Endurance training attenuates the decrease in skeletal muscle malonyl-CoA with exercise

Hutber, C. Adrian, B. B. Rasmussen, and W. W. Winder.Endurance training attenuates the decrease in skeletal muscle malonyl-CoA with exercise. J. Appl.Physiol. 83(6): 1917-1922, 1997.Musclemalonyl-CoA has been postulated to regulate fatty acid metabolism byinhibiting carnitine palmitoyltransferase 1. In nontrained rats,malonyl-CoA decreases in working muscle during exercise. Endurancetraining is known to increase a muscle's reliance on fatty acids as asubstrate. This study was designed to investigate whether the declinein malonyl-CoA with exercise would be greater in trained than innontrained muscle, thereby allowing increased fatty acid oxidation.After 6-10 wk of endurance training (2 h/day) or treadmillhabituation (5-10 min/day), rats were killed at rest or afterrunning up a 15% grade at 21 m/min for 5, 20, or 60 min. Trainingattenuated the exercise-induced drop in malonyl-CoA and prevented theexercise-induced increase in the constant for citrate activation ofacetyl-CoA carboxylase in the red quadriceps muscle of rats run for 20 and 60 min. Hence, contrary to expectations, the decrease inmalonyl-CoA was less in trained than in nontrained muscle during asingle bout of prolonged submaximal exercise.

     

Enlargement of glycogen store in rat liver and muscle by fructose-diet intake and exercise training

Murakami, Taro, Yoshiharu Shimomura, Noriaki Fujitsuka,Masahiro Sokabe, Koji Okamura, and Shuichi Sakamoto. Enlargement of glycogen store in rat liver and muscle by fructose-diet intake andexercise training. J. Appl. Physiol.82(3): 772-775, 1997.This study investigated the effect oflong-term intake of a fructose diet and exercise training on glycogencontent in liver and skeletal muscle in female rats. Thirty-six rats (8 wk old) were divided into two dietary groups and were fed with acontrol (chow) diet or fructose diet (containing 20% fructose) for 12 wk. During this period, one-half of the rats in each dietary group weretrained by using a motor-driven treadmill (running speed of 25 m/minand duration of 90 min/day, 5 days/wk). The liver glycogen wasincreased by intake of a fructose diet and exercise training, and thecontent was in the following order: control-diet and sedentary rats < fructose-diet and sedentary rats  control-diet and trained rats < fructose-diet and trained rats in the ratio of 1:3.4:3.6:5.0. Theglycogen content in gastrocnemius muscle showed the same trend as thatin liver; the ratio was 1:1.3:1.3:1.6. These results indicate that bothlong-term intake of the fructose diet and exercise training synergistically increased glycogen in both tissues.

     

Muscle protein metabolism in female swimmers after a combination of resistance and endurance exercise

Tipton, Kevin D., Arny A. Ferrando, Bradley D. Williams, andRobert R. Wolfe. Muscle protein metabolism in female swimmers after a combination of resistance and endurance exercise.J. Appl. Physiol. 81(5):2034-2038, 1996.There is little known about the responses ofmuscle protein metabolism in women to exercise. Furthermore, the effectof adding resistance training to an endurance training regimen on netprotein anabolism has not been established in either men or women. Thepurpose of this study was to quantify the acute effects of combinedswimming and resistance training on protein metabolism in femaleswimmers by the direct measurement of muscle protein synthesis andwhole body protein degradation. Seven collegiate female swimmers wereeach studied on four separate occasions with a primed constant infusionofring-[¹³C₆]phenylalanine(Phe) to measure the fractional synthetic rate (FSR) of the posteriordeltoid and whole body protein breakdown. Measurements were made over a5-h period at rest and after each of three randomly ordered workouts:1) 4,600 m of intense interval swimming (SW); 2) a whole bodyresistance-training workout with no swimming on that day (RW); and3) swimming and resistance training combined (SR). Whole body protein breakdown was similar for all treatments (0.75 ± 0.04, 0.69 ± 0.03, 0.69 ± 0.02, and 0.71 ± 0.04 µmol ^· min^{1 ·} kg¹for rest, RW, SW, and SR, respectively). The FSR of the posterior deltoid was significantly greater (P < 0.05) after SR (0.082 ± 0.015%/h) than at rest (0.045 ± 0.006%/h). There was no significant difference in the FSR after RW(0.048 ± 0.004%/h) or SW (0.064 ± 0.008%/h) from rest or fromSR. These data indicate that the combination of swimming and resistanceexercise stimulates net muscle protein synthesis above resting levelsin female swimmers.

