Single Bout Of Intense Exercise Research Articles

Acidosis attenuates CPT-I-supported bioenergetics as a potential mechanism limiting lipid oxidation

Fuel interactions in contracting muscle represent a complex interplay between enzymes regulating carbohydrate and fatty acid catabolism, converging in the mitochondrial matrix. While increasing exercise intensity promotes carbohydrate use at the expense of fatty acid oxidation, the mechanisms underlying this effect remain poorly elucidated. As a potential explanation, we investigated whether exercise-induced reductions in intramuscular pH (acidosis) attenuate carnitine palmitoyltransferase-I (CPT-I)-supported bioenergetics, the rate-limiting step for fatty acid oxidation within mitochondria. Specifically, we assessed the effect of a physiologically relevant reduction in pH (pH 7.2 versus 6.8) on single and mixed substrate respiratory responses in murine skeletal muscle isolated mitochondria and permeabilized fibers. While pH did not influence oxidative phosphorylation stoichiometry (ADP/O ratios), coupling efficiency, oxygen affinity, or ADP respiratory responses, acidosis impaired lipid bioenergetics by attenuating respiration with L-carnitine and palmitoyl-CoA, while enhancing the inhibitory effect of malonyl-CoA on CPT-I. These acidotic effects were largely retained following a single bout of intense exercise. At rest, pyruvate and succinate-supported respiration were also impaired by acidosis. However, providing more pyruvate and ADP at pH 6.8 to model increases in glycolytic flux and ATP turnover with intense exercise overcame the acidotic attenuation of carbohydrate-linked oxidative phosphorylation. Importantly, this situation is fundamentally different from lipids where CPT-I substrate sensitivity and availability is impaired at higher power outputs suggesting lipid metabolism may be more susceptible to the effects of acidosis, possibly contributing to fuel shifts with increasing exercise intensity.

The effect of exercise on cytokine concentration in equine autologous conditioned serum.

Autologous conditioned serum (ACS) is a commonly administered intra-articular treatment for the management of osteoarthritis in athletic horses. To investigate the influence of exercise on the concentration of cytokines in a non-commercial method of ACS production. Non-randomised cross over design. Whole blood was obtained from eight healthy Standardbred horses immediately prior to, 1h and 24 h following a single bout of exhaustive exercise. Blood was processed using a non-commercial method of ACS production. Fluorescent microsphere immunoassay (FMIA) analysis was performed to quantify Interleukin 1 receptor antagonist (IL-1Ra), Interleukin-10 (IL-10), Interleukin 1β (IL-1β) and tumour necrosis factor α (TNF-α) concentrations at each time point. Mixed effect repeated measures analysis of variance (ANOVA) was used to compare the pre-exercise and post-exercise cytokine concentrations. Significance was set at P < 0.05. A reduced concentration of IL-1Ra (median 584.4, IQR 81.9-5098 pg/ml, p= 0.004) and an increased concentration of TNF-α (11.92, 9.28-39.75 pg/ml, P= .05) at 1h post-exercise were observed when compared with baseline values (IL-Ra 7349, 1272-10760 pg/ml; TNF TNF-α 11.16, 8.36-32.74 pg/ml). No difference in cytokine concentrations of IL-10 or IL-1β were found between any of the time points. The large biological variability and small sample size represents limitations of this study. These results suggest that a single bout of intense exercise can reduce the concentration of the anti-inflammatory cytokine IL-1Ra and increase the concentration of the pro-inflammatory cytokine TNF-α, reducing the 'anti-inflammatory' cytokine composition of ACS. Our findings suggest that collection of blood for ACS production should be performed no sooner than 24 h following a single episode of intense exercise.

