Final Exercise Bout Research Articles

A Single Bout of Aerobic Exercise Compromises Down-regulation of MuRF Expression Subsequent to Resistance Exercise

While many athletes incorporate both aerobic and resistance exercise in their training regimen, the compatibility of these two exercise modes, each offering a very specific stimulus, has been challenged. Thus, it has been inferred that skeletal muscle adaptations, typical of resistance training, may be hampered if preceded by aerobic exercise. PURPOSE: To explore the effects of acute concurrent aerobic and resistance exercise on molecular markers fundamental to resistance exercise-specific muscle adaptations. METHODS: Nine physically active men (23±2 yrs, 181±6 cm, 75±6 kg) were subjected to an unilateral exercise model over three non-consecutive exercise days within a week, such that one limb was assigned to concurrent knee extensor exercise (AE+RE) and the other limb performed resistance exercise (RE) only. In the morning of each day of exercise, subjects performed ∼45 min unilateral endurance exercise (heart rate and plasma lactate concentration, respectively averaged 162 bpm and 5.7 mmol/l at completion) on a modified cycle ergometer. Six hrs later, unilateral resistance exercise (4 sets of 7 reps of leg press and knee extension) of either limb was performed employing flywheel ergometers. Muscle power of each rep and set was measured. Percutaneous muscle biopsies were obtained from m.vastus lateralis immediately before (PRE), 15 min (POST1) and 3 hrs (POST2) after the final resistance exercise bout. Levels of mRNA of VEGF and PGC-1α were used as endurance markers, and MuRF as a marker for protein regulation. VEGF, PGC-1α and MuRF were measured using RT-PCR and analyzed using ANOVA for repeated measures with a 5% α-level. RESULTS: Peak power (averaged across all days of exercise) was similar (p>0.05) for AE+RE and RE in both the leg press (mean±SE; 233±16 vs. 247±17 W) and the knee extension (342±20 vs. 357±20 W) exercise. Glycogen content was lower in AE+RE than RE (p<0.05). VEGF and PGC-1α mRNA-levels were two- and four-fold higher in AE+RE compared with RE both before (PRE) and after (POST1, POST2) resistance exercise (p<0.05). MuRF expression decreased (25%; p<0.05) after RE, but not after AE+RE (p>0.05). CONCLUSIONS: When performing resistance exercise subsequent to aerobic exercise on the same day, it appears important steps regulating protein turnover in response to resistance exercise are compromised.

Cumulative responses of muscle protein synthesis are augmented with chronic resistance exercise training

The purpose of this study was to determine the anabolic response of a single bout of high intensity resistance exercise (RE) following 5 weeks of RE training. To complete these studies, Sprague-Dawley rats were assigned by body mass to RE, exercise control (EC), or sedentary cage control (CC) groups and studied over 36 h after 5 weeks of RE (squat-like) training. Cumulative (final 36 h) fractional rates of muscle protein synthesis (FSR) were determined by ²H₂O, and acute (16 h post-RE) rates of muscle protein synthesis (RPS) were determined by flooding with l-[2,3,4,5,6-³H]phenylalanine. Regulators of peptide-chain initiation, 4E-BP1, eIF4E and the association of the two were determined by Western blotting and immunoprecipitation respectively. No differences were observed with acute measures of RPS obtained 16 h following the final exercise bout in the plantaris or soleus muscles (P > 0.05). Consistent with this observation, 4E-BP1 was similarly phosphorylated and bound to eIF4E among all groups. However, upon determination of the cumulative response, FSR was significantly increased in the plantaris of RE vs. EC and CC (0.929±0.094, 0.384±0.039, 0.300±0.022% h(-1) respectively; P<0.001), but not the soleus. With the advantage of determining cumulative FSR, the present study demonstrates that anabolic responses to RE are still evident after chronic RE training, primarily in muscle composed of fast-twitch fibres.