     

Exercise and exhaustion effects on glycogen synthesis pathways

Gunderson, Hans, Nadja Wehmeyer, Diane Burnett, John Nauman,Cynthia Hartzell, and Scott Savage. Exercise and exhaustion effects on glycogen synthesis pathways. J. Appl.Physiol. 81(5): 2020-2026, 1996.FemaleSprague-Dawley rats were infused with [1-¹³C]glucose tomeasure the effect of endurance training and the effect of variousmetabolic conditions on pathways of hepatic glycogen synthesis. Fourmetabolic states [sedentary (S), trained (T), sedentary exhausted(SE), and trained exhausted (TE)] were studied. T and TE ratswere trained on a motor-driven treadmill (30 m/min, 15% grade, 1.0 h/day, 5 days/wk) for 8-10 wk. After a 24-h fast, SE and TE ratswere run to exhaustion (sedentary average = 78 min, trained average = 155 min) at a training pace and immediately infused with labeledglucose for 2 h. S and T rats were infused after a 24-h fast. Afterinfusion, tissues were removed and glycogen was isolated and hydrolyzedto glucose. The glucose was measured for distribution of¹³C by using nuclear magneticresonance. Glycogen was synthesized predominantly by the indirectpathway for all metabolic states, indicating that infused glucose wasfirst metabolized primarily in the peripheral tissue. Thedirect-pathway utilization was greater in rested S than in rested Tanimals (30 vs. 14%); however, for exhausted animals, the trained useof the direct pathway was greater (22 vs. 9%). Both TE and rested Tanimals utilize the indirect pathway a comparable amount. Sedentaryanimals, on the other hand, dramatically decreased utilization of thedirect pathway, with exhaustive exercise changing from 30 to 9%. Theresults indicate that endurance training modifies glucose utilizationduring glycogen synthesis after fasting and exhaustive exercise.

     

Long-term creatine intake is beneficial to muscle performance during resistance training

Vandenberghe, K., M. Goris, P. Van Hecke, M. Van Leemputte,L. Vangerven, and P. Hespel. Long-term creatine intake isbeneficial to muscle performance during resistance training. J. Appl. Physiol. 83(6):2055-2063, 1997.The effects of oral creatine supplementation onmuscle phosphocreatine (PCr) concentration, muscle strength, and bodycomposition were investigated in young female volunteers(n = 19) during 10 wk ofresistance training (3 h/wk). Compared with placebo, 4 days ofhigh-dose creatine intake (20 g/day) increased(P < 0.05) muscle PCr concentration by 6%. Thereafter, this increase was maintained during 10 wk of training associated with low-dose creatine intake (5 g/day).Compared with placebo, maximal strength of the muscle groups trained,maximal intermittent exercise capacity of the arm flexors, and fat-free mass were increased 20-25, 10-25, and 60% more(P < 0.05), respectively, duringcreatine supplementation. Muscle PCr and strength, intermittent exercise capacity, and fat-free mass subsequently remained at a higherlevel in the creatine group than in the placebo group during 10 wk ofdetraining while low-dose creatine was continued. Finally, on cessationof creatine intake, muscle PCr in the creatine group returned to normalwithin 4 wk. It is concluded that long-term creatine supplementationenhances the progress of muscle strength during resistance training insedentary females.

     

Exercise performance, red blood cell deformability, and lipid peroxidation: effects of fish oil and vitamin E