Effect of ubiquinol supplementation on biochemical and oxidative stress indexes after intense exercise in young athletes

ABSTRACTObjectives: Physical exercise significantly impacts the biochemistry of the organism. Ubiquinone is a key component of the mitochondrial respiratory chain and ubiquinol, its reduced and active form, is an emerging molecule in sport nutrition. The aim of this study was to evaluate the effect of ubiquinol supplementation on biochemical and oxidative stress indexes after an intense bout of exercise.Methods: 21 male young athletes (26 + 5 years of age) were randomized in two groups according to a double blind cross-over study, either supplemented with ubiquinol (200 mg/day) or placebo for 1 month. Blood was withdrawn before and after a single bout of intense exercise (40 min run at 85% maxHR). Physical performance, hematochemical parameters, ubiquinone/ubiquinol plasma content, intracellular reactive oxygen species (ROS) level, mitochondrial membrane depolarization, paraoxonase activity and oxidative DNA damage were analyzed.Results: A single bout of intense exercise produced a significant increase in most hematochemical indexes, in particular CK and Mb while, on the contrary, normalized coenzyme Q10 plasma content decreased significantly in all subjects. Ubiquinol supplementation prevented exercise-induced CoQ deprivation and decrease in paraoxonase activity. Moreover at a cellular level, in peripheral blood mononuclear cells, ubiquinol supplementation was associated with a significant decrease in cytosolic ROS while mitochondrial membrane potential and oxidative DNA damage remained unchanged.Discussion: Data highlights a very rapid dynamic of CoQ depletion following intense exercise underlying an increased demand by the organism. Ubiquinol supplementation minimized exercise-induced depletion and enhanced plasma and cellular antioxidant levels but it was not able to improve physical performance indexes or markers of muscular damage.

Enhancing consolidation of a rotational visuomotor adaptation task through acute exercise.

We assessed the effect of a single bout of intense exercise on the adaptation and consolidation of a rotational visuomotor task, together with the effect of the order of exercise presentation relative to the learning task. Healthy adult participants (n = 29) were randomly allocated to one of three experimental groups: (1) exercise before task practice, (2) exercise after task practice, and (3) task practice only. After familiarization with the learning task, participants undertook a baseline practice set. Then, four 60° clockwise rotational sets were performed, comprising an adaptation set and three retention sets at 1 h, 24 h, and 7 days after the adaptation set. Depending on the experimental group, exercise was presented before or after the adaptation sets. We found that error reduction during adaptation was similar regardless of when exercise was presented. During retention, significant error reduction was found in the retention set at 1 h for both exercise groups, but this enhancement was not present during subsequent retention sets, with no differences present between exercise groups. We conclude that an acute bout of intense exercise could positively affect retention, although the order in which exercise is presented does not appear to influence its benefits during the early stages of consolidation.

Oxidative Stress and Antioxidant Status in Standardbreds: Effect of Age and Acute Exercise Before and After Training

The hypothesis of this study was that yearlings would have higher levels of oxidative stress in the blood and muscle as measured by malondialdehyde (MDA), total glutathione (GSH-T), glutathione peroxidase (GPx), nitric oxide (NO), cortisol, and creatine kinase (CK) than mares after a single bout of intense exercise; after training, the horses would have similar levels of oxidative stress after a second bout of intense exercise. Ten Standardbred fillies (18 ± 2.4 months) and 10 Standardbred mares (13 ± 2.1 years) ran a repeated sprints exercise test (RSET1) on a treadmill before (RSET1) and after (RSET2) 8 weeks of training. Blood and muscle samples were taken before, during, and after each RSET. Blood samples were analyzed for hematocrit (Hct), total protein (TP), MDA, NO, GPx, GSH-T, cortisol, and CK; muscle samples were analyzed for MDA, NO, GPx, and GSH-T. Analyses were done in the context of a linear mixed model, and data are presented as mean ± SE (P < .05). In RSET1, yearlings had lower TP, Hct, plasma MDA and higher muscle MDA and GSH-T, erythrocyte GSH-T, and higher erythrocyte GPx activity than the mares (P < .05). In RSET2, the trained mares had lower plasma TP and MDA, muscle GSH-T, and higher muscle MDA and NO as compared to RSET1. Trained yearlings had higher muscle NO and erythrocyte GPx in RSET2 as compared to RSET1. Yearlings started with lower oxidative stress and a higher antioxidant status, but after training mares had improved so that few differences were seen between groups in RSET2.