Early-Phase Neuroendocrine Responses and Strength Adaptations Following Eccentric-Enhanced Resistance Training

The purpose of this study was to evaluate the early-phase muscular performance adaptations to 5 weeks of traditional (TRAD) and eccentric-enhanced (ECC+) progressive resistance training and to compare the acute postexercise total testosterone (TT), bioavailable testosterone (BT), growth hormone (GH), and lactate responses in TRAD- and ECC+-trained individuals. Twenty-two previously untrained men (22.1 +/- 0.8 years) completed 1 familiarization and 2 baseline bouts, 15 exercise bouts (i.e., 3 times per week for 5 weeks), and 2 postintervention testing bouts. Anthropometric and 1 repetition maximum (1RM) measurements (i.e., bench press and squat) were assessed during both baseline and postintervention testing. Following baseline testing, participants were randomized into TRAD (4 sets of 6 repetitions at 52.5% 1RM) or ECC+ (3 sets of 6 repetitions at 40% 1RM concentric and 100% 1RM eccentric) groups and completed the 5-week progressive resistance training protocols. During the final exercise bout, blood samples acquired at rest and following exercise were assessed for serum TT, BT, GH, and blood lactate. Both groups experienced similar increases in bench press (approximately 10%) and squat (approximately 22%) strength during the exercise intervention. At the conclusion of training, postexercise TT and BT concentrations increased (approximately 13% and 21%, respectively, p < 0.05) and GH concentrations increased (approximately 750-1200%, p < 0.05) acutely following exercise in both protocols. Postexercise lactate accumulation was similar between the TRAD (5.4 +/- 0.4) and ECC+ (5.6 +/- 0.4) groups; however, the ECC+ group's lactate concentrations were significantly lower than those of the TRAD group 30 to 60 minutes into recovery. In conclusion, TRAD training and ECC+ training appear to result in similar muscular strength adaptations and neuroendocrine responses, while postexercise lactate clearance is enhanced following ECC+ training.

Elevation Of Body Temperature Is Associated With Exercise-Increased Extracellular Heat Shock Protein 72 Level In Rat Plasma

PURPOSE: To examine whether exercise-increased extracellular heat shock protein 72 (eHsp72) level is associated with an elevation of body temperature during exercise in rat. METHODS: Twenty-six female Sprague-Dawley rats (3 months old) were assigned to control (CON, n = 8), exercise under warm temperature (WEx, n = 9), and exercise under cold temperature (CEx, n = 9) groups. The WEx and CEx animals were trained respectively using a treadmill for nine days in a climate-controlled room at 25°C or 4°C. The intensity and duration of the training started at 20-25 m·min−1 for 10 min; they were increased to 30 m·min−1 for 60 min until the sixth day. Subsequently, the intensity and duration were maintained until the ninth day. Before and immediately after the final exercise bout, the colonic temperature of each animal was measured as an index of body temperature. The animals were subsequently anesthetized and blood samples were collected. The blood samples were centrifuged and plasma samples were obtained to assess their eHsp72 levels. RESULTS: The body temperature in only WEx animals was significantly (P < 0.05) increased by exercise (basal vs post-exercise body temperature, WEx: 38.3 ± 0.3 vs 40.5 ± 0.3, CEx: 38.2 ± 0.3 vs 38.5 ± 0.6°C). The eHsp72 level in WEx animal was significantly (P < 0.05) higher than those of CON and CEx animals (CON: 1.4 ± 0.3, WEx: 2.6 ± 0.9, CEx: 1.5 ± 0.2 ng·ml−1). Regression analysis revealed that the eHsp72 level increased as a function of the body temperature. CONCLUSIONS: Exercise-increased eHsp72 level is associated with an elevation of body temperature during exercise.

The Influence of Eccentric and Concentric Exercise on Skeletal Muscle Regulators in Young Women

