Endurance training reduces the contraction-induced interleukin-6 mRNA expression in human skeletal muscle

Contracting skeletal muscle expresses large amounts of IL-6. Because 1) IL-6 mRNA expression in contracting skeletal muscle is enhanced by low muscle glycogen content, and 2) IL-6 increases lipolysis and oxidation of fatty acids, we hypothesized that regular exercise training, associated with increased levels of resting muscle glycogen and enhanced capacity to oxidize fatty acids, would lead to a less-pronounced increase of skeletal muscle IL-6 mRNA in response to acute exercise. Thus, before and after 10 wk of knee extensor endurance training, skeletal muscle IL-6 mRNA expression was determined in young healthy men (n = 7) in response to 3 h of dynamic knee extensor exercise, using the same relative workload. Maximal power output, time to exhaustion during submaximal exercise, resting muscle glycogen content, and citrate synthase and 3-hydroxyacyl-CoA dehydrogenase enzyme activity were all significantly enhanced by training. IL-6 mRNA expression in resting skeletal muscle did not change in response to training. However, although absolute workload during acute exercise was 44% higher (P < 0.05) after the training period, skeletal muscle IL-6 mRNA content increased 76-fold (P < 0.05) in response to exercise before the training period, but only 8-fold (P < 0.05, relative to rest and pretraining) in response to exercise after training. Furthermore, the exercise-induced increase of plasma IL-6 (P < 0.05, pre- and posttraining) was not higher after training despite higher absolute work intensity. In conclusion, the magnitude of the exercise-induced IL-6 mRNA expression in contracting human skeletal muscle was markedly reduced by 10 wk of training.     

The effects of exercise-induced muscle damage on cycling time-trial performance

Previous research has advocated that plyometric training improves endurance performance. However, a consequence of such a training is the immediate and prolonged appearance of exercise-induced muscle damage (EIMD). This study examined whether a single bout of plyometric exercise, designed to elicit muscle damage, affected cycling endurance performance. Seventeen participants were randomly assigned to either a muscle damage (n = 7 men, 1 woman) or nonmuscle damage (n = 8 men, 1 woman) group. Before and at 48 hours, participants were measured for perceived muscle soreness, peak isokinetic strength, and physiological, metabolic, and perceptual responses during 5-minute submaximal cycling at ventilatory threshold (VT) and a 15-minute time trial. Perceived muscle soreness and isokinetic strength (p < 0.05) were significantly altered in the muscle damage group after EIMD. No changes in heart rate or blood lactate were evident during submaximal exercise (p > 0.05). However, VO2, V(E), and rating of perceived exertion (RPE) values were increased at VT in the muscle damage group at 48 hours after EIMD (p < 0.05). During the time trial, mean power output, distance covered, and VO2 were lower in the muscle damage group at 48 hours after EIMD (p < 0.05). However, there was no change in RPE (p > 0.05), suggesting effort perception was unchanged during time-trial performance after EIMD. In conclusion, individuals using concurrent plyometric and endurance training programs to improve endurance performance should be aware of the acute impact of muscle-damaging exercise on subsequent cycling performance.     

Antioxidant supplementation prevents exercise-induced lipid peroxidation, but not inflammation, in ultramarathon runners