Effects of Age and Exercise Training on Oxidation of Skeletal Muscle and Blood in Mature and Yearling Horses

IntroductionThe objective of this study was to determine if yearlings would have higher oxidative stress and lower antioxidant status than mature mares after a single bout of intense exercise before and after training.MethodsSeven Standardbred yearling fillies (18 ± 2.4 mo) and seven mares (13 ± 2.1 yr) ran a repeated sprints exercise test before (RSET1) and after (RSET2) an 8‐wk training protocol. Blood samples and middle gluteal muscle samples were taken before and after exercise, and throughout recovery. Data is presented as mean ± SE and all analyses were done in the context of a linear mixed model with random intercepts for horse.ResultsIn RSET1, mares had higher plasma malondialdehyde than the yearlings (P&lt;0.05), but the yearlings had higher muscle malondialdehyde, nitric oxide, glutathione and glutathione peroxidase, erythrocyte total glutathione and glutathione peroxidase (P&lt;0.05). In RSET2, yearlings had higher plasma nitric oxide than the mares (P&lt;0.05). In RSET2, the mares had lower plasma malondialdehyde, and higher muscle malondialdehyde, total glutathione and nitric oxide as compared to RSET1 (P&lt;0.05). The yearlings in RSET2 had higher muscle nitric oxide and lower erythrocyte glutathione peroxidase than in RSET1 (P&lt;0.05). Plasma cortisol, creatine kinase and muscle glutathione peroxidase had little difference with age or training.ConclusionsPrior to training, the yearlings had lower lipid peroxidation and higher antioxidants than the mares. Training reduced oxidative stress and improved antioxidant status in the mares, while few effects of training were seen in the yearlings. This suggests that age is an important defense against exercise‐induced oxidative stress.Ethical Animal ResearchRutgers University Institutional Animal Care and Use Review Board approved the study. Sources of funding: none. Competing interests: none.

Comparison of Joint Angles and Muscle Activations between Simulated Stair-climbing Machine and General Ladder

The purpose of this study was to investigate the effects of short-term quercetin (QE) intake on exercise performance, physiological fatigue and emotional responses during the recovery after a single bout of high intensity exercise. Twelve healthy male college students were double blindly and randomly assigned into quercetin (QE) intake trial (2 × 500 mg/day) or placebo-controlled trial (PL). The treatment was given for 7 continuous days, and then subjects performed a single bout of intensive exercise (75% VO2max) until exhaustion. Exercise duration to exhaust and VO2max were recorded before exercise. Other tests, such as heart rate, blood pressure, and profile of mood states (POMS) were conducted and analyzed before exercise and during recovery at 0, 10, 20, 30, and 60 minutes after exercise. However, the changes in lactate concentrations were tested only before exercise, and 0, 30 and 60 minutes after exercise. After completion of the trial, subjects were cross-over and the same protocols were repeated with one-week interval. The results revealed that subjects in QE trial had significantly higher VO2max compared to PL trial. Exercise time to exhaust in QE trial was longer than PE by 11%, but no significant difference. Furthermore, lactate concentration in QE trial was significantly lower than PL trial during 60 minute recovery period. The systolic blood pressure in QE trial was also lower than PL trial. However, QE trial recovered quicker in the change of heart rate than PL trial at 20 minute recovery period. In addition, the scores of fatigue and negative mental factors in POMS for QE trial were also significantly lower than PL trial. This study concluded that QE may enhance the performance of VO2max, delay physical fatigue, and improve negative emotion after an intensive exercise.

Tensiomyographic Characteristics of Rectus Femoris after a Single Bout of Intense Exercise

Problem statement: It is not well known how local fatigue can impair the contractile properties of skeletal muscle, so the aim of this study was to determine the Tensiomyographic (TMG) characteristics of Rectus Femoris (RF) after a single bout of intense exercise. Approach: Twelve healthy male volunteers (mean±SEM; age, 24.16±0.62 years, height 172.02±1.21 cm, body mass 71.84±2.19 kg, BMI 24.42±0.70 kg m-1) were recruited. Results: In session 1, a graded exercise test on cycle ergometer was performed in order to determine subject’s maximal oxygen uptake (VO2max) and power at this key point (pVO2max). In a second testing session, TMG rest values were assessed and then all subjects carried out 2 min of cycling at pVO2max after which TMG analysis was applied again. The results showed subject’s VO2max values of 53.44±2.67 ml kg-1 min-1, reaching a mean pVO2max of 270.83±8.61 W. Maximal radial displacement (Dm) and time from the onset of electrical stimulus to 10% of Dm (Td) were significantly lower at post-test (from 7.577.57±0.92-4.37±0.67 mm; p = 0.01, for Dm and from 25.25±0.57-22.44±0.89 ms; p≤0.05, for Td). Conclusion/Recommendations: It can be concluded that a brief and intense exercise consisting in 2 min of cycling at PVO2max provokes a reduction in contractile properties of RF considering TMG parameters such as Dm and Td. More studies are needed to clarify the role of muscle fatigue on temporal TMG parameters.

