TISSUE AND CELL, 1992 24 (4) 491-498 0 1992 Longman Group UK Ltd.

L. C. MAXWELL*,

C. S. ENWEMEKAt and G. FER,NANDESS

EFFECTS OF EXERCISE AND FOOD RESTR ICTION ON RAT SKELETAL MUSCLES Keywords: Muscle, rat, fiber type, exercise, food restriction ABSTRACT. Studies were undertaken to compare the effects of exercise and food restriction on body weight (BW), muscle weight (MW), muscle fiber size, and proportion of muscle fiber types. 20 male Fischer 344 rats were randomly assigned to four equal groups: ad lib&urn-fed control (AC), ad libitum-fed exercise (AE), food restricted control (RC) and food restricted exercise (RE). From 6 weeks of age, RC and RE rats received 60% of the daily food intake of AC and AE rats, respectively. At 7 months of age, AE and RE rats began 4C-50 min of daily treadmill exercise. Running speed increased from 1.2 to 1.6 miles/hour and the grade increased to 15% during the first 2 weeks of training. After 10 weeks of training, rats were weighed, sacrificed, and the soleus (SOL), plantaris (PLN) and extensor digitorum longus (EDL) muscles were removed at in situ rest length, weighed, and quick-frozen. Standard histochemical assays were performed, and muscle fiber cross-sectional area was determined planimetrically. Training had little effect on MW or BW, but food restriction greatly reduced BW. This resulted in greater MW/BW ratio in RC and RE than AC and AE rats, respectively. Exercise also increased SOL muscle fiber area in ad lib&urn-fed but not food restricted rats resulting in smaller fibers in SOL of RE than AE. No changes in percentage of SOL fiber types occurred with food restriction or exercise. In PLN, the percentage of fast-twitch oxidative fibers of AE and RE was greater than in AC and RC, but there was no effect of food restriction or exercise on fiber area. Neither food restriction nor exercise altered the percentages of fiber ‘types in EDL, but fast-twitch fibers in RE were smaller than in AE. We conclude that food restriction does not alter fiber type percentages or reduce fiber area in sedentary rats; nor does it prevent fiber type conversion in response to endurance training. However, fibers in SOL and EDL muscles of RE were smaller than AE, indicating that food restriction prevents exercise induced muscle hypertrophy.

Maxwell et al., 1973). Training of limb skeletal muscles is possible in young and old guinea pigs (Lieberman et al., 1972; Maxwell et al., 1973) and rats (Beyer et al., 1984; Daw et al. , 1988), and is an effective way to reverse or retard age-related decline in oxidative capacity (Beyer et al., 1984) or muscle mass (Daw et al., 1988) of affected muscles. Endurance training improves survival, but does not increase longevity in rats (Holloszy et al., 1991). Life-long restriction of caloric intake in Fischer 344 rats has been well-documented as an effective means of extending the life span (Masoro, 1989) and reducing pathological changes associated with aging (Maeda et al., 1985). There are several mechanisms by which food restriction may protect muscle tissue from age-related decrement in function: (a) by preventing pathological

Introduction Endurance exercise, e.g. treadmill is a potent stimulus for adaptation muscle fiber oxidative capacity.

running, of skeletal

Compared to sedentary animals, muscles of endurance trained animals hnve up to twice the capacity to perform oxidative metabolism (Holloszy, 1975; 1984), and this correlates with increased percentage of oxidative fibers in trained muscles (Barnard et al., 1971; *Departments of Physiology and *Medicine, and Division of tPhysicaI Therapy, University of Texas Health Science Center, 7703 Floyd Curl Drive, San Antonio, TX 78284-7756, USA and Department of Orthopaedics and tRehabilitation Division of Physical Therapy, University of Miami School of Medicine, and Research Service, Veterans Affairs Medical Center, Miami, FL, USA. Correspondence to: Dr. Leo C. Maxwell. Received 21 January 1992. 491

