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Biomedical subjects

J Mark Davis

Publications and source records attributed to J Mark Davis.

At least 19 recordsLinked to original sources
PubMed2006

Circadian variation in swim performance.

Previous findings of time-of-day differences in athletic performance could be confounded by diurnal fluctuations in environmental and behavioral "masking" factors (e.g., sleep, ambient temperature, and energy intake). The purpose of this study was to examine whether there is a circadian rhythm in swim performance that is independent of these masking factors. Experienced swimmers (n = 25) were assessed for 50-55 consecutive hours in the laboratory. The swimmers followed a 3-h "ultra-short" sleep-wake cycle, involving 1 h of sleep in darkness and 2 h of wakefulness in dim light, that was repeated throughout the observation. The protocol distributes behavioral and environmental masking factors equally across the 24-h period. Each swimmer was scheduled to perform six maximal-effort 200-m swim trials that were distributed equally across eight times of day (n = 147 trials). Each trial was separated by 9 h. A cosine fit of intra-aural temperature data established the time of the lowest body temperature (Tmin). Swim performances were z-transformed and compared across the eight times of day and across twelve 2-h intervals relative to Tmin. Analysis of covariance, controlling for trial number, revealed a significant (P < 0.001) pattern in swim performance relative to environmental and circadian times of day. Performance peaked 5-7 h before Tmin (approximately 2300) and was worst from 1 h before to 1 h after Tmin (approximately 0500). Mean swim performance was 169.5 s; circadian variation from peak to worst performance was 5.8 s. These data suggest a circadian rhythm in athletic performance independent of environmental and behavioral masking effects.

Adult↗
PubMed2006

Modulation of overload-induced inflammation by aging and anabolic steroid administration.

Aging can alter the skeletal muscle growth response induced by overload. The initiation of overload induces muscle extracellular matrix expansion, increased cellularity, and inflammatory gene expression, which are all related to processes important for myofiber growth. These remodeling processes are also biological targets of testosterone. It is not certain how aging affects the inflammatory response to functional overload and whether anabolic steroid administration can alter this response. The effect of anabolic steroid administration on inflammatory processes during functional overload is not known. The purpose of this study was to determine if age altered the skeletal muscle inflammatory response at the onset of functional overload and whether anabolic steroid administration would modulate this response in young or older animals. Five-month and 25 month F344 x BRN rats were given nandrolone decanoate (ND) (6 mg/kg bw/wk) or sham injections for 3 weeks, and then the soleus muscle was overloaded (OV) for 3 days by synergist ablation. ND alone induced a 230% increase in ED1(+) cells in 5 month muscle. Three days of OV had no effect on ED1(+) cell number at either age. OV combined with ND induced a 90% increase in ED2(+) cells in 5 month muscle, while there was no effect of either treatment alone at this age. In 25 month muscle, OV induced a 40% increase in ED2(+) cells. Regardless of age, OV induced muscle TNF-alpha mRNA expression (300%) and IL-6 mRNA expression (900%). ND attenuated OV-induced IL-6 mRNA but not TNF-alpha expression in both age groups. The overload induction of IL-1beta mRNA was 3-fold greater in 25 month muscle (1400%), compared to 5 month muscle (400%). ND administration ablated the overload IL-1beta mRNA induction in 25 month muscle. Anabolic steroid administration can suppress inflammatory cytokine gene expression at the onset of overload and this effect is age dependent.

Aging↗
PubMed2006

Role of brain IL-1beta on fatigue after exercise-induced muscle damage.