To determine if 6 weeks of supplementation with vitamins E and C could alleviate exercise-induced lipid peroxidation and inflammation, we studied 22 runners during a 50 km ultramarathon. Subjects were randomly assigned to one of two groups: (1) placebos (PL) or (2) antioxidants (AO: 1000 mg vitamin C and 300 mg RRR-alpha-tocopheryl acetate). Blood samples were obtained prior to supplementation (baseline), after 3 weeks of supplementation, 1 h pre-, mid-, and postrace, 2 h postrace and for 6 days postrace. Plasma levels of alpha-tocopherol (alpha-TOH), ascorbic acid (AA), uric acid (UA), F2-isoprostanes (F2-IsoPs), tumor necrosis factor alpha (TNF-alpha), interleukin-6 (IL-6), and C-reactive protein (CRP) were measured. With supplementation, plasma alpha-TOH and AA increased in the AO but not the PL group. Although F2-IsoP levels were similar between groups at baseline, 28 +/- 2 (PL) and 27 +/- 3 pg/ml (AO), F2-IsoPs increased during the run only in the PL group (41 +/- 3 pg/ml). In PL women, F2-IsoPs were elevated postrace (p <.01), but returned to prerace concentrations by 2 h postrace. In PL men, F2-IsoP concentrations were higher postrace, 2 h postrace, and 1, 2, 3, 4, and 6 days postrace (PL vs. AO group, each p <.03). Markers of inflammation were increased dramatically in response to the run regardless of treatment group. Thus, AO supplementation prevented endurance exercise-induced lipid peroxidation but had no effect on inflammatory markers.     

Effect of antioxidant supplementation on insulin sensitivity in response to endurance exercise training

While production of reactive oxygen and nitrogen species (RONS) is associated with some of the beneficial adaptations to regular physical exercise, it is not established whether RONS play a role in the improved insulin-stimulated glucose uptake in skeletal muscle obtained by endurance training. To assess the effect of antioxidant supplementation during endurance training on insulin-stimulated glucose uptake, 21 young healthy (age 29 ± 1 y, BMI 25 ± 3 kg/m(2)) men were randomly assigned to either an antioxidant [AO; 500 mg vitamin C and 400 IU vitamin E (α-tocopherol) daily] or a placebo (PL) group that both underwent a supervised intense endurance-training program 5 times/wk for 12 wk. A 3-h euglycemic-hyperinsulinemic clamp, a maximal oxygen consumption (Vo(2max)) and maximal power output (P(max)) test, and body composition measurements (fat mass, fat-free mass) were performed before and after the training. Muscle biopsies were obtained for determination of the concentration and activity of proteins regulating glucose metabolism. Although plasma levels of vitamin C (P < 0.05) and α-tocopherol (P < 0.05) increased markedly in the AO group, insulin-stimulated glucose uptake increased similarly in both the AO (17.2%, P < 0.05) and the PL (18.9%, P < 0.05) group in response to training. Vo(2max) and P(max) also increased similarly in both groups (time effect, P < 0.0001 for both) as well as protein content of GLUT4, hexokinase II, and total Akt (time effect, P ≤ 0.05 for all). Our results indicate that administration of antioxidants during strenuous endurance training has no effect on the training-induced increase in insulin sensitivity in healthy individuals.     

Vitamin E isoform-specific inhibition of the exercise-induced heat shock protein 72 expression in humans.

Increased levels of reactive oxygen and nitrogen species, as seen in response to exercise, challenge the cellular integrity. Important protective adaptive changes include induction of heat shock proteins (HSPs). We hypothesized that supplementation with antioxidant vitamins C (ascorbic acid) and E (tocopherol) would attenuate the exercise-induced increase of HSP72 in the skeletal muscle and in the circulation. Using randomization, we allocated 21 young men into three groups receiving one of the following oral supplementations: RRR-alpha-tocopherol 400 IU/day + ascorbic acid (AA) 500 mg/day (CEalpha), RRR-alpha-tocopherol 290 IU/day + RRR-gamma-tocopherol 130 IU/day + AA 500 mg/day (CEalphagamma), or placebo (Control). After 28 days of supplementation, the subjects performed 3 h of knee extensor exercise at 50% of the maximal power output. HSP72 mRNA and protein content was determined in muscle biopsies obtained from vastus lateralis at rest (0 h), postexercise (3 h), and after a 3-h recovery (6 h). In addition, blood was sampled for measurements of HSP72, alpha-tocopherol, gamma-tocopherol, AA, and 8-iso-prostaglandin-F2alpha (8-PGF2alpha). Postsupplementation, the groups differed with respect to plasma vitamin levels. The marker of lipid peroxidation, 8-iso-PGF2alpha, increased from 0 h to 3 h in all groups, however, markedly less (P < 0.05) in CEalpha. In Control, skeletal muscle HSP72 mRNA content increased 2.5-fold (P < 0.05) and serum HSP72 protein increased 4-fold (P < 0.05) in response to exercise, whereas a significant increase of skeletal muscle HSP72 protein content was not observed (P = 0.07). In CEalpha, skeletal muscle HSP72 mRNA, HSP72 protein, and serum HSP72 were not different from Control in response to exercise. In contrast, the effect of exercise on skeletal muscle HSP72 mRNA and protein, as well as circulating HSP72, was completely blunted in CEalphagamma. The results indicate that gamma-tocopherol comprises a potent inhibitor of the exercise-induced increase of HSP72 in skeletal muscle as well as in the circulation.     