Oostenbrug, G. S., R. P. Mensink, M. R. Hardeman, T. DeVries, F. Brouns, and G. Hornstra. Exercise performance, red bloodcell deformability, and lipid peroxidation: effects of fish oil andvitamin E. J. Appl. Physiol. 83(3):746-752, 1997.Previous studies have indicated that fish oilsupplementation increases red blood cell (RBC) deformability, which mayimprove exercise performance. Exercise alone, or in combination with anincrease in fatty acid unsaturation, however, may enhance lipidperoxidation. Effects of a bicycle time trial of ~1 h on RBCcharacteristics and lipid peroxidation were, therefore, studied in 24 trained cyclists. After 3 wk of fish oil supplementation (6 g/day),without or with vitamin E (300 IU/day), trial performance,RBC characteristics, and lipid peroxidation were measuredagain. RBC deformability appeared to decrease duringendurance exercise. After correction for hemoconcentration, plasmatotal tocopherol concentrations decreased by 0.77 µmol/l(P = 0.012) or 2.9% and carotenoidconcentrations by 0.08 µmol/l (P = 0.0008) or 4.5%. Endurance exercise did not affect the lag time andrate of in vitro oxidation of low-density lipoproteins (LDLs), but themaximum amount of conjugated dienes formed decreased by 2.1 ± 1.0 µmol/mmol LDL cholesterol (P = 0.042) or 1.2%. Fish oil supplementation with andwithout vitamin E did not affect RBC characteristics or exerciseperformance. Both supplements decreased the rate of LDL oxidation, andfish oil supplementation with vitamin E delayed oxidation. The amountof dienes, however, was not affected. The supplements also did notchange effects of exercise. We conclude that the changes observedduring endurance exercise may indicate increased oxidative stress, butfurther research is necessary to confirm this. Fish oil supplementation does not improve endurance performance, but it also does not cause oraugment changes in antioxidant levels or LDL oxidation during exercise.

     

Changes in insulin-stimulated glucose transport and GLUT-4 protein in rat skeletal muscle after training

Kawanaka, Kentaro, Izumi Tabata, Shigeru Katsuta, andMitsuru Higuchi. Changes in insulin-stimulated glucose transport and GLUT-4 protein in rat skeletal muscle after training.J. Appl. Physiol. 83(6):2043-2047, 1997.After running training, which increased GLUT-4protein content in rat skeletal muscle by <40% compared with controlrats, the training effect on insulin-stimulated maximal glucosetransport (insulin responsiveness) in skeletal muscle was short lived(24 h). A recent study reported that GLUT-4 protein content in ratepitrochlearis muscle increased dramatically (~2-fold) after swimmingtraining (J.-M. Ren, C. F. Semenkovich, E. A. Gulve, J. Gao, andJ. O. Holloszy. J. Biol.Chem. 269, 14396-14401, 1994).Because GLUT-4 protein content is known to be closely related toskeletal muscle insulin responsiveness, we thought it possible that thetraining effect on insulin responsiveness may remain for >24 h afterswimming training if GLUT-4 protein content decreases gradually fromthe relatively high level and still remains higher than control levelfor >24 h after swimming training. Therefore, we examined thispossibility. Male Sprague-Dawley rats swam 2 h a day for 5 days with aweight equal to 2% of body mass. Approximately 18, 42, and 90 h aftercessation of training, GLUT-4 protein concentration and2-[1,2-³H]deoxy-D-glucosetransport in the presence of a maximally stimulating concentration ofinsulin (2 mU/ml) were examined by using incubated epitrochlearismuscle preparation. Swimming training increased GLUT-4 proteinconcentration and insulin responsiveness by 87 and 85%, respectively,relative to age-matched controls when examined 18 h after training.Forty-two hours after training, GLUT-4 protein concentration andinsulin responsiveness were still higher by 52 and 51%, respectively,in muscle from trained rats compared with control. GLUT-4 proteinconcentration and insulin responsiveness in trained muscle returned tosedentary control level within 90 h after training. We conclude that1) the change in insulinresponsiveness during detraining is directly related to muscle GLUT-4protein content, and 2)consequently, the greater the increase in GLUT-4 protein content thatis induced by training, the longer an effect on insulin responsivenesspersists after the training.

     

Voluntary running induces fiber type-specific angiogenesis in mouse skeletal muscle