The effect of stress-inducible extracellular Hsp72 on human neutrophil chemotaxis: A role during acute intense exercise

We studied the physiological role of the 72 kDa extracellular heat shock protein (Hsp72, a stress-inducible protein) in modulating neutrophil chemotaxis during a single bout of intense exercise performed by sedentary women, together with various cell mechanisms potentially involved in the modulation. For each volunteer, we evaluated neutrophil chemotaxis and serum Hsp72 concentration before and immediately after a single bout of exercise (1 h on a cycle ergometer at 70% VO2 max), and 24 h later. Both parameters were found to be stimulated by the exercise, and had returned to basal values 24 h later. In vitro, there was a dose-dependent increase in chemotaxis when neutrophils were incubated both with physiological Hsp72 concentrations and with a 100 × greater concentration. The chemotaxis was greater when the neutrophils were incubated with the post-exercise Hsp72 concentration than with the basal concentration, suggesting a physiological role for this protein in the context of the stimulation of neutrophil chemotaxis by intense exercise. The 100 × Hsp72 concentration stimulated chemotaxis even more strongly. In addition, Hsp72 was found to have chemoattractant and chemokinetic effects on the neutrophils at physiological concentrations, with these effects being significantly greater with the post-exercise than with the basal Hsp72 concentration. The Hsp72-induced stimulation of neutrophil chemotaxis disappeared when the toll-like receptor 2 (TLR-2) was blocked, and phosphatidylinositol-3-kinase (PI3K), extracellular signal-regulated kinase (ERK), and nuclear transcription factor kappa B (NF-κB) were also found to be involved in the signaling process. No changes were observed, however, in neutrophil intracellular calcium levels in response to Hsp72. In conclusion, physiological concentrations of the stress protein Hsp72 stimulate human neutrophil chemotaxis through TLR-2 with its cofactor CD14, involving ERK, NF-κB, and PI3K, but not iCa2 + , as intracellular messengers. In addition, Hsp72 seems to participate in the stimulation of chemotaxis induced by a single bout of intense exercise performed by sedentary women.

Exercise Induces Apoptosis Of Lymphocytes Subpopulations In Lymphoid Organs

Strenuous exercise affects lymphocyte counts in lymphoid and non-lymphoid organs via different mechanisms like mobilization and redistribution as well as proliferation and apoptosis. The role of apoptosis is currently under focus of research since intensive exercise is well known to increase several apoptosis-inducing factors including glucocorticoids, reactive oxygen species, Fas receptor, TNF-α and intracellular calcium. PURPOSE: To investigate the effects of a single bout of intensive exercise on apoptosis of lymphocyte subpopulations in several lymphoid organs and to study the kinetics of these alterations. METHODS: Eight week old male CD1-mice were assigned to an exercise group or a control group. Mice of the exercise group performed an acute treadmill exercise at 80% VO2max until exhaustion, while controls were exposed to treadmill noise without running. Mice were sacrified either immediately, 3h or 24h after exercise. Thymus, spleen, lung, Peyer's patches, ingiunal lymph nodes and bone marrow were excised and blood samples were taken. Lymphocytes were isolated and stained using PE- conjugated monoclonal antibodies against CD3, CD4 and CD8. Detection of apoptotic cells was performed by flow cytometry using FITC-conjugated annexin V. RESULTS: In spleen an increase of apoptotic CD3+ and CD4+− cells was observed immediately and 24h after exercise. Likewise, apoptosis of CD3+, CD4+ and CD8+− lymphocytes in Peyer's patches and thymus increased immediately after exercise and was still enhanced 24h after exercise. In contrast in bone marrow the increase of apoptotic CD3+, CD4+ and CD8+− cells was delayed. Likewise an increased percentage of apoptotic CD3+ and CD4+− cells in lymph nodes was detected only 24h after exercise. CONCLUSION: An acute bout of intensive treadmill running increased lymphocyte apoptosis in several lymphoid organs, but with different kinetics. We speculate that exercise induced apoptosis in different organs might have a regulatory function to remove activated cells mobilized during exercise. It remains to be shown whether different rates of apoptosis in the lymphoid compartments are related to different concentrations of apoptosis-inducing factors.