PURPOSE: To evaluate changes in myostatin, follistatin and MyoD mRNA gene expression using concentric exercise (CE) and eccentric exercise (EE) as a stimulus to better understand the mechanisms of muscle hypertrophy in young women. METHODS: Single-leg maximal eccentric or concentric isokinetic exercise was performed using the Cybex NormTM dynamometer (Cybex International Inc. Ronkonkoma, New York) at 60° /s. Ten sets of ten repetitions with 20 second rest between sets were completed by each subject. Three muscle biopsies of the vastus lateralis were obtained from the exercised leg at baseline (1st biopsy), 8 hours after the first exercise bout (2nd biopsy), and 8 hours after the seventh and final exercise bout performed 2 weeks after the first exercise session (3rd biopsy). mRNA gene expression was analyzed using RT-PCR methods. 18s ribosomal RNA was used as the internal standard to determine relative expression of mRNAs for myostatin, follistatin, and MyoD. Paired t-tests were used to compare changes in mRNA gene expression within groups (Eccentric or Concentric). Independent t-tests were performed to test group differences (Eccentric versus Concentric). A probability level of P ≤ 0.05 was used to determine statistical significance with Bonferroni adjustments. RESULTS: There were no significant fold changes in the CE group for myostatin, follistatin, and MyoD mRNA gene expression between the first and second biopsies as well as the first and third biopsies (P>0.17). Similarly, there were no significant changes in the EE group for the same variables (P>0.11). In addition, there were no significant differences between the EE and CE groups (P≥0.05). CONCLUSIONS: Our data suggests that a single bout or multiple bouts (7) of maximal eccentric or concentric exercise does not significantly alter myostatin, follistatin, or MyoD mRNA gene expression in young women. Therefore, the type of exercise stimulus does not appear to differentially alter mRNA gene expression of hypertrophic myogenic regulators.

Elevation of body temperature is an essential factor for exercise-increased extracellular heat shock protein 72 level in rat plasma

This study examined whether the exercise-increased extracellular heat shock protein 72 (eHsp72) levels in rats was associated with body temperature elevation during exercise. In all, 26 female Sprague-Dawley rats (3 mo old) were assigned randomly to control (CON; n = 8), exercise under warm temperature (WEx; n = 9), or exercise under cold temperature (CEx; n = 9). The WEx and CEx were trained at 25 degrees C or 4 degrees C, respectively, for nine days using a treadmill. Before and immediately after the final exercise bout, the colonic temperatures were measured as an index of body temperature. The animals were subsequently anesthetized, and blood samples were collected and centrifuged. Plasma samples were obtained to assess their eHsp72 levels. Only the colonic temperature in WEx was increased significantly (P < 0.05) by exercise. The eHsp72 level in WEx was significantly higher (P < 0.05) than that of either the CON or CEx. However, no significant difference was found between CON and CEx. Regression analyses revealed that the eHsp72 level increased as a function of the body temperature. In another experiment, the eHsp72 level of animals with body temperature that was passively elevated through similar kinetics to those of the exercise was studied. Results of this experiment showed that mere body temperature elevation was insufficient to induce eHsp72 responses. Collectively, our results suggest that body temperature elevation during exercise is important for induction of exercise-increased eHsp72. In addition, the possible role of body temperature elevation is displayed when the exercise stressor is combined with it.

Endurance Training and Obesity

Obesity and type 2 diabetes mellitus are disease states associated with hallmark features such as insulin resistance and an impaired ability to oxidize lipids. It has recently been reported that an optimal exercise intensity for fat oxidation (FATmax) exists; we hypothesize that continuous exercise training at this specific intensity can lead to greater improvements in fat oxidation and insulin sensitivity than a eucaloric interval training program. In a counterbalanced, crossover design, eight sedentary, obese, but otherwise healthy male participants performed two 4-wk blocks of endurance training, either at a predetermined intensity eliciting maximal fat oxidation (TPCON) or at 5-min intervals of +/- 20% FATmax (TPINT). During the week preceding the exercise training and 48 h after the final exercise bout, an OGTT, V O2max test, steady-state exercise, and measurements of body composition were undertaken. Diet was controlled the day before all trials (50% carbohydrate, 35% fat, and 15% protein; approximately 2900 kcal.d). Variables were compared using two-way repeated-measures analyses of variance. It was shown that fat oxidation rates were increased by 44% after TPCON (0.24 +/- 0.01 vs 0.35 +/- 0.03 g.min, P < 0.05) but not after TPINT, and the whole-body insulin sensitivity index was increased by 27% after TPCON (P < 0.05). These changes occurred despite no change in body weight, body mass index (BMI), waist to hip ratio (WHR), percent body fat (%BF), or V O2max. A continuous exercise training protocol that can elicit high rates of fat oxidation increases the contribution of fat to substrate oxidation during exercise and can significantly increase insulin sensitivity compared with a eucaloric interval protocol.