Adult skeletal muscle undergoes adaptation in response to endurance exercise, including fast-to-slow fiber type transformation and enhanced angiogenesis. The purpose of this study was to determine the temporal and spatial changes in fiber type composition and capillary density in a mouse model of endurance training. Long-term voluntary running (4 wk) in C57BL/6 mice resulted in an approximately twofold increase in capillary density and capillary-to-fiber ratio in plantaris muscle as measured by indirect immunofluorescence with an antibody against the endothelial cell marker CD31 (466 ± 16 capillaries/mm² and 0.95 ± 0.04 capillaries/fiber in sedentary control mice vs. 909 ± 55 capillaries/mm² and 1.70 ± 0.04 capillaries/fiber in trained mice, respectively; P < 0.001). A significant increase in capillary-to-fiber ratio was present at day 7 with increased concentration of vascular endothelial growth factor (VEGF) in the muscle, before a significant increase in percentage of type IIa myofibers, suggesting that exercise-induced angiogenesis occurs first, followed by fiber type transformation. Further analysis with simultaneous staining of endothelial cells and isoforms of myosin heavy chains (MHCs) showed that the increase in capillary contact manifested transiently in type IIb + IId/x fibers at the time (day 7) of significant increase in total capillary density. These findings suggest that endurance training induces angiogenesis in a subpopulation of type IIb + IId/x fibers before switching to type IIa fibers. adaptation; capillary density; endothelial cells; fiber type transformation; vascular endothelial growth factor     

Endurance training affects myosin heavy chain phenotype in regenerating fast-twitch muscle

Bigard, Xavier A., Chantal Janmot, Danièle Merino,Françoise Lienhard, Yannick C. Guezennec, and Anne D'Albis.Endurance training affects myosin heavy chain phenotype inregenerating fast-twitch muscle. J. Appl.Physiol. 81(6): 2658-2665, 1996.The aim of thisstudy was to analyze the effects of treadmill training (2 h/day, 5 days/wk, 30 m/min, 7% grade for 5 wk) on the expression of myosinheavy chain (MHC) isoforms during and after regeneration of afast-twitch white muscle [extensor digitorum longus (EDL)]. Male Wistar rats were randomly assigned to a sedentary(n = 10) or an endurance-trained (ET;n = 10) group. EDL muscle degeneration and regeneration were induced by two subcutaneous injections of a snaketoxin. Five days after induction of muscle injury, animals were trainedover a 5-wk period. It was verified that ~40 days after venomtreatment, central nuclei were present in the treated EDL muscles fromsedentary and ET rats. The changes in the expression of MHCs in EDLmuscles were detected by using a combination of biochemical andimmunocytochemical approaches. Compared with contralateral nondegenerated muscles, relative concentrations of types I, IIa, andIIx MHC isoforms in ET rats were greater in regenerated EDL muscles(146%, P < 0.05; 76%,P < 0.01; 87%,P < 0.01, respectively). Their elevation corresponded to a decreasein the relative concentration of type IIb MHC (36%,P < 0.01). Although type I accountedfor only 3.2% of total myosin in regenerated muscles from the ETgroup, the cytochemical analysis showed that the proportion of positive staining with the slow MHC antibody was markedly greater in regenerated muscles than in contralateral ones. Collectively, these results demonstrate that the regenerated EDL muscle is sensitive to endurance training and suggest that the training-induced shift in MHC isoforms observed in these muscles resulted from an additive effect of regeneration and repeated exercise.

     

More tetanic contractions are required for activating glucose transport maximally in trained muscle

Kawanaka, Kentaro, Izumi Tabata, and MitsuruHiguchi. More tetanic contractions are requiredfor activating glucose transport maximally in trained muscle.J. Appl. Physiol. 83(2): 429-433, 1997.Exercise training increases contraction-stimulated maximalglucose transport and muscle glycogen level in skeletal muscle.However, there is a possibility that more muscle contractions arerequired to maximally activate glucose transport in trained than inuntrained muscle, because increased glycogen level after training mayinhibit glucose transport. Therefore, the purpose of this study was toinvestigate the relationship between the increase in glucose transportand the number of tetanic contractions in trained and untrained muscle.Male rats swam 2 h/day for 15 days. In untrained epitrochlearis muscle,resting glycogen was 26.6 µmol glucose/g muscle. Ten, 10-s-longtetani at a rate of 1 contraction/min decreased glycogen level to 15.4 µmol glucose/g muscle and maximally increased2-deoxy-D-glucose(2-DG) transport. Training increasedcontraction-stimulated maximal 2-DG transport (+71%;P < 0.01), GLUT-4 protein content(+78%; P < 0.01), and restingglycogen level (to 39.3 µmol glucose/g muscle;P < 0.01) on the next day after thetraining ended, although this training effect might be due, at least inpart, to last bout of exercise. In trained muscle, 20 tetani werenecessary to maximally activate glucose transport. Twenty tetanidecreased muscle glycogen to a lower level than 10 tetani (18.9 vs.24.0 µmol glucose/g muscle; P < 0.01). Contraction-stimulated 2-DG transport was negatively correlatedwith postcontraction muscle glycogen level in trained (r = 0.60;P < 0.01) and untrained muscle(r = 0.57;P < 0.01).