Time course of insulin sensitivity and skeletal muscle glycogen synthase activity after a single bout of exercise in horses

The time course of insulin sensitivity, skeletal muscle glycogen and GLUT4 content, and glycogen synthase (GS) activity after a single bout of intense exercise was examined in eight horses. On separate days, a euglycemic-hyperinsulinemic clamp (EHC) was undertaken at 0.5, 4, or 24 h after exercise or after 48 h of rest [control (Con)]. There was no increase in mean glucose infusion rate (GIR) with exercise (0.5-, 4-, and 24-h trials), and GIR was significantly decreased at 0.5 h postexercise (GIR: 8.6 +/- 2.7, 6.7 +/- 2.0, 9.0 +/- 2.0, and 10.6 +/- 2.2 mg.kg(-1).min(-1) for Con and at 0.5, 4, and 24 h, respectively). Before each EHC, muscle glycogen content (mmol glucosyl units/kg dry muscle) was higher (P < 0.05) for Con (565 +/- 102) than for other treatments (317 +/- 84, 362 +/- 79, and 382 +/- 74 for 0.5, 4, and 24 h, respectively) and muscle GLUT4 content was unchanged. Pre-EHC active-to-total GS activity ratio was higher (P < 0.05) at 0.5, 4, and 24 h after exercise than in Con. Post-EHC active GS and GS activity ratio were higher (P < 0.05) in Con and at 24 h. There was a significant inverse correlation (r = -0.43, P = 0.02) between glycogen content and GS activity ratio but no relationship between GS activity and GIR. The lack of increase in insulin sensitivity, determined by EHC, after exercise that resulted in a significant reduction in muscle glycogen content is consistent with the slow rate of muscle glycogen resynthesis observed in equine studies.

The effect of glutamine supplementation on the function of neutrophils from exercised rats

In a recent publication, we showed the protective effect of glutamine on neutrophil apoptosis induced by acute exercise. The purpose of the present study was to examine the effect of a single bout of intensive exercise on rat neutrophil function and the possible effect of glutamine supplementation. An aqueous solution of glutamine was given by gavage (1 g per kg b.w.), 1 h before the exercise session. The exercise was carried out on a treadmill for 1 h at 85% VO2máx.. Neutrophils were obtained by intraperitoneal lavage with PBS. The following parameters were evaluated: phagocytosis capacity, production of nitric oxide and reactive oxygen metabolites, expression of iNOS, and expression of NADPH-oxidase components (p22phox, p47phox and gp91phox). One hour of exercise at 85% VO2max. induced no change in the phagocytosis capacity and reactive oxygen species production but decreased nitric oxide production. When rats received oral glutamine supplementation, the phagocytosis capacity was significantly increased, the decrease in nitric oxide production induced by exercise was abolished and production of reactive oxygen species was raised. Glutamine supplementation presents a significant effect on neutrophil function including changes induced by exercise.

Relations Of Autonomic Cardiac Activity And Individual Performance Capacity?

0440 The heart rate variability (HRV) as a measure of the autonomic cardiac activity is of growing interest in sports medicine performance diagnosis. Whereas long-term endurance training enhances the cardiovascular function, a single bout of intense exercise leads to a progressive decrease of HRV. Recent studies assessed associations of HRV and VO2 and resting heart rate (HR) in athletes. However it remains unclear whether there is a correlation between the aerobic capacity and HRV dynamics following exercise. PURPOSE: To determine the acute effects of a performance test (PT) on HRV in regard to the individual performance capacity. METHODS: 9 healthy male triathletes (age 18–67 y.) were measured before and subsequent to a single PT until exhaustion using short term HRV analyses during a standardised orthostatic tilt-test (supine-standing-supine for 5 min in each case). HRV was quantified by time domain measures (RR-Inter, SDNN, R-MSSD). Spectral power in the low-(LF), high-(HF) and total-(TP) power frequency ranges and the ratio of low- to highfrequency power (LF/HF) was derived using FFT. Wilcoxon tests were performed to determine significant differences of each value post exercise. Using Spearman Rho tests correlations between HRV values and the individual performance capacity (VO2 peak, HR) were assessed. RESULTS: All time domain measures (RR-Inter: 0.9 ± 0.1 vs. 0.7 ± 0.1; SDNN: 5.6 ± 2.9 vs. 2.1 ± 0.9; R-MSSD: 1707.7 ± 1812.3 vs. 54.7 ± 65.5) and frequency domain measures (Tab. 1) decreased significantly (p < .05) after PT. No significant correlations were found for HRV and VO2peak and HR.Tab. 1: Mean ± standard deviation for frequency domain indices [ms2] pre- and post PTCONCLUSION: The results demonstrate a decreased autonomic cardiac activity and impaired sympathovagal balance on account of the high exertion in the course of a PT. The nonsignificant correlations between HRV and VO2 peak and HR suggest the implementation of HRV measures as an additional parameter of the individual performance capacity in terms of a multidimensional sports medicine performance diagnosis.