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changes in other tissues (Maeda et al., 1985), muscle functional capability could be maintained in healthier, more active animals (Yu et al., 1985), (b) by reducing carbohydrate intake irreversible glycation of cellular constituents (Cerami, 1985; Masoro et al., 1989), (c) by retarding the age-related loss of free radical detoxifying ability (Yu et al., 1988; Laganiere and Yu, 1989), muscle could be preserved from damaging effects of free radical metabolism, and (d) by maintaining a higher level of spontaneous exercise activity (Yu et al., 1985), loss of skeletal muscle functional capacity with age may be delayed. Muscle weight, fiber cross-sectional area, and contractile properties are relatively unaffected by short term (90 hr) nutritional deprivation to one-third of normal food intake (Kelsen et al., 1985; Lewis and Sieck, 1990), but 4 days of complete starvation leads to functional decline in diaphragm muscle strength (Dureuil et al., 1989). Nutritional deprivation (one-third of normal food intake) for 4 weeks causes reduced oxidative enzyme activity and muscle fiber atrophy (Sieck et al., 1989). Long term (initiated at 3 months of age) food restriction to 65-70% of ad libitum food intake in Fischer 344 rats reduced muscle mass at 12 months of age, but had no significant effect upon muscle mass or fiber number of soleus or extensor digitorum longus muscles of 27-month-old animals (Daw et al., 1988). Similarly, McCarter and McGee (1987), found that food restriction (60% of ad libitum food intake) initiated at 6 weeks or 6 months of age in Fischer 344 rats had little functional change and only minor changes in collagen content, DNA concentration, protein concentration, or the ratio of dry muscle weight to wet muscle weight in soleus or omohyoideus muscles. However, others have found that acute starvation induces up to 40% decrease in muscle pyruvate dehydrogenase activity within 1.5hr (Holness et al., 1989). This effect can be reversed within 4-6 hr of refeeding (Sugden and Holness, 1989). Chronic food restriction (50% of ad libitum food intake) is reported to cause a significant retardation of growth and development, and a decrease in protein turnover in diaphragm and limb skeletal muscles of rats (el Haj et al., 1986; Goldspink et al., 1987), or a decrease of fiber number in extensor digitorum longus muscles of rats (Bore-

ET AL.

ham et al., 1988). Conflicting data on the effect of age or food restriction may be related to studies of barrier-raised vs nonbarrier-raised rats (McCarter, 1990), and it appears that food restriction in healthy barrier raised rats is not deleterious to muscle. Food restriction in combination with some diseases may be deleterious to human muscle (Edelman et al., 1986). It is becoming common for individuals to participate in endurance training and dietary restriction programs simultaneously. In rats, food restriction increases the longevity of sedentary or endurance trained animals, but food restriction may adversely affect survival of young to middle aged training animals (Holloszy et al., 1991). Despite the beneficial effects of endurance training on survival and of food restriction on longevity, the combined effects of exercise and food restriction on adaptation of muscle tissue remain poorly understood. It is conceivable that exercise combined with food restriction interactively alter age-related decline of skeletal muscles. The purpose of our study was to determine the effects of food restriction and endurance exercise on the soleus, plantaris, and extensor digitorum longus muscles of adult male Fischer 344 rats. Our specific aims were to determine the effects of (1) food restriction, (2) endurance training, and (3) a combination of food restriction and endurance training on muscle weight, muscle fiber crosssectional area, and the proportions of Types I, IIc, 110, and IIg fibers in soleus, plantaris and extensor digitorum longus muscles.

Methods Experimental

design: A total of 20 male Fischer 344 rats (Charles River Laboratory, Wilmington, MA) were studied. These were maintained individually in plastic cages in light and temperature controlled limited access barrier facilities since 6 weeks of age. Rats were allowed water ad libitum and were either allowed ad libitum access to food, or were restricted to 60% of the normal ad libitum food intake as previously described (Laganiere and Fernandes, 1991). The diet was a commercially prepared pelleted food (Ralston-Purina, St. Louis, MO) comprised of 58% carbohydrate (314 dextrin, l/4 sucrose), 22% fat (corn oil), and 20% protein