     

Effect of exercise training on passive stiffness in locomotor skeletal muscle: role of extracellular matrix

The purpose ofthis study was to evaluate the effect of endurance exercise training onboth locomotor skeletal muscle collagen characteristics and passivestiffness properties in the young adult and old rat. Young(3-mo-old) and senescent (23-mo-old) male Fischer 344 rats wererandomly assigned to either a control or exercise training group[young control (YC), old control (OC), young trained (YT), oldtrained (OT)]. Exercise training consisted of treadmill runningat ~70% of maximal oxygen consumption (45 min/day, 5 days/wk, for 10 wk). Passive stiffness (stress/strain) of the soleus (Sol) muscle fromall four groups was subsequently measured in vitro at 26°C.Stiffness was significantly greater for Sol muscles in OC rats comparedwith YC rats, but in OT rats exercise training resulted in muscles withstiffness characteristics not different from those in YC rats. Solmuscle collagen concentration and the level of the nonreduciblecollagen cross-link hydroxylysylpyridinoline (HP) significantlyincreased from young adulthood to senescence. Although training had noeffect on Sol muscle collagen concentration in either age group, itresulted in a significant reduction in the level of Sol muscle HP in OTrats. In contrast, exercise had no effect on HP in the YT animals.These findings indicate that 10 wk of endurance exercise significantlyalter the passive viscoelastic properties of Sol muscle in old but notin young adult rats. The coincidental reduction in the principalcollagen cross-link HP also observed in response to training in OTmuscle highlights the potential role of collagen in influencing passivemuscle viscoelastic properties.

     

Skeletal muscle biochemical adaptations to exercise training in miniature swine

McAllister, Richard M., Brian L. Reiter, John F. Amann, andM. Harold Laughlin. Skeletal muscle biochemical adaptations toexercise training in miniature swine. J. Appl.Physiol. 82(6): 1862-1868, 1997.The primarypurpose of this study was to test the hypothesis that enduranceexercise training induces increased oxidative capacity in porcineskeletal muscle. To test this hypothesis, female miniature swine wereeither trained by treadmill running 5 days/wk over 16-20 wk (Trn;n = 35) or pen confined (Sed;n = 33). Myocardialhypertrophy, lower heart rates during submaximal stages of a maximaltreadmill running test, and increased running time to exhaustion duringthat test were indicative of training efficacy. A variety of skeletalmuscles were sampled and subsequently assayed for the enzymes citratesynthase (CS), 3-hydroxyacyl-CoA dehydrogenase, and lactatedehydrogenase and for antioxidant enzymes. Fiber type composition of arepresentative muscle was also determined histochemically. The largestincrease in CS activity (62%) was found in the gluteus maximus muscle(Sed, 14.7 ± 1.1 µmol · min¹ · g¹;Trn, 23.9 ± 1.0; P < 0.0005).Muscles exhibiting increased CS activity, however, were locatedprimarily in the forelimb; ankle and knee extensor and respiratorymuscles were unchanged with training. Only two muscles exhibited higher3-hydroxyacyl-CoA dehydrogenase activity in Trn compared with Sed.Lactate dehydrogenase activity was unchanged with training, as wereactivities of antioxidant enzymes. Histochemical analysis of thetriceps brachii muscle (long head) revealed lower type IIB fibernumbers in Trn (Sed, 42 ± 6%; Trn, 10 ± 4;P < 0.01) and greater type IID/Xfiber numbers (Sed, 11 ± 2; Trn, 22 ± 3;P < 0.025). These findingsindicate that porcine skeletal muscle adapts to endurance exercisetraining in a manner similar to muscle of humans and other animalmodels, with increased oxidative capacity. Specificmuscles exhibiting these adaptations, however, differ between theminiature swine and other species.