The Effects of Endurance Exercise TVaining on Cardiac Function in VLCAD -/- and LCAD -/- Mice.

Fatty acid oxidation is a crucial pathway for energy production in the heart during strenuous activity. Work in our lab has shown that exercise causes a decline in skeletal muscle function in very-long-chain acyl CoA deficient mice. The affect on cardiac function is not known. PURPOSE: The purpose was to examine the effects of endurance training on cardiac function in long-chain acyl-CoA dehy drogenase(L CAD -/-) and very-long-chain acyl-CoA dehydrogenase (VLCAD -/-) deficient mice. METHODS: Male mice were used and grouped as follows: 1) VLCAD -/-, non-exercised (n=8); 2)VLCAD -/-, exercised (n=6); 3) LCAD -/-, non-exercised (n=12); 4) LCAD -/-, exercised (n=6). Mice were trained by forced running on a treadmill for eight weeks. Twenty-four hours after the final exercise bout, the mice were anesthetized using 40 mg.Kg-1 sodium pentobarbital (i.p.) for determination of cardiac dimensions, fractional shortening, and ejection fraction using transthorasic echocardiography. Data were collected prior to and after injection with 20ng.g-1 isoproterenol and were analyzed using ANOVA of data in a 2 (training) × 2 (stress) factorial design. All comparisons were made at the 0.05 level of significance. RESULTS: Trained mice weighed significantly (p < 0.05) less than untrained mice. The weight for LCAD -/- mice tended to be higher than that of VLCAD -/- mice but not significantly. Trained mice and LCAD -/- mice had significantly (p < 0.05) larger heart weights. Training did not significantly affect cardiac dimensions. LCAD -/- mice had higher fractional shortening (FS) and a higher ejection fraction (EF). Isoproterenol improved FS% and EF with trained VLCAD -/- mice displaying a greater response. CONCLUSION: The results indicate that VLCAD deficiency caused a greater reduction in cardiac function but that the response of VLCAD -/- mice to exercise training was greater than that observed in LCAD -/- mice.

Effect of Orally Administered Oat ?-Glucan on the Macrophage Response to HSV-1 Infection Following Exercise Stress

Oat β-glucan (OβG), a soluble fiber with mild immunostimulant activity, can offset the increased risk of infection associated with exercise stress (Davis et. al., Med Sci Sports Exerc 36(8): 1321 −7, 2004). Macrophages (Mθs) play an important role in this mechanism: we have shown that depletion of Mθs negates the beneficial effect of OβG on preventing the exercise induced increase in susceptibility to infection (Murphy et. al., Med Sci Sports Exerc 37 (5); S128, 2005). Specifically, we have found that OβG can offset the decrease in intrinsic anti-viral resistance of Mθs associated with stressful exercise, however it is likely that extrinsic functions of Mθs are also involved. PURPOSE: To examine the effect of oral feedings of OβG on Mβ cytokine release following exercise stress and in vitro HSV-1 infection in mice. METHODS: Exercise mice (Ex-H2O & Ex-OβG) were run to fatigue on a treadmill for 3 consecutive days, control mice (Con-H2O & Con-OβG) remained in their cages in the treadmill room. OβG was fed to the mice in their drinking water for 10 consecutive days. Mice were sacrificed 15 minutes following the final exercise bout or rest. Lung and peritoneal Mθs were harvested via lavage, and allowed to adhere on a 96 well microplate at a concentration of 1 X 106. A standardized dose of HSV-1 was incubated with the Mθs for a period of 24h after which time supernatants were collected. Mβ supernatants were analyzed for IL-1β, IL-6 and TNF-α via ELISA. RESULTS: Both exercise and OβG increased IL-6 and TNF-α release from peritoneal and lung Mθs following HSV-1 infection. OβG increased IL-1β release from peritoneal Mθs following infection. RESULTS: indicate that both exercise and oral feedings OβG can increase the Mθ cytokine response to HSV-1 in vitro. CONCLUSION: The benefits of OβG on preventing the exercise induced increase in susceptibility to infection may be mediated at least in part by certain extrinsic functions of Mθs. This study was funded by a student research grant from the American College of Sports Medicine.