EFFECTS OF EXERCISE

AND FOOD RESTRICTION

(casein). Vitamin content was adjusted to deliver the same vitamin dose to ad libitum fed and food restricted rats. Five animals each were assigned to ad libitum sedentary control (AC), ad libitum fed endurance trained (AE), food restricted sedentary control (RC) or food restricted endurance trained (RE) groups. Veterinary care included operation of the barrier facility and regular monitoring of the animals for serum viral and mycoplasma antibodies. Endurance

training: Endurance trained animals were subjected to 40-50 minutes of treadmill running daily for ten weeks, beginning at 7 months of age. The treadmill grade was increased to 15% and the treadmill speed to 1.6 miles per hour during the first two weeks of the training protocol. Muscle

samples. Rats were weighed and anesthetized by ether inhalation. The soleus (SOL), a slow twitch muscle, plantaris (PLN) and extensor digitorum longus (EDL), predominantly fast twitch muscles, of one limb were exposed by skin incision. The knee and ankle joints were held in neutral position, the muscle tendons were tied to preweighed wooden splints in situ. Muscles were removed by severing tendons and other connections, weighed, and quick frozen by immersion in isopentane cooled to its freezing point with liquid nitrogen. Histochemical analysis. The frozen muscles were equilibrated to the cryostat temperature (-2o”C), and a 3-4 mm thick slice was cut from the midbelly perpendicular to the long axis of the muscle. The remaining portions of each muscle were weighed wet and oven dried to constant weight for determination of water content. The frozen slice was mounted on a cryostat chuck and 10pm cross-sections cut. Following 30 to 60 min room temperature air drying of the crossanalyses were persections, enzymatic formed. Enzymatic reactions for myofibrillar ATPase, performed after alkaline or acid preincubation were used as correlates of contractile velocity (Dubowitz and Brooke, 1973). Fibers were classified as Type I or Type II based on low or high ATPase activity, respectively, after alkaline preincubation. Type II muscle fibers which did not demonstrate a reversal in ATPase activity fol-

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lowing acid preincubation were labeled Type 11~. The remaining Type II fibers were classified Type 110 or Type IIg based on high or low oxidative capacity as indicated by the activity of reduced nicotinamide adenine dinucleotide tetrazoleum reductase (NADHTR). Following completion of enzymatic reactions, sections were dehydrated in an ascending series of ethanol (70%) 95%, and lOO%), cleared in xylene and mounted with Permount. Muscle sections were observed with a Zeiss microscope equipped with a drawing tube that allows tracing of a magnified image of individual muscle fibers. Three regions of each muscle were randomly chosen for drawing within a standardized rectangular sample area. Fibers crossing the top and right edges of the rectangle including the top left corner were included in the drawings while those crossing the left and bottom edges and bottom right corner were excluded. More than 100 fibers were drawn for each muscle. The fiber type composition of each muscle was determined by counting the number of fibers of each type in the sample area. The cross sectional area of each fiber was measured from the drawings using a Bioquant digitizer. The mean fiber area for each fiber type of each muscle sample was calculated. Statistical analysis.

Data was pooled for each group and the mean, standard deviation and standard error of the mean’calculated. Data are presented as mean + standard error. Analysis of variance and Student Neuman Kuehl tests were used to compare the fiber area and percentages of fiber types in muscles of experimental groups to controls, while an unpaired student t-test was performed to compare groups. All statistical procedures were performed as described by Zar (1974).

Results Body

weight:

Mean body weight of food restricted rats was less than that of ad libitum fed rats in both control (261 k 4 and 389 -t 7 grams, for groups RC and AC, respectively) and exercise animals (268 -C4 and 383 -C 11 for groups RE and AE, respectively) (Fig. 1). There was no significant effect of exercise on body weight in either food restricted or exercised rats.

