis, during exercise performed after
seven days of simulated microgravity.
METHODS
Subjects were recruited through the Health Screening Facility at the
NASA Johnson Space Center and required to pass a screening
examination similar to an Air Force Class III physical prior to
commencing the study. Eight male subjects [(mean + SD)age, 34.4
+ 4.1 yr; height, 177.8 + 8.5 cm; weight, 83.7 + 12.6 kg; body fat, 15.9
+ 7.3%] were selected for this study based on having similar
morphological characteristics to those of the current male astronaut
corps. All subjects were nonsmokers, not taking any prescription
medications at the time of the study, and reported no orthopedic
limitations. Subjects gave written informed consent to participate in
this study.
Consumption of a liquid diet (ENSURE and ENRICH, Ross Laboratories,
Columbus, OH; mean kcal/kg/day = 28.9 + 2.8) began three days prior
to bed rest and was designed to maintain subjects' weight at
+ 1% of their pre-bed rest body weight. Consumption of a liquid diet
continued through the second day after bed rest. Bed rest consisted
of seven days in the horizontal position (0 ° head-down tilt) during
which subjects remained completely supine with arms as close to
their sides as possible.
Two treadmill familiarization trials were completed prior to the start
of data collection. Graded exercise testing was conducted on a
continuous, motor-driven treadmill (Quinton Model 65, Quinton
Instruments, Seattle, WA) in the Exercise Physiology Laboratory at
the Johnson Space Center. Testing was carried out once two days
pre-bed rest (GXT1) and again immediately post-bed rest (GXT2),
within hours of assuming an upright position. A modified
Cunningham treadmill protocol [12] was utilized to assess energy
2
metabolism. This protocol increased treadmill speed every three
minutes from 3.5 mph to 4.0, 4.5, 5.0, 6.0, and then 7.0 mph. Once a
speed of 7.0 mph was attained, treadmill grade increased by 2.5%
every minute thereafter until subjects attained a plateau in VO2
response (an increase of less than 100 mL/min with increasing
workload) or indicated volitional fatigue.
A 12-lead electrocardiogram (Quinton 4000), asculatory blood
pressure, and ratings of perceived exertion [13] were obtained
during each stage of exercise. Expired gas was analyzed by a
Marquette MGA 1100 Mass Spectrometer (Marquette Gas Analysis
Inc., St. Louis, MO), with a SensorMedics VMM2 turbine flow meter
(Alpha Technologies Inc., Laguna Hills, CA). Respiratory parameters
were computed using breath-by-breath software (First Breath Inc.,
Ontario, Canada).
Percentage of calories derived from fat (%FAT) and carbohydrate
(%CHO), and grams of fat (gFAT) and carbohydrate (gCHO) utilized in
four submaximal stages of treadmill exercise, ranging from 4-6 mph,
(4.7-10.1 Metabolic Equivalents, METS) were computed from $'02 and
_/CO2 values obtained during the last 30 seconds of each three-
minute stage. Grams of fat and carbohydrate burned were computed
utilizing the following equations in which units of VO2 and VCO2 are
measured in L/min [14]:
Grams of FAT: [VO2- VCO2]/0.570
Grams of CHO: [4.2144oVCO2- 3.007.VO2]
A 2x4 repeated measures ANOVA with Newman-Kuels post hoc test
was used to analyze carbohydrate and fat metabolism during
submaximal exercise performed pre- and post-bed rest.
RESULTS
There were no significant (p>0.05) differences in mean weight or
percent body fat (hydrostatic weighing) pre- and post-bed rest.
There was, however, a significant (p<0.05) decrease in absolute
aerobic capacity after seven days of bed rest, measured in GXT1 and
GXT2 (Table I).
3
TABLE I. Post-bed rest subject characteristics (n = 8) compared to
pre-bed rest (mean + SD).