Exercise and improved insulin sensitivity in older women: evidence of the enduring benefits of higher intensity training

Few studies have compared the relative benefits of moderate- vs. higher intensity exercise training on improving insulin sensitivity in older people while holding exercise volume constant. Healthy older (73 +/- 10 yr) women (N = 25) who were inactive, but not obese, were randomized into one of three training programs (9-mo duration): 1) high-intensity [80% peak aerobic capacity (V(O2)peak); T(H)] aerobic training; 2) moderate-intensity (65% V(O2)peak; T(M)) aerobic training; or 3) low-intensity (stretching) placebo control (50% V(O2)peak); C(TB)). Importantly, exercise volume (300 kcal/session) was held constant for subjects in both the T(H) and the T(M) groups. V(O2)peak was determined by using a graded exercise challenge on a treadmill. Total body fat and lean mass were determined with dual-energy X-ray absorptiometry. The rate of insulin-stimulated glucose utilization as well as the suppression of lipolysis were determined approximately 72 h after the final exercise bout by using a two-step euglycemic-hyperinsulinemic clamp. We observed improved glucose utilization at the higher insulin dose with training, but these improvements were statistically significant only in the T(H) (21%; P = 0.02) compared with the T(M) (16%; P = 0.17) and C(TB) (8%; P = 0.37) groups and were observed without changes in either body composition or V(O2)peak. Likewise in the T(H) group, we detected a significant improvement in insulin-stimulated suppression (%) of adipose tissue lipolysis at the low-insulin dose (38-55%, P < 0.05). Our findings suggest that long-term higher intensity exercise training provides more enduring benefits to insulin action compared with moderate- or low-intensity exercise, likely due to greater transient effects.

Antioxidant enzyme activity is up-regulated after unilateral resistance exercise training in older adults

Cellular antioxidant capacity and oxidative stress are postulated to be critical factors in the aging process. The effects of resistance exercise training on the level of skeletal muscle oxidative stress and antioxidant capacity have not previously been examined in older adults. Muscle biopsies from both legs were obtained from the vastus lateralis muscle of 12 men 71 ± 7 years of age. Subjects then engaged in a progressive resistance exercise-training program with only one leg for 12 weeks. After 12 weeks, the nontraining leg underwent an acute bout of exercise (exercise session identical to that of the trained leg at the same relative intensity) at the same time as the last bout of exercise in the training leg. Muscle biopsies were collected from the vastus lateralis of both legs 48 h after the final exercise bout. Electron transport chain enzyme activity was unaffected by resistance training and acute resistance exercise ( p < 0.05). Training resulted in a significant increase in CuZnSOD (pre—7.2 ± 4.2, post—12.6 ± 5.6 U·mg protein −1; p = 0.02) and catalase (pre—8.2 ± 2.3, post—14.9 ± 7.6 μmol·min −1·mg protein −1; p = 0.02) but not MnSOD activity, whereas acute exercise had no effect on the aforementioned antioxidant enzyme activities. Furthermore, basal muscle total protein carbonyl content did not change as a result of exercise training or acute exercise. In conclusion, unilateral resistance exercise training is effective in enhancing the skeletal muscle cellular antioxidant capacity in older adults. The potential long-term benefits of these adaptations remain to be evaluated.

Effect of a Reduced Sampling Protocol on Changes in SI with Exercise Training

2267 Purpose: To determine if a reduced blood sampling protocol (13 samples) during an intravenous glucose tolerance test (IVGTT, minimal model analyses) altered the change in the insulin sensitivity index (SI) reported with exercise training. Methods: Thirty-one middle-aged men and women were examined before and after a 6-month exercise training program (50–70% of VO2peak, 3-5 days/wk, 40–60 min/day). An IVGTT was performed when the subjects were sedentary and 24 hours after the final exercise bout. Blood glucose and insulin were determined in the 33 samples obtained during a typical IVGTT and an SI calculated. Plasma insulin and glucose from the 13 samples recommended for a reduced sampling protocol were also utilized to calculate an SI and results compared. Results: SI increased significantly with training (mean ± SE) (P<0.001) when SI was calculated using either the 33- (3.1 ± 0.4 vs. 5.0 ± 0.6 (μU/L)−1 &#8729; min−1) or 13-sample (3.5 ± 0.6 vs. 4.9 ± 0.6 (μU/L)−1 &#8729; min−1) protocol. When comparing the relative change (post/pre) in SI with training, there was no difference between the 33- (1.6 ± 0.1-fold increase) and the 13-sample (1.6 ± 0.2- fold increase) methods. The two methods were related to each other (R=0.72, P<001). However, the minimal model program could not calculate an SI in 11 of the subjects with the 13 sample protocol. Conclusion: The 13-sample IVGTT method with use of the current minimal model program can provide accurate estimates of changes with training in some subjects.