     

Persistence of supercompensated muscle glycogen in trained subjects after carbohydrate loading

Goforth, Jr., Harold W., David A. Arnall, Brad L. Bennett,and Patricia G. Law. Persistence of supercompensated muscle glycogen in trained subjects after carbohydrate loading.J. Appl. Physiol. 82(1): 342-347, 1997.Several carbohydrate (CHO)-loading protocols have been used toachieve muscle glycogen supercompensation and prolong enduranceperformance. This study assessed the persistence of muscle glycogensupercompensation over the 3 days after the supercompensation protocol.Trained male athletes completed a 6-day CHO-loading protocol thatincluded cycle ergometer exercise and dietary manipulations. The 3-daydepletion phase began with 115 min of cycling at 75% peak oxygenuptake followed by 3 × 60-s sprints and included the subjectsconsuming a low-CHO/high-protein/high-fat (10:41:49%) diet. Subjectscycled 40 min at the same intensity for the next 2 days. During the3-day repletion phase, subjects rested and consumed ahigh-CHO/low-protein/low-fat (85:08:07%) diet, including aglucose-polymer beverage. A 3-day postloading phase followed, whichinvolved a moderately high CHO diet (60%) and no exercise. Glycogenvalues for vastus lateralis biopsies at baseline and postloadingdays 1-3 were 408 ± 168 (SD),729 ± 222, 648 ± 186, and 714 ± 196 mmol/kg dry wt,respectively. The CHO-loading protocol increased muscle glycogen by1.79 times baseline, and muscle glycogen remained near this levelduring the 3-day postloading period. Results indicate thatsupercompensated muscle glycogen levels can be maintained for at least3 days in a resting athlete when a moderate-CHO diet is consumed.

     

Concurrent resistance and endurance training influence basal metabolic rate in nondieting individuals

Thirty physically active healthy men (20.1 ± 1.6 yr) wererandomly assigned to participate for 10 wk in one of the following training groups: endurance trained (ET; 3 days/wk joggingand/or running), resistance trained (RT; 3 days/wkresistance training), or combined endurance and resistance trained(CT). Before and after training, basal metabolic rate (BMR), percentbody fat (BF), maximal aerobic power, and one-repetition maximum forbench press and parallel squat were determined for each subject.Urinary urea nitrogen was determined pre-, mid-, and posttraining. BMRincreased significantly from pre- to posttraining for RT (7,613 ± 968 to 8,090 ± 951 kJ/day) and CT (7,455 ± 964 to 7,802 ± 981 kJ/day) but not for ET (7,231 ± 554 to 7,029 ± 666 kJ/day).BF for CT (12.2 ± 3.5 to 8.7 ± 1.7%) was significantly reducedcompared with RT (15.4 ± 2.7 to 14.0 ± 2.7%) and ET (11.8 ± 2.9 to 9.5 ± 1.7%). Maximal aerobic power increasedsignificantly for ET (13%) but not RT (0.2%) or CT (7%),whereas the improvements in one-repetition maximum bench press andparallel squat were greater in RT (24 and 23%, respectively) comparedwith CT (19 and 12%, respectively). Urinary urea nitrogen loss wasgreater in ET (14.6 ± 0.9 g/24 h) than in RT (11.7 ± 1.0 g/24h) and CT (11.5 ± 1.0 g/24 h) at the end of 10 wk oftraining. These data indicate that, although RT alone will increase BMRand muscular strength, and ET alone will increase aerobic power anddecrease BF, CT will provide all of these benefits but to a lessermagnitude than RT and ET after 10 wk of training.

     

Endurance in high-fat-fed rats: effects of carbohydrate content and fatty acid profile

The purpose ofthis experiment was to study endurance performance and substratestorage and utilization in fat- or carbohydrate-fed rats. Ninety-ninerats were randomly divided into three groups and over 4 wk were fedeither a carbohydrate-rich [CHO; 10% total energy content in the diet(E%) fat, 20 E% protein, 70 E% carbohydrate] diet or one of twofat-rich diets (65 E% fat, 20 E% protein, 15 E% carbohydrate)containing either saturated (Sat) or monounsaturated fatty acids(Mono). Each dietary group was randomly assigned to a trained (6 days/wk, progressive to 60 min, 28 m/min at a 10% incline) or asedentary group. Rats were killed either before or after a treadmillendurance run to exhaustion. Training increased endurance (206%), butdiet composition did not affect endurance in either trained orsedentary rats. -Hydroxyacyl-CoA dehydrogenase activity wasincreased in fat-fed but not carbohydrate-fed rats (P < 0.05). Respiratory exchangeratio during the initial phase of exercise was lower after the Monocompared with the Sat diet (P < 0.05) and higher after the CHO than the Sat diet(P < 0.05). Thus adaptation to ahigh-fat diet containing a moderate amount of carbohydrates did notinduce enhanced endurance in either trained or untrained rats; however,substrate utilization was modulated by both amount and type of dietaryfat during the initial stage of exercise in trained and sedentary rats.