Weight (kg)
Body fat (%)
VO2max (mL/min)
*(p<0.05)
Pr¢-Bed Rest
83.7 + 12.6
15.9 + 7.3
3638.8 + 548
Po_t-Bed Rest
81.6 + 1 1.6
16.1 + 7.4
3454.9 + 523"
In both GXTI and GXT2, there was a significant (p<0.05) increase in
carbohydrate use as exercise intensity increased, while fat utilization
significantly (p<0.05) decreased with increasing workloads. There
were no significant (p>0.05) differences in %CHO, %FAT or gFAT in
comparable submaximal stages of GXTI and GXT2 (Table II, Figures 1,
2, 4). There was, however, a significant (p<0.05) increase in gCHO
from GXT1 to GXT2 at stages of exercise corresponding to 8.1 and 10.1
METS (Table II, Figure 3).
TABLE II. Summary of carbohydrate and fat utilization for GXT1 and
GXT2 (mean + SD). (mph = 0.62 km/hr)
Stage 2 Stage 3 Stage 4 Stage 5
(4.5 mph) (5.0 mph) (6.0 mph)
°/K]D
GXT1 74.0 ± 35.1 79.3 + 44.4 84.9 + 21.7 91.9 + 29.6
GXT2 68.9 + 20.4 88.5 + 23.1 100.1 + 14.7 105.2 + 18.3
%FAT
GXT1 26.0 + 35.1 20.7 + 44.4 5.1 + 21.7 8.1 + 29.6
GXT2 31.2 + 20.4 11.5 + 23.1 -0.08 + 14.7 -5.2 + 18.3
gCHO
GXT1 1.7 + 0.96 2.4 ± 1.2 2.6 + 0.73* 3.3 + 0.89*
GXT2 1.6 + 0.56 2.6 + 0.72 3.1 + 0.47 3.8 + 0.7
gFAT
GXT1 0.26 + 0.34 0.14 + 0.36 0.21 + 0.29 0.07 + 0.35
GXT2 0.34 + 0.18 0.11 + 0.21 0.03 + 0.18 -0.1 + 0.22
*GXT2 > GXT1, p <0.05
4
140.
120 -
100-
40.
[] GXTI
[] GX_
IL
o
4.7
Figure 1
80'
70,
60,
50,
40,
I0.
0
-10'
-30
6.4 8.1 10.1
Mm'S
1
4_7 6_4 8_I |0,I
IVIETS
%Calories from
Carbohydrate
Figure 2 - %Calories from Fat
5,
m c_xr2
4 *_'0.05
3
2
l
0 ,
4.7
Figure 3
6.4 8.1
METS
I0.I
Grams of Carbohydrate
Burned
0.8
0.7
0.6
0.5
0.4
0.3-
0.2-
0.1.
0.0
-0.1.
.-11.2-
-0.3-
-0.4
m _x'r2
4.7 6.4 8.1 1 ,1
METS
Figure 4 - Grams of Fat Burned
CONCLUSION
Results of this study suggest an increased rate of carbohydrate
utilization during submaximal exercise after seven days of horizontal
bed rest. This finding was more evident when carbohydrate
utilization was expressed in grams rather than when expressed as a
percentage of total calories burned during exercise. Therefore, fuel
utilization during exercise, expressed as a percentage of total exercise
caloric cost, may not be a sensitive measure of energy metabolism.
An increased rate of carbohydrate metabolism during exercise after
bed rest suggests that the efficiency of aerobic energy metabolism
decreased, similar to that seen with detraining, with a trend toward
earlier onset of anaerobic metabolism. This earlier onset supports
the findings of previous investigations in which higher
RQs were seen during exercise after periods of bed rest, also
indicative of anaerobic metabolism [4, 10, 11].
A shift in fuel utilization during extended duration spaceflight may
prove deleterious to performance of mission tasks. A greater
reliance on anaerobic energy metabolism could result in glucose
depletion with prolonged activity, lactic acid accumulation, and
forced, premature termination of a planned activity. Exercise
countermeasures need to be designed to minimize space flight
induced deconditioning and, therefore, maximize aerobic pathways
for energy derivation.
6
REFERENCES
1. Coyle, E. F., Martin, W. H., Bloomfield, S. A., Lowry, O. H., and
Holloszy, J. O. Effects of detraining on responses to submaximal
exercise. J. Appl. Physiol. 59(3):853-859, 1985.