EFFECTS OF EXERCISE DOSE AND DETRAINING ON LIPID LEVELS AND LIPOPROTEIN SUBFRACTIONS IN OVERWEIGHT ADULTS

It has recently been shown that aerobic exercise leads to widespread beneficial effects on lipoprotein levels and subfractions. However, it is unclear how long these benefits will be maintained during a detraining period and whether the amount and intensity of exercise performed prior to detraining plays a role in any sustained improvements. PURPOSE To determine the effects of different amounts and intensities of exercise on lipid levels and subfractions during a 14-day detraining period. METHODS 139 sedentary, overweight men and women (40–65 yrs.) with mild to moderate dyslipidemia [LDL > 130 and < 190 mg/dL or HDL < 40 mg/dL for men and < 45 mg/dL for women] were randomized into one of three exercise groups: 1) low [14 kcal/kg body weight/week at 40–55% VO2max], 2) moderate [14 kcal/kg/wk at 65–80% VO2max] or 3) high [23 kcal/kg/wk at 65–80% VO2max]. Subjects trained for ⁁8 months and were encouraged to maintain body weight. Fasting plasma samples were collected at three detraining time points: within 24 hours, five days and 14 days of the final exercise bout. RESULTS The high group had significant improvements in HDL cholesterol, large HDL and HDL size (p < 0.05) for all three time points compared to pre-training baseline. The low group maintained significant improvements in triglycerides. No significant, sustained improvements were seen in the moderate group. CONCLUSION The prolonged beneficial effects demonstrated by these data suggest a chronic adaptation due to exercise. Further research should examine the potential mechanism(s) of these sustained improvements. Supported by NIH Grant RO1 HL-57354.

SPLENIC CONTRACTION, CATECHOLAMINE RELEASE, AND BLOOD VOLUME REDISTRIBUTION DURING EXERCISE IN MAN

Purpose: To determine the mechanism for splenic volume reduction with exercise and to determine the effect of splenic expulsion of red cells on indirect plasma volume measurements. Methods: 9 males (age = 24.9 ± 1.0, VO2 max = 54.1 ± 2.3 ml.kg−1.min−1) undertook four exercise bouts. Three consisted of cycling at 60% VO2 max for 5, 10, and 15 minute duration, separated by 30 minutes. The final exercise bout was an incremental ride to exhaustion. Spleen imaging was determined using 99m Tc labeled red cells, immediately prior to and following each exercise bout as well as every ten minutes for an hour after the incremental ride. Plasma volume was measured with 125I-RISA pre- and 131I-RISA post-exercise, and 51 Cr was used to measure red cell volume. Plasma catecholamines were collected at rest and every 10 minutes for an hour following the incremental ride and analyzed by high performance liquid chromatography. Results: A significant reduction in spleen volume was observed following the durational rides (pre = 85.8 ± 10.1, post = 59.3 ± 8.1 mls; p < 0.001), however no significant differences were observed in the reduction in spleen volume between the three durational rides. Following the incremental ride to exhaustion the spleen volume was significantly reduced compared with pre-exercise at 0 and 10 minutes of recovery (pre = 85.9 ± 9.93, post 0 min = 36.4 ± 3.95, post 10 min = 61.9 ± 8.51 mls; p < 0.001). Spleen volume was inversely correlated with plasma epinephrine (r = −0.46; p < 0.001) and norepinephrine (r = −0.58; p < 0.001) following exercise. There was no significant difference in red cell or total blood volume pre- to post exercise, however a significant reduction in plasma volume was observed (pre = 46.6 ± 1.44, post = 38.3 ± 1.83 mls.kg−1; p = 0.002). There was no difference between the direct and indirect methods of assessing plasma volume reduction (I-RISA = 18.9 ± 2.41, Hct = 20.6 ± 1.90, Hb and Hct = 19.9 ± 1.83, Hb and Hct with F-cell correction = 17.3 ± 1.75%; p > 0.05). Conclusions: These results suggest that the spleen is capable of contracting in response to an intensity dependent signal and that plasma catecholamines are partially responsible. The release of red cells from the spleen appears to have no effect on indirect measures of plasma volume reduction. Supported by a grant from the British Columbia Sports Medicine Foundation