Relations Of Autonomic Cardiac Activity And Individual Performance Capacity?

0440 The heart rate variability (HRV) as a measure of the autonomic cardiac activity is of growing interest in sports medicine performance diagnosis. Whereas long-term endurance training enhances the cardiovascular function, a single bout of intense exercise leads to a progressive decrease of HRV. Recent studies assessed associations of HRV and VO2 and resting heart rate (HR) in athletes. However it remains unclear whether there is a correlation between the aerobic capacity and HRV dynamics following exercise. PURPOSE: To determine the acute effects of a performance test (PT) on HRV in regard to the individual performance capacity. METHODS: 9 healthy male triathletes (age 18–67 y.) were measured before and subsequent to a single PT until exhaustion using short term HRV analyses during a standardised orthostatic tilt-test (supine-standing-supine for 5 min in each case). HRV was quantified by time domain measures (RR-Inter, SDNN, R-MSSD). Spectral power in the low-(LF), high-(HF) and total-(TP) power frequency ranges and the ratio of low- to highfrequency power (LF/HF) was derived using FFT. Wilcoxon tests were performed to determine significant differences of each value post exercise. Using Spearman Rho tests correlations between HRV values and the individual performance capacity (VO2 peak, HR) were assessed. RESULTS: All time domain measures (RR-Inter: 0.9 ± 0.1 vs. 0.7 ± 0.1; SDNN: 5.6 ± 2.9 vs. 2.1 ± 0.9; R-MSSD: 1707.7 ± 1812.3 vs. 54.7 ± 65.5) and frequency domain measures (Tab. 1) decreased significantly (p < .05) after PT. No significant correlations were found for HRV and VO2peak and HR.Tab. 1: Mean ± standard deviation for frequency domain indices [ms2] pre- and post PTCONCLUSION: The results demonstrate a decreased autonomic cardiac activity and impaired sympathovagal balance on account of the high exertion in the course of a PT. The nonsignificant correlations between HRV and VO2 peak and HR suggest the implementation of HRV measures as an additional parameter of the individual performance capacity in terms of a multidimensional sports medicine performance diagnosis.