Brain cytokines, induced by various inflammatory challenges, have been linked to sickness behaviors, including fatigue. However, the relationship between brain cytokines and fatigue after exercise is not well understood. Delayed recovery of running performance after muscle-damaging downhill running is associated with increased brain IL-1beta concentration compared with uphill running. However, there has been no systematic evaluation of the direct effect of brain IL-1beta on running performance after exercise-induced muscle damage. This study examined the specific role of brain IL-1beta on running performance (either treadmill or wheel running) after uphill and downhill running by manipulating brain IL-1beta activity via intracerebroventricular injection of either IL-1 receptor antagonist (ra; downhill runners) or IL-1beta (uphill runners). Male C57BL/6 mice were assigned to the following groups: uphill-saline, uphill-IL-1beta, downhill-saline, or downhill-IL-1ra. Mice initially ran on a motor-driven treadmill at 22 m/min and -14% or +14% grade for 150 min. After the run, at 8 h (wheel cage) or 22 h (treadmill), uphill mice received intracerebroventricular injections of IL-1beta (900 pg in 2 microl saline) or saline (2 microl), whereas downhill runners received IL-1ra (1.8 microg in 2 microl saline) or saline (2 microl). Later (2 h), running performance was measured (wheel running activity and treadmill run to fatigue). Injection of IL-1beta significantly decreased wheel running activity in uphill runners (P<0.01), whereas IL-1ra improved wheel running in downhill runners (P<0.05). Similarly, IL-1beta decreased and Il-1ra increased run time to fatigue in the uphill and downhill runners, respectively (P<0.01). These results support the hypothesis that increased brain IL-1beta plays an important role in fatigue after muscle-damaging exercise.

Animals↗
PubMed2006

Ibuprofen use, endotoxemia, inflammation, and plasma cytokines during ultramarathon competition.

The primary purpose of this study was to measure the influence of ibuprofen use during the 160-km Western States Endurance Run on endotoxemia, inflammation, and plasma cytokines. Subjects included 29 ultramarathoners who consumed 600 and 1200 mg ibuprofen the day before and on race day, respectively, and 25 controls that competed in the race but avoided ibuprofen and all other medications. Blood and urine samples were collected the morning prior to and immediately following the race, and subjects recorded muscle soreness during the week following the race using a 10-point Likert scale (DOMS). Race time (25.8+/-.6 and 25.6+/-.8 h, respectively) and ratings of perceived exertion (RPE, 6-20 scale) (14.6+/-.4 and 14.5+/-.2, respectively) did not differ significantly between ibuprofen users and nonusers. Ibuprofen use compared to nonuse was linked to a smaller increase in urine creatinine (P=.038), higher plasma levels of lipopolysaccharide (group effect, P=.042), and greater increases (pre-to-post race) in serum C-reactive protein and plasma cytokine levels for interleukin (IL)-6, IL-10, IL-8, IL-1 ra, granulocyte colony-stimulating factor, monocyte chemotactic protein 1, and macrophage inflammatory protein 1 beta, but not tumor necrosis factor alpha. Post-race DOMS and serum creatine kinase levels did not differ significantly between ibuprofen users and nonusers (20,621+/-3565 and 13,886+/-3068 microcal/L, respectively, P=.163). In conclusion, ibuprofen use compared to nonuse by athletes competing in a 160-km race did not alter muscle damage or soreness, and was related to elevated indicators of endotoxemia and inflammation.

Adult↗
PubMed2006

Trail making test errors and executive function in schizophrenia and depression.

The Trail Making Test (TMT) frequently is used as a measure of executive cognitive function. However, traditional use of test completion time as the primary outcome score does not give the more detailed information on cognitive processes that analysis of test-taking errors may provide. The present study compared TMT performance of three groups: patients with schizophrenia, patients with major depression, and healthy control participants (n = 30 for each group). Three operationally defined error types were examined: (a) tracking, (b) perseverative, and (c) proximity. Although both patient groups were slower than the healthy control group, only the schizophrenia group made significantly more errors, particularly tracking errors, suggesting a greater degree of cognitive disorganization. Within-group analysis of a larger group of schizophrenia patients (n = 84) revealed that TMT time was most strongly associated with the Withdrawal-Retardation factor of the Brief Psychiatric Rating scale. In contrast, TMT errors were most strongly associated with the Conceptual Disorganization factor. Comparisons of TMT scores and other cognitive tests showed moderate to high associations with tests of working memory, psychomotor speed, and executive function. Stepwise regression analysis revealed an independent association between Digit Cancellation and Part B Time, indicating a unique contribution of visuomotor scanning to performance. In contrast, Part B errors were uniquely associated with the Verbal Series Attention Test and the Token Test, tests of mental tracking and executive-mediated working memory, respectively. These findings demonstrate the utility of TMT error analysis in revealing cognitive deficits not traditionally captured using completion time as the sole outcome variable.