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z

E E 9 E .P g

AC

AE

RC

RE

Group Fig. 1. Final body weight (grams) is shown for adlibitum fed sedentary (AC), ad libitum fed exercised (AE), food restricted sedentary (RC) and food restricted exercised (RE) rats.

weight: Food restriction caused reduction of soleus (SOL), plantaris (PLN) and extensor digitorum longus (EDL) muscle weight (Table 1). This result reached significance at the p < 0.05 level for food restricted vs ad libitum fed sedentary control or exercised animals except for PLN of RE compared to AE. Normalizing data for differences in body weight showed significant increase in muscle weight to body weight ratios for food restricted vs ad libitum fed control and exercised animals. This effect was significant (p < 0.05) for all but PLN of RC vs AC. Endurance exercise had no significant effect upon muscle weight or muscle weight to body weight ratio in either food restricted or ad libitum fed animals. Fiber area: Endurance

exercise significantly increased mean fiber cross-sectional area (MFCSA) for SOL of ad libitum fed animals

Table 1. Muscle weight and muscle weight: body weight ratio

Group AC AE RC RE

SOL 140 f 155 + 117 k 130 t

Muscle weight (mg) PLN EDL 7 7 5* 4*

353 f 333 f 279 + 294 2

13 43 13* 12

152 f 157 t 136 * 134 2

Muscle weight/body weight (g/Kg x 10m6) SOL PLN EDL 3 3 6* 7%

360213 412 + 32 450 f 25* 486 + 13*

908 ‘- 26 860 + 98 1072 ” 57 1098 2 35*

394 +. 5 410 k 13 524 2 22* 500 +- 11*

AC: Ad-libitum fed sedentary control, AE: Ad-libitum fed exercised, RC: Food restricted sedentary control, RE: Food restricted excised. * RE significantly different from RC or AE significantly different from AC (p < 0.05).

Table 2. Mean fiber cross-sectional area (pm’) of soleus, plantaris and extensor digitorum longas muscles SOL AC AE RC RE

2878 + 30 3621 k 349* 2685 -r- 112 3270 + 211

EDL

PLN 2788 2 2998 2 2500 2 2906 2

75 234 157 261

1961 k 153 2155 2 141 1740 r 133 1660 -c 71t

AC: Ad-libitum fed sedentary control, AE: Adlibitum fed exercised, RC: Food restricted sedentary control, RE: Food restricted exercised. * AE significantly different from AC (p < 0.05). t RE significantly different from AE (p < 0.05).

(Table 2). Although MFCSA also increased with endurance exercise in food restricted animals, this increase did not reach statistical significance. Food restriction alone had no significant influence on SOL muscle MFCSA. Neither food restriction nor endurance exercise had significant effect on MFCSA of PLN muscles. A slight increase in MFCSA in EDL muscles of ad libitum fed animals and a slight decrease in MFCSA in EDL of food restricted animals resulted in significantly smaller MFCSA in EDL muscles of endurance exercised compared to sedentary food restricted rats.

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OF EXERCISE

AND FOOD

RESTRICTION

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and IIg fibers of food restricted exercised animals were significantly smaller. Percentage offiber types: Endurance

exercise significantly increased the percentage of Type 110 fibers in PLN of ad-libitum fed and food restricted rats (Fig. 3). However. endurance exercise had no effect on the percentage of fiber types in SOL or EDL muscles, nor did food restriction have a significant effect on the distribution of fiber types in SOL, PLN or EDL muscles.

Group

q

4500 “E 2

q IMFA q IlcMFA q Ilo MFA q Ilg MFA

4000 3500

m 3000 $

2500

b

2000

SOI FUS f-J % I

AC

a 2

AE

q%

IIC

q%

II0

0

0

RC RE 0

FXTFNSOR D~G~TOIWMI ONGUS

20

40 Percent

60 60 of Fibers

100

4500 “E 2

4000

PLANTARIS

3500

m 3000 $

2500

z

2000

f

1500

6

1000

9

500

AC

0

+REvSAE (““I

AC

AE

RC

RE

Group

Fig. 2. Mean fiber area (pm*) of Type I, Ilc, 110, and IIg fibers are shown for SOL, PLN and EDL muscles of ad libitum fed sedentary (AC), ad libitum fed exercised (AE), food restricted sedentary (RC) and food restricted exercised (RE) rats.