     

Endurance exercise modulates neuromuscular junction of C57BL/6NNia aging mice

Fahim, Mohamed A. Endurance exercise modulatesneuromuscular junction of C57BL/6NNia aging mice. J. Appl. Physiol. 83(1): 59-66, 1997.The effect ofage and endurance exercise on the physiology and morphology ofneuromuscular junctions (NMJ) of gluteus maximus muscle was studied inC57BL/6NNia mice. Mice were exercised, starting at 7 or 25 mo of age,at 28 m/min for 60 min/day, 5 days/wk for 12 wk, on a rodent treadmill.Intracellular recordings of spontaneous miniature endplate potentials(MEPP) and the quantal content of endplate potentials (EPP) wererecorded from NMJ of 10- and 28-mo-old control and exercised mice.Endurance exercise resulted in significant increases in MEPP amplitudes (23%), quantal content, and safety margin, and a significant decrease in MEPP frequency of young mice, with no change in resting membrane potential or membrane capacitance. Three months of endurance exercise resulted in an increase in MEPP frequency (41%) and decreases in MEPPamplitudes (15%), quantal content, and safety margin of old mice.Endurance exercise resulted in significantly larger nerve terminals(24%) in young animals, suggesting functional adaptation. Nerveterminals in exercised 28-mo-old mice were smaller than in thecorresponding control mice, an indication that exercise minimizedage-related nerve terminal elaboration. It is concluded that thedifferent physiological responses of young and old gluteus maximusmuscles to endurance exercise parallel their morphological responses.This suggests that the mouse NMJ undergoes a process of physiologicaland morphological remodeling during aging, and such plasticity could bemodulated differently by endurance exercise.

     

Effect of vitamin E deprivation and exercise training on induction of HSP70

Kelly, D. A., P. M. Tiidus, M. E. Houston, and E. G. Noble.Effect of vitamin E deprivation and exercise training on inductionof HSP70. J. Appl. Physiol. 81(6):2379-2385, 1996.To investigate the effects of dietary vitamin Edeprivation and chronic exercise on the relative content of selectedisoforms of the heat-shock protein 70 (HSP70) family in rat hindlimbmuscle, vitamin E was withheld for 16 wk from female rats thatunderwent treadmill run training during the final 8 wk. As indicated byincreased (P < 0.05) content of thestress-inducible isoform (HSP72), training did stress the exercisingmuscles. However, vitamin E deficiency did not alter HSP72 content innontrained rats and was associated with a lesser induction(P < 0.01) in some muscles oftrained animals. The constitutive isoform, which exhibited similarlevels in muscles of varying fiber types, was demonstrated to belargely refractory to exercise, with an equivocal response to vitamin Edeprivation. HSP72 content was correlated to type I myosin heavy chain(MHC-I) content but only in muscles of sedentary normal-diet rats.After training, HSP72 content in a muscle essentially devoid of MHC-I(superficial vastus lateralis) reached levels comparable to those in amuscle high in MHC-I (soleus).

     

Exercise training increases sarcolemmal GLUT-4 protein and mRNA content in diabetic heart