METABOLIC AND MITOGENIC SIGNAL TRANSDUCTION IN RESPONSE TO INTENSE EXERCISE IN ENDURANCE-TRAINED HUMANS

We determined the extent to which mitogen-activated protein kinase (MAPK) and 5'-AMP-activated protein kinase (AMPK) signaling cascades are activated in response to intense exercise in skeletal muscle from highly-trained athletes who performed 8 times; 5 min workbouts at 86 ± 1% of VO2max with 60 s recovery. Muscle biopsies were taken from the v. lateralis before and immediately after the training session. Extracellular regulated kinase (ERK1/2) and p38 MAPK phosphorylation were determined by immunoblot analysis using phosphospecific antibodies. Activation of mitogen and stress-activated kinase 1 (MSK1; a downstream target of ERK1/2 and p38 MAPK) and α1 and α2 subunits of AMPK (components of a stress-responsive protein kinase cascade) were determined by immune complex assays. Muscle [glycogen] was reduce 51% (P < 0.01), whereas muscle [lactate] was increased 533% (P < 0.01) after exercise. Phosphorylation of ERK1/2 and p38 MAPK and activity of the downstream kinase MSK1 were increased 120% (P < 0.05), 160% (P = 0.09) and 150% (P < 0.05), respectively after exercise. Phosphorylation of histone H 3, a substrate of MSK1, was increased 200% (P < 0.001), whereas the phosphorylation of the transcription factor CREB was repressed (80-fold lower) in response to exercise (P < 0.0001). An isoform-specific exercise-induced activation of AMPK was observed: AMPKα1 activity was not altered, whereas, AMPKα2 activity was increased 226% (P < 0.05). Exercise-induced AMPKα2 activity was correlated with changes in muscle lactate concentration (r = 0.74, P < 0.05). In conclusion, a single bout of intense exercise in already highly-trained humans leads to profound activation of MAPK signaling casades, including downstream targets MSK1 and histone H 3. Activation of these downstream targets provides a potential mechanism by which exercise induces gene transcription. Furthermore, exercise elicits an isoform-specific induction of AMPK signaling in skeletal muscle that was correlated with metabolic stress. Thus, AMPKα2 may be involved in exercise responses on both metabolism and gene expression in skeletal muscle.

Energy system interaction and relative contribution during maximal exercise.

There are 3 distinct yet closely integrated processes that operate together to satisfy the energy requirements of muscle. The anaerobic energy system is divided into alactic and lactic components, referring to the processes involved in the splitting of the stored phosphagens, ATP and phosphocreatine (PCr), and the nonaerobic breakdown of carbohydrate to lactic acid through glycolysis. The aerobic energy system refers to the combustion of carbohydrates and fats in the presence of oxygen. The anaerobic pathways are capable of regenerating ATP at high rates yet are limited by the amount of energy that can be released in a single bout of intense exercise. In contrast, the aerobic system has an enormous capacity yet is somewhat hampered in its ability to delivery energy quickly. The focus of this review is on the interaction and relative contribution of the energy systems during single bouts of maximal exercise. A particular emphasis has been placed on the role of the aerobic energy system during high intensity exercise. Attempts to depict the interaction and relative contribution of the energy systems during maximal exercise first appeared in the 1960s and 1970s. While insightful at the time, these representations were based on calculations of anaerobic energy release that now appear questionable. Given repeated reproduction over the years, these early attempts have lead to 2 common misconceptions in the exercise science and coaching professions. First, that the energy systems respond to the demands of intense exercise in an almost sequential manner, and secondly, that the aerobic system responds slowly to these energy demands, thereby playing little role in determining performance over short durations. More recent research suggests that energy is derived from each of the energy-producing pathways during almost all exercise activities. The duration of maximal exercise at which equal contributions are derived from the anaerobic and aerobic energy systems appears to occur between 1 to 2 minutes and most probably around 75 seconds, a time that is considerably earlier than has traditionally been suggested.

The Effects of Intense Physical Exercise on Secondary Antibody Response in Young and Old Mice

Based largely on data from young subjects, intense physical exercise is believed to suppress immune function. In addition, immune function, including secondary antibody response, declines with advancing age. Therefore, intense exercise in old subjects may further suppress the secondary antibody response. The purpose of this in vivo study was to investigate the effects of intense physical exercise on secondary antibody response in young (6-8 weeks) and old (22-24 months) C57BL/6 mice. Data were obtained from 22 young and 18 old C57BL/6 mice that were immunized to human serum albumin (HSA) and randomly divided into 3 groups. Two groups were exposed to a single bout of intense exercise to exhaustion and immediately boosted with an injection of HSA. The first group did not exercise further, but the second group continued with daily bouts of intense exercise to exhaustion for 9 days. The third group (control group) did not undergo intense exercise, but received the booster injection of HSA at the same time as the other groups. Ten days after the HSA booster injection, when high level of antibodies are produced in secondary antibody response, serum anti-HSA antibodies were measured by enzyme-linked immunosorbent assay. Young mice did not show suppression of secondary antibody response following intense exercise. However, old mice, exposed to a single bout of intense exercise, had an enhanced response similar to the response seen in young control mice. The widely accepted hypothesis of immunosuppression resulting from intense exercise may not be true for old mice.