Mean fiber area of Type I, Type IIc, and 110 fibers of SOL muscles of ad libitum fed rats increased significantly in response to endurance training (Fig. 2). Compared to ad libitum fed exercised animals, SOL Type I fibers of food restricted exercised animals were not significantly smaller, but Type IIc and 110 fibers were. No significant effects of food restriction or exercise were observed on PLN muscle fiber areas. Compared to ad lib&m fed exercised animals, EDL Type 110

RE 0

20

40 Percent

60 60 of Fibers

100

FXTFNSOR DlGlTOFi&I I ONGUS

K.,...,..., 0 20

40 Percent

. . . 60 60 of Fibers

100

Fig. 3. Percentage of Type I, 11~. 110. and IIg fibers are shown for SOL, PLN, and EDL muscles of ad libitum fed sedentary (AC), ad libirum fed exercised (AE), food restricted sedentary (RC) and food restricted exercised (RE) rats.

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Discussion Body weight of the barrier-raised ad libitum fed Fischer 344 rats was 38&390 grams. These values for rats of approximately 9.5 months of age slightly exceed the value previously reported by Eddinger et al. (1985) for 8.8-month-old rats and are less than the values reported by Daw et al. (1988) for 12month-old rats. Food restriction to 60% of normal ad libitum caloric intake led to reduction of body weight to less than 70% of the body weight of ad libitum fed animals. This compares to a reduction to 71% of ad libitum fed rat weight reported by Daw et al. (1988) for lZmonth-old animals which ate 65-70% of ad libitum intake. Although the animals in the Daw et al. (1988) study were restricted by alternate day feeding rather than daily restriction as in our study, the reduction of food intake was similar between the studies, as was the reduction of body weight. Food restriction also reduces hind limb muscle weight. In food restricted animals, SOL muscle weight was reduced to 84%, PLN weight to 79%, and EDL weight to 89% of the weight of these muscles in ad libitum fed rats. This is not as great as the reductions to 79% and 77% for SOL and EDL, respectively, in the Daw et al. (1988) study. We cannot determine whether the animals in the Daw et al. study were sacrificed on a day after food was given or a day after food was withheld, but if the latter is the case, this may account for the small differences observed between studies. Because food restriction caused greater reduction of body weight than the weight of hind limb muscles, the net result was increased muscle weight to body weight ratio in food restricted rats. The greater relative reduction of body weight than muscle weight likely indicates reduction of body fat, and may include other relatively smaller organs in food restricted animals, but we have no data with which to address this point. Our values of 84%, 1% and 15% for Type I, IIc, and 110 fibers in SOL muscle of sedentary control rats compare favorably with the 81%, 8%, and 11% values reported by Eddinger et al. (1985). For EDL muscles our values of 6%, 49% and 45% for Type I, 110, and IIg fibers are quite different from the 3%) 16%) and 81% values reported for Type I, IIa, and IIb fibers by Eddinger et al. (1985).

ET AL.

The discrepancy is likely due to the classification of fibers based solely on sections incubated for myofibrillar ATPase after acid preincubation in Eddinger’s study, while we based classification on both myofibrillar ATPase and NADH-TR activities. Food restriction had no effect on the percentage of fiber types in any of the hind limb muscles we studied. Endurance training increased the percentage of Type 110 fibers in PLN muscles of ad libitum fed rats. Based on previous studies in rats (Barnard et al., 1971) and guinea pigs (Maxwell et al., 1973), this is the expected response to endurance training in this muscle. There was no alteration of the percentage in fiber types in either SOL or EDL muscles in response to endurance training. Oxidative capacity likely increased in SOL muscle fibers, but this would not be readily detectable as a change in fiber type because SOL is comprised exclusively of oxidative fibers even in control rats. The EDL muscle is not a weight bearing muscle, and is likely not heavily recruited for the performance of treadmill running. The lack of endurance training effect in this muscle indicates the specificity of the response for those muscles involved in the endurance exercise performed. An endurance training effect on SOL muscles of ad libitum fed rats is indicated by increased MFCSA and increased mean fiber area of Type I and Type II muscle fibers. Endurance training had no significant effect on PLN or EDL muscle fiber areas. The results of food restriction or endurance exercise show that each of these experimental manipulations were effective at inducing changes in hind limb skeletal muscles. From this background, the question of whether food restriction impairs the adaptive response of skeletal muscles to endurance training can be examined. Changes in the percentage of Type 110 fibers following endurance training occurred to an equivalent extent in PLN muscles of ad libitum and food restricted rats. No change in the percentage of fiber types occurred in the other muscles in response to food restriction or endurance training. Therefore, we conclude that food restriction did not impair the adaptive increase in oxidative capacity in response to endurance training. Endurance training increased the mean fiber area of all soleus muscle fiber types in ad libitum fed animals.