Interaction of exercise and diet on GLUT-4 protein and gene expression in Type I and Type II rat skeletal muscle.

We determined the interaction of exercise and diet on glucose transporter (GLUT-4) protein and mRNA expression in type I (soleus) and type II [extensor digitorum longus (EDL)] skeletal muscle. Forty-eight Sprague Dawley rats were randomly assigned to one of two dietary conditions: high-fat (FAT, n=24) or high-carbohydrate (CHO, n=24). Animals in each dietary condition were allocated to one of two groups: control (NT, n=8) or a group that performed 8 weeks of treadmill running (4 sessions week-1 of 1000 m @ 28 m min-1, RUN, n=16). Eight trained rats were killed after their final exercise bout for determination of GLUT-4 protein and mRNA expression: the remainder were killed 48 h after their last session for measurement of muscle glycogen and triacylglycerol concentration. GLUT-4 protein expression in NT rats was similar in both muscles after 8 weeks of either diet. However, there was a main effect of training such that GLUT-4 protein was increased in the soleus of rats fed with either diet (P < 0.05) and in the EDL in animals fed with CHO (P < 0.05). There was a significant diet-training interaction on GLUT-4 mRNA, such that expression was increased in both the soleus (100% upward arrowP < 0.05) and EDL (142% upward arrowP < 0.01) in CHO-fed animals. Trained rats fed with FAT decreased mRNA expression in the EDL ( downward arrow 45%, P < 0.05) but not the soleus ( downward arrow 14%, NS). We conclude that exercise training in CHO-fed rats increased both GLUT-4 protein and mRNA expression in type I and type II skeletal muscle. Despite lower GLUT-4 mRNA in muscles from fat-fed animals, exercise-induced increases in GLUT-4 protein were largely preserved, suggesting that control of GLUT-4 protein and gene expression are modified independently by exercise and diet.

Effect of endurance exercise on myosin heavy chain gene regulation in human skeletal muscle.

The purpose of this study was to determine the effect of endurance-oriented exercise on myosin heavy chain (MHC) isoform regulation in human skeletal muscle. Exercise consisted of 1 h of cycle ergometer work per day at 75% maximal oxygen consumption for seven consecutive days. Muscle was obtained before the first bout of exercise, 3 h after the first bout of exercise, and before and 3 h after the final exercise bout on day 7 (n = 9 subjects). No changes in MHC mRNA (I, IIa, IIx) were evident after the first exercise period. There was, however, a significant (P < 0.05) decline (-30%) in MHC IIx mRNA 3 h after the final training bout. An interesting finding was that a higher pretraining level of MHC IIx mRNA was associated with a greater decline in the transcript before (r = 0.68, P < 0.05) and 3 h after (r = 0.82, P < 0.05) the final exercise bout. These findings suggest that MHC IIx mRNA is downregulated during the early phase of endurance-oriented exercise training in human skeletal muscle but only after repeated contractile activity. Pretraining MHC IIx mRNA content may influence the magnitude of this response.