Effect of vitamin supplementation on cytokine response and on muscle damage after strenuous exercise

The present double-blinded, placebo-controlled study investigated whether antioxidant vitamin supplementation was able to modulate the cytokine and lymphocyte responses after strenuous eccentric exercise. Furthermore, muscle enzyme release was examined to see whether antioxidant treatment could reduce muscle damage. Twenty male recreational runners randomly received either antioxidants (500 mg of vitamin C and 400 mg of vitamin E) or placebo for 14 days before and 7 days after a 5% downhill 90-min treadmill run at 75% .VO(2 max). Although the supplemented group differed significantly with regard to plasma vitamin concentration before and after exercise when compared with the placebo group, the two groups showed identical exercise-induced changes in cytokine, muscle enzyme, and lymphocyte subpopulations. The plasma level of interleukin (IL)-6 and IL-1 receptor antagonist increased 20- and 3-fold after exercise. The plasma level of creatine kinase was increased sixfold the day after exercise. The concentrations of CD4+ memory T cells, CD8+ memory and na?ve T cells, and natural killer cells increased at the end of exercise. The total lymphocyte concentration was below prevalues in the postexercise period. In conclusion, the present study does not support the idea that exercise-induced inflammatory responses are induced by free oxygen radicals.     

Glutamine supplementation further enhances exercise-induced plasma IL-6.

Exercise stimulates the production and release of interleukin-6 (IL-6) from skeletal muscle. Glutamine is also synthesized in skeletal muscle and is involved in protein synthesis within this tissue. During exercise, plasma levels of glutamine decline, and this may affect the concentration of plasma IL-6 via a decrease in IL-6 synthesis and release from muscle. We hypothesized that glutamine supplementation would attenuate the exercise-induced decrease in plasma glutamine concentration and, thus, further enhance levels of plasma IL-6. Eight healthy men participated in a randomized, double-blind, crossover study in which they performed 2 h of cycle ergometry at 75% of peak O2 uptake. They received glutamine, glutamine-rich protein, or placebo supplementation at intervals during and 2 h after exercise. Exercise induced an 11-fold increase in plasma IL-6, which was further enhanced by glutamine (18-fold) and glutamine-rich protein (14-fold) supplementation, administered at doses that attenuated the exercise-induced decrease in plasma glutamine concentration.     

Visfatin mRNA expression in human subcutaneous adipose tissue is regulated by exercise

Visfatin [pre-beta-cell colony-enhancing factor (PBEF)] is a novel adipokine that is produced by adipose tissue, skeletal muscle, and liver and has insulin-mimetic actions. Regular exercise enhances insulin sensitivity. In the present study, we therefore examined visfatin mRNA expression in abdominal subcutaneous adipose tissue and skeletal muscle biopsies obtained from healthy young men at time points 0, 3, 4.5, 6, 9, and 24 h in relation to either 3 h of ergometer cycle exercise at 60% of Vo(2 max) or rest. Adipose tissue visfatin mRNA expression increased threefold at the time points 3, 4.5, and 6 h in response to exercise (n = 8) compared with preexercise samples and compared with the resting control group (n = 7, P = 0.001). Visfatin mRNA expression in skeletal muscle was not influenced by exercise. The exercise-induced increase in adipose tissue visfatin was, however, not accompanied by elevated levels of plasma visfatin. Recombinant human IL-6 infusion to mimic the exercise-induced IL-6 response (n = 6) had no effect on visfatin mRNA expression in adipose tissue compared with the effect of placebo infusion (n = 6). The finding that exercise enhances subcutaneous adipose tissue visfatin mRNA expression suggests that visfatin has a local metabolic role in the recovery period following exercise.     