EFFECTS OF EXERCISE

AND FOOD RESTRICTION

The 26% increase in SOL MFCSA is greater than the 11% increase in SOL muscle weight. In food restricted animals subjected to endurance training, the SOL fiber area was greater than for sedentary animals, but the difference did not reach the level of significance. Although endurance training in ad fibitum fed animals produced only a slight, nonsignificant increase in Type IIg fiber area, and food restriction produced a slight, nonsignificant decrease in Type IIg fiber area, the resultant of these effects is significantly smaller Type IIg fibers in EDL of food restricted than ad libitum fed endurance trained rats. These results are consistent with our conclusion that food restriction impairs adaptive hypertrophy of soleus and extensor

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digitorum longus muscle fibers in response to endurance training. Impaired muscle fiber hypertrophy in food restricted, endurance trained rats may be a functional correlate of the prevention by food restriction of the endurance training induced increases in collagen fibril cross-sectional area which is reported in the accompanying paper (Enwemeka et al., see pp 499-510). Acknowledgements The technical assistance of MS Ann Maxwell and MS Melanie Moody is acknowledged and appreciated. The research was supported in part by NIH grants HL 38427, AG 01188 and a grant from Morrison Trust.

References Barnard. R. J., Edgerton. V. R. and Peter, J. B. 1971. Effect of exercise on skeletal muscle 1. Biochemical and histochemical properties. J. Appl. Physiol., 28(6), 762-766. Beyer. R. E.. Starnes, J. W., Edington, D. W., Lipton, R. J., Compton, R. T. and Kwasman, M. A. 1984. Exerciseinduced reversal of age-related declines of oxidative reactions, mitochondrial yield. and Ravins in skeletal muscles of the rat. Mech. Ageing Dew, 24,309-323. Boreham, C. A., Watt, P. W., Williams, P. E., Merry, B. J. et al. 1988. Effects of ageing and chronic dietary restriction on the morphology of fast and slow muscles of the rat. J. Anat., 157, 111-125. Cerami, A. 1985. Hypothesis: Glucose as a mediator of aging. J. Am. Geriatr. Sot., 33, 626634. Daw, C. K., Starnes, J. W. and White, T. P. 1988. Muscle atrophy and hypoplasia with aging: impact of training and food restriction. J. Applied Physiol., 64(6), 2428-2432. Dubowitz, V. and Brooke, M. H. 1973. Muscle Biopsy: A modern Approach. Saunders, Philadelphia, Dureuil, B.. Viires. N., Veber, B., Pavlovic, D.. et al. 1989. Acute diaphragmatic changes induced by starvation in rats. Am. J. Clin. Nutr., 49(5), 738-744. Eddinger. T. J., Moss, R. L. and Cassens, R. G. 1985. Fiber number and type composition in extensor digitorum longus, soleus, and diaphragm muscles with aging in Fisher 344 rats. J. Histochem. Cytochem., 33(10). 1033-1041. Edelman. N. H.. Rucker, R. B. and Peavey, H. 1986. Nutrition and the respiratory system: Chronic obstructive pulmonary disease (COPD). Am. Reu. Rap. Dis., 134, 347-352. el Haj. A. J., Lewis, S. E.. Goldspink, D. F., Merry, B. J. and Holehan, A. M. 1986. The effect of acute and chronic dietary restriction on the growth and protein turnover of fast and slow types of rat skeletal muscle. Camp. Biochem. Physiol., [A] 85(2), 281-287. Enwemeka, C. S., Maxwell, L. C. and Fernandes, G. Ultrastructural morphometry of matrical changes induced by exercise and food restriction in the rat calcaneal tendon. Tissue Cell (This volume). Goldspink. D. F., el Haj, A. J.. Lewis, S. E., Merry, B. J. and Holehan. A. M. 1987. The influence of chronic dretary intervention on protein turnover and growth of the diaphragm and extensor digitorum longus muscles of the rat. Exp. Gerontol., 22(l), 67-78. Holloszy. J. 0. 1975. Adaptation of skeletal muscles to endurance exercise. Med. Sci. Sports Exert.. 7, 155-164. Holloszy, J. 0. and Coyle, E. F. 1984. Adaptations of skeletal muscle to endurance exercise and their metabolic consequences. J. Appl. Physiol.: Respirat., Enuiron. Exercise Physiology, 56(4), 831-838. Holloszy, J. 0. and Schectman, K. B. 1991. Interaction between exercise and food restriction: effects on longevny of male rats. J. Appl. Physiol., 70(4), 152%1535. Holness. M. J., Lui, Y. L. and Sugden, M. C. Time course of the responses of pyruvate dehydrogenase activitres to short-term starvation in diaphragm and selected skeletal muscles of the rat. Biochem. J., 264(3), 771-776. Kelsen. S. G., Ference, M. and Kapoor, S. 1989. Effects of prolonged undernutrition on structure and function of the diaphragm. J. Appl. Physiol., 58(4), 1354-1359, 1985. Laganiere, S. and Fernades, G. Study of the lipid composition of aging Fischer 344 rat lymphoid cells: Effect of longterm food restriction. Lipids. 26, 472-478, 1991.