Osborn, Brett A., June T. Daar, Richard A. Laddaga, Fred D. Romano, and Dennis J. Paulson. Exercise training increases sarcolemmal GLUT-4 protein and mRNA content in diabetic heart. J. Appl. Physiol. 82(3): 828-834, 1997.This study determined whether dynamic exercise training ofdiabetic rats would increase the expression of the GLUT-4 glucosetransport protein in prepared cardiac sarcolemmal membranes. Fourgroups were compared: sedentary control, sedentary diabetic, trainedcontrol, and trained diabetic. Diabetes was induced by intravenousstreptozotocin (60 mg/kg). Trained control and diabetic rats were runon a treadmill for 60 min, 27 m/min, 10% grade, 6 days/wk for 10 wk.Sarcolemmal membranes were isolated by using differentialcentrifugation, and the activity of sarcolemmalK⁺-p-nitrophenylphosphatase( pNPPase; an indicator ofNa⁺-K⁺-adenosinetriphosphataseactivity) was quantified. Hearts from the sedentary diabetic groupexhibited a significant depression of sarcolemmal pNPPaseactivity. Exercise training did not significantly alterpNPPase activity. Sedentary diabetic rats exhibited an 84 and 58% decrease in GLUT-4 protein and mRNA, respectively, relative tocontrol rats. In the trained diabetic animals, sarcolemmal GLUT-4protein levels were only reduced by 50% relative to control values,whereas GLUT-4 mRNA were returned to control levels. The increase inmyocardial sarcolemmal GLUT-4 may be beneficial to the diabetic heartby enhancing myocardial glucose oxidation and cardiac performance

     

Rapid reversal of adaptive increases in muscle GLUT-4 and glucose transport capacity after training cessation

Previous studies have shown that when exercise isstopped there is a rapid reversal of the training-induced adaptiveincrease in muscle glucose transport capacity. Endurance exercisetraining brings about an increase in GLUT-4 in skeletal muscle. Theprimary purpose of this study was to determine whether the rapidreversal of the increase in maximally insulin-stimulated glucosetransport after cessation of training can be explained by a similarlyrapid decrease in GLUT-4. A second purpose was to evaluate thepossibility, suggested by previous studies, that the magnitude of theadaptive increase in muscle GLUT-4 decreases when exercise training is extended beyond a few days. We found that both GLUT-4 and maximally insulin-stimulated glucose transport were increased approximately twofold in epitrochlearis muscles of rats trained by swimming for 6 h/day for 5 days or 5 wk. GLUT-4 was 90% higher, citrate synthaseactivity was 23% higher, and hexokinase activity was 28% higher intriceps muscle of the 5-day trained animals compared with the controls.The increases in GLUT-4 protein and in insulin-stimulated glucosetransport were completely reversed within 40 h after the last exercisebout, after both 5 days and 5 wk of training. In contrast, theincreases in citrate synthase and hexokinase activities were unchanged40 h after 5 days of exercise. These results support the conclusionthat the rapid reversal of the increase in the insulin responsivenessof muscle glucose transport after cessation of training is explained bythe short half-life of the GLUT-4 protein.

     

Effects of training and a single session of exercise on lipids and apolipoproteins in hypercholesterolemic men

Crouse, Stephen F., Barbara C. O'Brien, Peter W. Grandjean,Robert C. Lowe, J. James Rohack, and John S. Green. Effects oftraining and a single session of exercise on lipids and apolipoproteins in hypercholesterolemic men. J. Appl.Physiol. 83(6): 2019-2028, 1997.To differentiatebetween transient (acute) and training (chronic) effects of exercise attwo different intensities on blood lipids and apolipoproteins (apo), 26 hypercholesterolemic men (cholesterol = 258 mg/dl, age = 47 yr, weight = 81.9 kg) trained three times per week for 24 wk, 350 kcal/session athigh (80% maximal O₂ uptake,n = 12) or moderate (50% maximalO₂ uptake, n = 14) intensity. Serum lipid andapolipoprotein (apo) concentrations (plasma volume adjusted) weremeasured before and immediately, 24, and 48 h after exercise on fourdifferent occasions corresponding to 0, 8, 16, and 24 wk of training.Data were analyzed using three-way repeated-measures multivariateanalysis of variance followed by analysis of variance and Duncan'sprocedures ( = 0.05). A transient 6% rise inlow-density-lipoprotein cholesterol measured before training at the24-h time point was no longer evident after training. Triglyceridesfell and total cholesterol, high-density-lipoprotein cholesterol(HDL-C), HDL₃-C, apo A-I, and apoB rose 24-48 h after exercise regardless of training or intensity.Total cholesterol, HDL₃-C, apoA-I, and apo B were lower andHDL₂-C was higher after trainingthan before training. Thus exercise training and a single session ofexercise exert distinct and interactive effects on lipids andapolipoproteins. These results support the practice of training atleast every other day to obtain optimal exercise benefits.