Effects of beta-hydroxy-beta-methylbutyrate on muscle damage after a prolonged run.

This study examined the effects of supplemental beta-hydroxy-beta-methylbutyrate (HMB) on muscle damage as a result of intense endurance exercise. Subjects (n = 13) were paired according to their 2-mile run times and past running experience. Each pair was randomly assigned a treatment of either HMB (3 g/day) or a placebo. After 6 wk of daily training and supplementation, all subjects participated in a prolonged run (20-km course). Creatine phosphokinase and lactate dehydrogenase (LDH) activities were measured before and after a prolonged run to assess muscle damage. The placebo-supplemented group exhibited a significantly greater (treatment main effect, P = 0.05) increase in creatine phosphokinase activity after a prolonged run than did the HMB-supplemented group. In addition, LDH activity was significantly lower (treatment main effect, P = 0.003) with HMB supplementation compared with the placebo-supplemented group. In conclusion, supplementation with 3.0 g of HMB results in a decreased creatine phosphokinase and LDH response after a prolonged run. These findings support the hypothesis that HMB supplementation helps prevent exercise-induced muscle damage.     

Quercetin's influence on exercise-induced changes in plasma cytokines and muscle and leukocyte cytokine mRNA.

Trained male cyclists (n = 40) ingested quercetin (Q; n = 20) (1,000 mg/day) or placebo (P; n = 20) supplements under randomized, double-blinded methods for 3 wk before and during a 3-day period in which subjects cycled for 3 h/day at approximately 57% maximal work rate. Blood samples were collected before and after each exercise session and assayed for plasma IL-6, IL-10, IL-1ra, IL-8, TNF-alpha, and monocyte chemoattractant protein 1, and leukocyte IL-10, IL-8, and IL-1ra mRNA. Muscle biopsies were obtained before and after the first and third exercise sessions and assayed for NF-kappaB and cyclooxygenase-2 (COX-2), IL-6, IL-8, IL-1beta, and TNF-alpha mRNA. Postexercise increases in plasma cytokines did not differ between groups, but the pattern of change over the 3-day exercise period tended to be lower in Q vs. P for IL-8 and TNF-alpha (P = 0.094 for both). mRNA increased significantly postexercise for each cytokine measured in blood leukocyte and muscle samples. Leukocyte IL-8 and IL-10 mRNA were significantly reduced in Q vs. P (interaction effects, P = 0.019 and 0.012, respectively) with no other leukocyte or muscle mRNA group differences. Muscle NF-kappaB did not increase postexercise and did not differ between Q and P. Muscle COX-2 mRNA increased significantly postexercise but did not differ between Q and P. In summary, 1 g/day quercetin supplementation by trained cyclists over a 24-day period diminished postexercise expression of leukocyte IL-8 and IL-10 mRNA, indicating that elevated plasma quercetin levels exerted some effects within the blood compartment. Quercetin did not, however, influence any of the muscle measures, including NF-kappaB content, cytokine mRNA, or COX-2 mRNA expression across a 3-day intensified exercise period.     