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Laganiere, S. and Yu, B. P. 1989. Effect of food restriction in aging rats: II. Liver cytosolic antioxidants and related enzymes. Mech. Aging Dee., 48,221-230. Lewis, M. I. and Sieck, G. C. 1990. Effect of acute nutritional deprivation on diaphragm structure and function. J. Applied Physiol., 68(S), 1938-1944.

Maxwell, L. C., Faulkner, J. A. and Lieberman, D. A. 1973. Histochemical manifestations of age and endurance training in skeletal muscle fibers. Am. J. Physiol., 224, 356-361. Lieberman, D. A., Maxwell, L. C. and Faulkner, J. A. 1972. Adaptation of guinea pig diaphragm muscle to aging and endurance training. Am. .I. Physiol., 222, 556560. Maeda, H., Gleiser, C. A., Masoro, E. J., Murata, I., McMahan, C. A., Yu, B. P. 1985. Nutritional influences on aging of Fischer 344 rats. II Pathology. J. Geronrol., 40,671-688. Masoro, E. J. 1989. Nutrition and aging in animal models. In Nunirion, Aging and the Elderly (eds. H. N. Munro and D. E. Danford). Plenum Pub. Corp., New York. McCarter, R. J. M. 1990. Age-related changes in skeletal muscle function. Aging, 2, 27-38. McCarter, R. and McGee, J. 1987. Influence of nutrition and aging on the composition and function of rat skeletal muscle. J. Geronfol., 42, 432-441. Sieck, G. C., Lewis, M. 1. and Blanco, C. E. 1989. Effects of undernutrition on diaphragm fiber size, SDH activity and fatigue resistance. J. Appl. Physiol., 66(5), 2196-2205. Sugden, M. C. and Holness, M. J. 1989. Effects of refeeding after prolonged starvation on pyruvate dehydrogenase activities in heart, diaphragm and selected skeletal muscles. Biochem. J., 262(2), 669-772. Yu, B. P., Laganiere, S. and Kim, J. W. 1988. Influence of life prolonging food restriction on membrane lipid peroxidation and antioxidant status. In Oxygen radicaLF in Biology and Medicine (eds. G. M. Simic, K. A. Taylor, J. F. van Sonntag Ward), pp. 1067-1073. Plenum Pub. Corp., New York. Yu, B. P., Masoro, E. J. and McMahan, C. A. 1985. Nutritional influences of aging on Fischer 344 rats: I. Physical, metabolic and longevity characteristics. J. Gerontology, 40(6), 657-670. Zar, J. 1974. Biosratisrical Analysis. Prentiss Hall, Inc., Englewood Cliffs, New Jersey.

Effects of exercise and food restriction on rat skeletal muscles.

Studies were undertaken to compare the effects of exercise and food restriction on body weight (BW), muscle weight (MW), muscle fiber size, and propor...
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