Acute and Subacute Changes in the Ultrasound Measurements of the Calcaneus Following Intense Exercise

The amount of exercise necessary to cause bone structural change in humans is unknown. We examined whether a single bout of intense exercise in vivo leads to acute and subacute changes in the physical properties of bone as measured by ultrasound. It was hypothesized that structural changes such as accumulation of fatigue microdamage would result in a decrease in velocity of sound (VOS) and broadband ultrasound attenuation (BUA) across the calcaneus. We performed a prospective cohort study in 111 (97 M, 14 F) entrants of the 1996 Melbourne marathon (42.3 km) and 28 (10 M, 18 F) nonrunning controls. Runners had a mean (SD) age of 45.3 +/- 11.4 years (range 20-75), had completed 15.2 +/- 17.3 prior marathons (0-88), and had been running regularly for 14.2 +/- 9.2 years (0.25-50). An ultrasound densitometer (Cuba Clinical, McCue) was used to measure VOS and BUA across the right calcaneus. Runners were tested on three occasions: 1-3 days prior to, immediately after (<2 hours), and 5-6 days following the marathon. Seventy-three (66%) runners presented for all three measurements. Controls were tested on three occasions with the same time intervals as the runners. BUA values in the runners were significantly elevated by 5.0% immediately after the marathon but returned to baseline levels by the third test session (P = 0. 0001). Changes in BUA values in the controls were not significant and all were less than 0.7% (P = 0.88). Age was a significant independent predictor of the BUA change between test 1 and test 2 in the runners (beta = 0.2094; SE = 0.0917; P = 0.03). VOS measurements were not significantly different across the three testing sessions in both the runners (P = 0.07) and the controls (P = 0.33). Therefore, ultrasound measurements of BUA and VOS did not detect evidence of lasting structural change in the calcaneus following a marathon.

Mechanism of exercise-induced augmentation of lymphokine activated killer (LAK) cell activity in the horse.

Intense exercise affects various parameters of the immune system. The overall effect of exercise on immune function is dependent upon the physical condition of the subject, the intensity and duration of the exercise period, and the immune parameter assessed. Unconditioned horses subjected to a single bout of intensive exercise exhibit multiple alterations in immune function, including an augmentation of lymphokine activated killer (LAK) cell function. This increase in LAK cell activity is not due to an increase in circulating LAK precursors. While peripheral blood mononuclear cells from exercising horses exhibit greater responsiveness to IL-2, this is not due to an increase in IL-2 receptor expression. LAK cell generation in vitro is augmented by those catecholamines and neuropeptides which are produced during exercise, suggesting a direct effect of these compounds on LAK cell generation at a step post IL-2 receptor binding.

Effect of exercise on lipolytic sensitivity in endurance-trained athletes.

Studies performed in vitro suggest that an acute bout of exercise increases the lipolytic response to beta-adrenergic stimulation. We evaluated the effect of exercise on lipolytic sensitivity in vivo in five endurance-trained athletes. The rate of appearance (Ra) of glycerol in plasma, an index of whole body lipolysis, was determined during 60 min of epinephrine infusion (0.015 microgram.kg-1.min-1) on two occasions: 1) at basal resting conditions and 2) 90 min after completing 1 h of high-intensity (70% O2 uptake) cycle ergometer exercise. Total glycerol Ra during epinephrine infusion in the basal state (352 +/- 35 mumol.kg-1. 60 min-1) was not significantly different from the value obtained after high-intensity exercise (439 +/- 58 mumol.kg-1. 60 min-1). However, the increase in glycerol Ra above baseline during epinephrine infusion was lower after (30 +/- 16 mumol.kg-1. 60 min-1) than before (148 +/- 28 mumol.kg-1. 60 min-1) exercise because of the high postexercise baseline value (P < 0.05). Mean plasma free fatty acid (FFA) concentration was lower during exercise than during epinephrine infusion despite a greater rate of lipolysis during exercise. The slope of change in plasma FFA with respect to glycerol RA was lower during exercise (0.0171 +/- 0.006) than during epinephrine infusion (0.0835 +/- 0.018) (P < 0.05). We conclude that a single bout of intense exercise does not increase in vivo lipolytic sensitivity to beta-adrenergic stimulation in endurance-trained athletes. In addition, plasma FFA concentration represents the balance between plasma FFA inflow and tissue uptake and cannot be used as an index of lipolytic activity during certain physiological conditions, such as exercise.