Adult↗
PubMed2006

Blood leukocyte mRNA expression for IL-10, IL-1Ra, and IL-8, but not IL-6, increases after exercise.

The primary purpose of this project was to study exercise-induced leukocyte cytokine mRNA expression. Changes in plasma cytokine levels and blood leukocyte mRNA expression for interleukin-6 (IL-6), IL-8, IL- 10, and IL-1 receptor antagonist (IL-1Ra) were measured in 12 athletes following 2 h of intensive cycling ( approximately 64% Watts(max)) while ingesting a carbohydrate or placebo beverage (randomized and double blinded). Blood samples were collected 30 min preexercise and immediately and 1 h postexercise. Carbohydate compared with placebo ingestion attenuated exercise-induced changes in plasma cortisol (8.8% vs. 62%, respectively), epinephrine (-9.2% vs. 138%), IL-6 (10-fold vs. 40-fold), IL-10 (8.9-fold vs. 26-fold, and IL-1Ra (2.1-fold vs. 5.6-fold). Significant time effects were measured for blood leukocyte IL-8 (2.4-fold increase 1 h postexercise), IL-10 (2.7-fold increase), IL-1Ra (2.2-fold increase), and IL-6 (0.8-fold decrease) mRNA content, with no significant differences between Cho and Pla test conditions. In summary, gene expression for IL-8, IL-10, and IL-1Ra, but not IL-6, is increased in blood leukocytes taken from athletes following 2 h of intensive cycling and is not influenced by carbohydrate compared with placebo ingestion. mRNA expression was high enough to indicate a substantial contribution of blood leukocytes to plasma levels of IL-8, IL-10, and IL-1Ra during prolonged exercise.

Adult↗
PubMed2006

Gender differences in macrophage antiviral function following exercise stress.

INTRODUCTION: In male mice, exhaustive exercise increases susceptibility to respiratory infection following intranasal inoculation with herpes simplex virus-1 (HSV-1), whereas moderate exercise decreases the risk of infection. These responses have been linked with altered macrophage antiviral resistance, among other immune mechanisms. Female mice appear to be better protected from death than male mice following HSV-1 infection, although their response to exercise stress is similar. The possible immune mechanisms, however, have not been explored. PURPOSE: This study was conducted to examine gender differences in macrophage antiviral resistance following repeated moderate and exhaustive treadmill exercise. METHODS: Male (M, N = 36) and female (F, N = 36) CD-1 mice were randomly assigned to moderate exercise (Mod), exhaustive exercise (Exh), or control (C) groups. Exercise was done daily for 3 d; moderate exercise consisted of treadmill running for 90 min, whereas exhaustive exercise consisted of running to volitional fatigue (approximately 50 min). RESULTS: Females had greater macrophage antiviral resistance to HSV-1 than males in C and Mod (P < 0.05), but not Exh; Mod increased resistance, whereas Exh decreased resistance similarly in both genders (P < 0.001). CONCLUSIONS: These data suggest that altered macrophage antiviral resistance to HSV-1 may contribute to gender differences in in vivo resistance to HSV-1 respiratory infection at rest, as well as following moderate and exhaustive exercise.

Animals↗
PubMed2005

Recovery of running performance following muscle-damaging exercise: relationship to brain IL-1beta.

Recovery following muscle-damaging downhill running is associated with increased muscle inflammatory cytokines. Various inflammatory challenges can also increase cytokines in the brain, which have been linked to sickness behaviors, including fatigue, but little is known about the brain cytokine response to stressful exercise. We used a downhill running model to determine the relationship between brain IL-1beta and recovery of running performance. Male C57BL/6 mice were assigned to: downhill (DH), uphill (UH), or non-running control (Con) groups and run on a treadmill at 22 m/min and -14% or 14% grade, for 150 min. Following the run, a subset of DH and UH was placed into activity wheel cages where voluntary running activity was measured for 7 days. A second subset was run to fatigue on a motorized treadmill at 36 m/min, 8% grade at 24, 48, and 96 h post-up/downhill run. A third subset of DH, UH, and Con mice had brains dissected and assayed for IL-1beta at 24 and 48 h. DH resulted in delayed recovery of both voluntary wheel-running and treadmill running to fatigue as compared to UH (p < .05). DH was also associated with increased IL-1beta concentrations in cortex (at 24 and 48 h) and cerebellum (24 h) as compared to UH and Con. UH was not different than Con in any brain region. Eccentric-biased downhill running results in an increase in plasma CK and delayed recovery in running performance, as compared to the more metabolically demanding uphill running, and this was associated with increased concentrations of IL-1beta in regions of the brain responsible for movement, coordination, motivation, perception of effort, and pain.