2. Nicogossian, A. E., Huntoon, C. L., and Pool, S. L. Space
Physiology and Medicine, 2nd Ed. Philadelphia, PA, Lea & Febiger,
1989.
3. Greenleaf, J. E., Wade, C. E., and Leftheriotis, G. Orthostatic
responses following 30-day bed rest deconditioning with isotonic and
isokinetic exercise training. Aviat. Space Environ. Med. 60:537-542,
1989.
4. Convertino, V. A., Goldwater, D. J., and Sandier, H. Bed rest-
induced peak VO2 reduction associated with age, gender, and aerobic
capacity. Aviat. Space Environ. Med. 57:17-22, 1986.
5. Convertino, V. A., Hung, J., Goldwater, D., & DeBusk, R. F.
Cardiovascular responses to exercise in middle-aged men after 10
days of bed rest. Circulation 65(1):134-140, 1982.
6. Convertino, V. A., Sandler, H., Webb, P., and Annis, J.F. Induced
venous pooling and cardiorespiratory responses to exercise after bed
rest. J. Appl. Physiol.: Respirat. Environ. Exercise Physiol.
52(5):1343-1348, 1982.
7. Dudley, G. A., Gollnick, P. D., Convertino, V. A., and Buchanan, P.
Changes of muscle function and size with bed rest. The Physiologist
32(1):565-566, 1989.
8. LeBlanc, A., Gogia, P., Schneider, V., Krebs, J., Schonfeld, E., and
Evans, H. Calf muscle area and strength changes after five weeks of
horizontal bed rest. Am. J. Sports Med. 16(6):624-629, 1988.
9. Greenleaf, J. E., Van Beaumont, W., Convertino, V. A., and Starr,
J.C. Handgrip and general muscular strength and endurance during
prolonged bed rest with isometric and isotonic leg exercise training.
Aviat. Space Environ. Med. 54(8):696-700, 1983.
10. Williams, D. A. and Convertino, V. A. Circulating lactate and
FFA during exercise: Effect of reduction in plasma volume following
7
exposure to simulated microgravity.
59:1042-1046, 1988.
Aviat. Space Environ. Med.
11. Convertino, V. A., Goldwater, D. J., and Sandler, H. _O2 kinetics
of constant-load exercise following bed rest-induced deconditioning.
J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 57(5):1545-
1550, 1984.
12. Cunningham, L. N. Physiologic characteristics and team
performance of female high school runners. Pediatric Exercise
Science 1:73-79, 1989.
13. Borg, G. A. A category scale with ratio properties for
intermodal and interindividual comparisons. In: Proceedings of the
22nd International Congress of Psychology. Leipzig: Deutscher
Verlag, 1980.
14. Karpovich, P. V. and Sinning, W. E. (eds.) Physiology of Muscular
Activity, 7th Ed. Philadelphia: W. B. Saunders Company, 1971.
8
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t 3.REPORTTYPEAND DATESCOVEREDTechnical PaperJanuary 1992
Exercise After 7 Days of Bed Rest
6. AUTHOR(S)
Linda H. Barrows, Bernard A.
and Steven F. Siconolfi
Harris, Alan D. Moore,
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National Aeronautics and Space Administration
Johnson Space Center
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L. H. Barrows and A. D. Moore (KRUG Life Sciences, Houston, Texas)
B. A. Harris and S. F. Siconolfi (NASA Johnson Space Center, Houston, Texas)
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13. ABSTRACT (Maximum 200 words)
Energy yield from carbohydrate, fat and protein during physical activity is partially
dependent on an individual's fitness level. Prolonged exposure to microgravity causes
musculoskeletal and cardiovascular deconditioning; these adaptations may alter Fuel
utilization during space flight. Carbohydrate and fat metabolism during exercise were
analyzed in this study before and after 7 days of horizontal bed rest.
14. SUBJECT TERMS
Energy yield,
utilization,
f_tness level, cardiovascular deconditfonlng, fuel
and carbohydrate and fat metabolism
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Fuel utilization during exercise after 7 days of bed rest

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