EFFECT OF 7 DAYS OF EXERCISE TRAINING ON INSULIN ACTION IN YOUNG VERSUS AGED SUBJECTS 67

The goal of this research was to determine if acute, exercise training increased insulin action to the same degree in young versus aged individuals. Subjects tested were 1) young men (mean ± SE, 20.9 ± 0.9 yrs; n=9); 2) young women (22.4 ± 0.8 yrs; n=9);3) aged men (56.5 ± 1.9 yrs; n=8); and 4) post-menopausal women (60.9 ± 1.0; n=10). Subjects trained on a cycle ergometer for 60 min/day at 75% VO2max for 7 days. Insulin action(SI) was determined with an intravenous glucose tolerance test 14-16 hours after the final exercise bout. Initial comparisons indicated a significant (P<0.05) gender effect for SI; data were thus compared within each gender. Exercise improved (P<0.01) SI in the young and aged men by 1.4 and 1.8 fold, respectively. The aged men were, however, significantly (P<0.05) more insulin resistant than their young counterparts before and after training. There was no age effect on SI in the women; both groups improved significantly(P<0.001) by ≅1.8-fold with training. There was a trend for first-phase insulin secretion to improve in the aged groups and not change in the young groups with training. These data indicate that 7 days of exercise training improves insulin action by a similar increment in both young and aged subjects; aged men, however, are relatively insulin resistant.

Time course for exercise-induced alterations in insulin action and glucose tolerance in middle-aged people

The purposes of this study were 1) to investigate glucose tolerance and insulin action immediately after exercise and 2) to determine how long the improved glucose homeostatic mechanisms observed 12-16 h after exercise persist. Nine (seven men, two women) moderately trained middle-aged (51 +/- 3 yr) subjects performed 45 min of exercise at 73 +/- 2% of peak O2 uptake for 5 days, followed by 7 days of inactivity. Oral glucose tolerance tests (OGTT; 75 g) were performed immediately postexercise (IPE; approximately 30 min) after the final exercise bout and 1, 3, 5, and 7 days after exercise. The incremental area under the plasma glucose curve was markedly higher IPE (355 +/- 82 mM.min) compared with those on days 1 (136 +/- 57 mM.min; P < 0.05) and 3 (173 +/- 62 mM.min; P < 0.05). The glucose area was significantly higher on days 5 (213 +/- 80 mM.min) and 7 (225 +/- 84 mM.min) compared with those on days 1 and 3 (P < 0.05). The incremental insulin area IPE (3,729 +/- 1,104 microU.ml-1.min) was 43% higher compared with that on day 1 (2,603 +/- 635 microU.ml-1.min; P < 0.05) and 66% higher compared with that on day 3 (2,240 +/- 517 microU.ml-1.min; P < 0.05). The insulin area increased to 3,616 +/- 617 microU.ml-1.min after 5 days of inactivity (P < 0.05). An additional 48 h of inactivity did not result in any further increase in the plasma insulin response.(ABSTRACT TRUNCATED AT 250 WORDS)

Physical training and connective tissues in young mice. Biochemistry of skin.

The effect of physical training on some connective tissue components of the skin was studied in male mice of NMRI-strain. The mice to be trained and their controls were about 2-weeks-old at the beginning of the training, which took place on a 5 degree inclined treadmill 5 days a week for 3-22 weeks progressively. The final exercise bouts were 50 and 80 min for moderate programmes and 180 min for the intensive programme at a speed of 30 cm/s. At the end of each experiment skin samples from trained and control animals were taken for the analyses. We found increased concentrations of nitrogen, hexosamines and hydroxyproline in the skin of the trained mice compared to the controls. The unchanged DNA concentration suggests that the activation of synthesis occurred in a constant number of cells.

Physical training and connective tissues in young mice-heart.

The effect of physical training on the chemical properties of the heart tissues was studied in male mice of NMRI-strain. The mice to be trained and their controls were about 2 weeks old at the beginning of the training, which took place on 5 degrees inclined treadmill 5 days a week for 3-22 weeks. The duration of daily exercise was progressively increased over the first 3 weeks. The final daily exercise bouts were 50 and 80 min for moderate programs and 180 min for the intensive program at a speed of 30 cm/s. The whole heart or the ventricles were used for the analyses. We found no significant changes related to training in the concentrations of nitrogen, hexosamines, and hydroxyproline both in the normal-sized and the hypertrophied hearts. The hydroxyproline concentration of the ventricles was lower than that of the whole heart tissue, but no difference was observed in the concentration of nitrogen. The hydroxyproline concentration of the heart tissue increased with age both in the trained and untrained mice (39% over 19 weeks). We conclude that collagen and non-collagen proteins in the heart tissue of young mice are stimulated in equal proportions by physical training.