Increased fatigue resistance of respiratory muscles during exercise after respiratory muscle endurance training

Respiratory muscle fatigue develops during exhaustive exercise and can limit exercise performance. Respiratory muscle training, in turn, can increase exercise performance. We investigated whether respiratory muscle endurance training (RMT) reduces exercise-induced inspiratory and expiratory muscle fatigue. Twenty-one healthy, male volunteers performed twenty 30-min sessions of either normocapnic hyperpnoea (n = 13) or sham training (CON, n = 8) over 4-5 wk. Before and after training, subjects performed a constant-load cycling test at 85% maximal power output to exhaustion (PRE(EXH), POST(EXH)). A further posttraining test was stopped at the pretraining duration (POST(ISO)) i.e., isotime. Before and after cycling, transdiaphragmatic pressure was measured during cervical magnetic stimulation to assess diaphragm contractility, and gastric pressure was measured during thoracic magnetic stimulation to assess abdominal muscle contractility. Overall, RMT did not reduce respiratory muscle fatigue. However, in subjects who developed >10% of diaphragm or abdominal muscle fatigue in PRE(EXH), fatigue was significantly reduced after RMT in POST(ISO) (inspiratory: -17 +/- 6% vs. -9 +/- 10%, P = 0.038, n = 9; abdominal: -19 +/- 10% vs. -11 +/- 11%, P = 0.038, n = 9), while sham training had no significant effect. Similarly, cycling endurance in POST(EXH) did not improve after RMT (P = 0.071), while a significant improvement was seen in the subgroup with >10% of diaphragm fatigue after PRE(EXH) (P = 0.017), but not in the sham training group (P = 0.674). However, changes in cycling endurance did not correlate with changes in respiratory muscle fatigue. In conclusion, RMT decreased the development of respiratory muscle fatigue during intensive exercise, but this change did not seem to improve cycling endurance.     

Vitamin E inhibits protein oxidation in skeletal muscle of resting and exercised rats.

It is well known that exercise induces lipid peroxidation in skeletal muscle and that vitamin E prevents exercise-induced lipid damage. In this study we show for the first time, an increase in protein oxidation in skeletal muscle after a single bout of exercise, related to an exercise-induced decrease in lipophilic antioxidants, and substantial protection against both resting and exercise-induced protein oxidation by supplementation with various isomers (alpha-tocopherol, alpha-tocotrienol) of vitamin E.     

Vitamin E deficiency and vitamin C supplements: exercise and mitochondrial oxidation

The effects of dietary antioxidant vitamins E and C on exercise endurance capacity and mitochondrial oxidation were investigated in rats. The endurance capacity of both vitamin E-deficient and vitamin C-supplemented, E-deficient rats was significantly (P less than 0.05) lower (38.1 and 33.6%, respectively) than control animals. Compared with the normal and vitamin E-deficient rats, there was a significant (P less than 0.05) increase in the concentration of vitamin C in blood and liver of the vitamin E-deficient, C-supplemented animals. Hence dietary vitamin C supplementation does not prevent the inhibition of exercise endurance capacity or increased hemolysis seen in vitamin E deficiency. The mitochondrial activities for the oxidation of palmitoyl carnitine and alpha-ketoglutarate were significantly (P less than 0.05) decreased by a single bout of exercise in brown adipose tissue but not in muscle, heart, or liver from vitamin C-supplemented, E-deficient groups of rats when compared with the activities in the tissue from the same group of rats killed at rest. Similar results were also seen in brown adipose tissue from vitamin E-deficient rats. The results suggest a tissue-specific role for vitamins E and C in substrate oxidation and show that the poor endurance capacity of vitamin E-deficient rats cannot be attributed to any changes in the mitochondrial activity in skeletal or cardiac muscles. It is also concluded that vitamin C supplementation, at least at the dose employed in the present study, cannot counteract the detrimental effects associated with vitamin E deficiency.     

Effects of creatine supplementation and exercise training on fitness in men 55-75 yr old.

effect of oral creatine supplementation (CR; 5 g/day) in conjunction with exercise training on physical fitness was investigated in men between 55 and 75 yr of age (n = 46). A double-blind randomized placebo-controlled (PL) trial was performed over a 6-mo period. Furthermore, a subgroup (n = 20) completed a 1-yr follow-up. The training program consisted of cardiorespiratory endurance training as well as moderate resistance training (2-3 sessions/wk). Endurance capacity was evaluated during a maximal incremental bicycle ergometer test, maximal isometric strength of the knee-extensor muscles was assessed by an isokinetic dynamometer, and body composition was assessed by hydrostatic weighing. Furthermore, in a subgroup (PL: n = 13; CR: n = 12) biopsies were taken from m. vastus lateralis to determine total creatine (TCr) content. In PL, 6 mo of training increased peak oxygen uptake rate (+16%; P < 0.05). Fat-free mass slightly increased (+0.3 kg; P < 0.05), whereas percent body fat slightly decreased (-1.2%; P < 0.05). The training intervention did not significantly change either maximal isometric strength or body weight. The responses were independent of CR. Still, compared with PL, TCr was increased by approximately 5% in CR, and this increase was closely correlated with initial muscle creatine content (r = -0.78; P < 0.05). After a 1-yr follow-up, muscle TCr was not higher in CR than in PL. Furthermore, the other measurements were not affected by CR. It is concluded that long-term creatine intake (5 g/day) in conjunction with exercise training does not beneficially impact physical fitness in men between 55 and 75 yr of age.     

Elevated muscle vitamin E does not attenuate eccentric exercise-induced muscle injury.

The purpose of this study was to evaluate the effect of elevated muscle vitamin E content on skeletal muscle damage from eccentric exercise. Sixty Sprague-Dawley rats were put on a normal (40 IU vitamin E/kg food) or supplemented (10,000 IU vitamin E/kg food) diet for 5 wk. Injury in soleus muscle was determined using several criteria: reductions in maximal tetanic force and number of intact fibers per square millimeter and elevations in muscle glucose 6-phosphate dehydrogenase activity and plasma creatine kinase activity, either immediately (0 h) or 2 days (48 h) after a downhill walking protocol. Sedentary animals were also tested but did not exercise. Muscle vitamin E levels were significantly elevated (approximately 3- to 4-fold), and susceptibility of the muscles to oxidant stress was decreased, after supplementation. However, vitamin E supplementation did not attenuate injury by any of the criteria employed. Maximal tetanic force decreased approximately 20% at 0 and 48 h after exercise in both groups. The number of intact fibers per square millimeter decreased approximately 30-35% in both groups at 0 and 48 h. Glucose 6-phosphate dehydrogenase activity increased approximately 50-100% in both groups at 48 h, and plasma creatine kinase activity was elevated approximately 2- to 2.5-fold at 0 h in both groups. These findings do not support a major role for free radical damage to muscle membranes in the initiation of injury from eccentric exercise, although they do not disprove free radical involvement in the etiology.     

Creatine supplementation reduces oxidative stress biomarkers after acute exercise in rats

The objective of this study was to evaluate the effect of creatine supplementation on muscle and plasma markers of oxidative stress after acute aerobic exercise. A total of 64 Wistar rats were divided into two groups: control group (n = 32) and creatine-supplemented group (n = 32). Creatine supplementation consisted of the addition of 2% creatine monohydrate to the diet. After 28 days, the rats performed an acute moderate aerobic exercise bout (1-h swimming with 4% of total body weight load). The animals were killed before (pre) and at 0, 2 and 6 h (n = 8) after acute exercise. As expected, plasma and total muscle creatine concentrations were significantly higher (P < 0.05) in the creatine-supplemented group compared to control. Acute exercise increased plasma thiobarbituric acid reactive species (TBARS) and total lipid hydroperoxide. The same was observed in the soleus and gastrocnemius muscles. Creatine supplementation decreased these markers in plasma (TBARS: pre 6%, 0 h 25%, 2 h 27% and 6 h 20%; plasma total lipid hydroperoxide: pre 38%, 0 h 24%, 2 h 12% and 6 h 20%, % decrease). Also, acute exercise decreased the GSH/GSSG ratio in soleus muscle, which was prevented by creatine supplementation (soleus: pre 8%, 0 h 29%, 2 h 30% and 6 h 44%, % prevention). The results show that creatine supplementation inhibits increased oxidative stress markers in plasma and muscle induced by acute exercise.