Animals↗
PubMed2005

Myofiber degeneration/regeneration is induced in the cachectic ApcMin/+ mouse.

Cachexia is characterized as an inflammatory state induced by the cancer environment, which is accompanied by the loss of muscle and fat mass. Well-investigated mechanisms of cachexia include the suppression of myofiber protein synthesis and the induction of the protein degradation. However, it is not well characterized whether chronic inflammation during cachexia induces myofiber degeneration, which contributes to muscle mass loss and decreased functional capacity. The purpose of this study was to determine whether Apc(Min/+) mice, which demonstrate a chronic systemic inflammatory state due to an intestinal tumor burden, undergo cachexia and whether the myofibers exhibit signs of degeneration and/or regeneration. Six-month-old female Apc(Min/+) body weight decreased 21% compared with C57BL/6 mice and was not the result of blunted growth. Apc(Min/+) gastrocnemius muscle was reduced 45%, and soleus mean fiber cross-sectional area decreased 24% vs. C57BL/6 mice. Soleus muscle morphology demonstrated pathology of myofibers undergoing degeneration and/or regeneration. These data demonstrate that the Apc(Min/+) mouse becomes cachectic by 6 mo of age and that skeletal muscle degeneration and regeneration may be related to the muscle loss.

Adenomatous Polyposis Coli↗
PubMed2005

Decreased intestinal polyp multiplicity is related to exercise mode and gender in ApcMin/+ mice.

Moderate-intensity treadmill running can alter male Apc(Min/+) mouse polyp formation. This purpose of this study was to examine whether exercise mode differentially affects Apc(Min/+) mouse intestinal polyp development in male and female mice. Male and female Apc(Min/+) mice were randomly assigned to control, treadmill (18 m/min; 60 min/day; 6 days/wk), or voluntary wheel running (24-h access) groups. Nine weeks of training decreased total intestinal polyps by 29% in male treadmill runners (66 +/- 9; P = 0.038) compared with male controls (93 +/- 7). The number of large polyps (>/=1-mm diameter) were also reduced by 38% in male treadmill runners (49 +/- 6; P = 0.005) compared with male controls (79 +/- 6). Treadmill running in female Apc(Min/+) mice and wheel running in both genders did not affect polyp number or size. Spleen weight decreased in male treadmill runners (91 +/- 9 mg; P = 0.011) and wheel runners (75 +/- 6 mg; P = 0.004) compared with controls (141 +/- 13 mg). Plasma IL-6 was reduced by 96% in male treadmill runners (1.2 +/- 0.6 pg/ml) and 78% in male wheel runners (6.6 +/- 3.3 pg/ml) compared with control mice (27.9 +/- 2.8 pg/ml; P < 0.05). Female mice responded similarly with an 86% decrease in plasma IL-6 with treadmill running (3.2 +/- 1.2 pg/ml) and 90% decrease with wheel running (2.9 +/- 2.0 pg/ml) compared with control mice (21.1 +/- 5.3 pg/ml; P < 0.05). The crypt depth-to-villus height ratio in the intestine, an indirect marker of intestinal inflammation, decreased by 21 (P = 0.024) and 24% (P = 0.029), respectively, in male and female treadmill runners but not wheel runners. Physical activity-induced attenuation of intestinal polyp number and size is dependent on exercise mode and differs between genders. The modulation of systemic and intestinal inflammation may also depend on exercise mode.

Adenomatous Polyposis Coli Protein↗
PubMed2005

Carbohydrate feedings during team sport exercise preserve physical and CNS function.

PURPOSE: This study was designed to examine the effect of carbohydrate (CHO) feedings on physical and central nervous system (CNS) function during intermittent high-intensity exercise with physical demands similar to those of team sports such as basketball. METHODS: Twenty active men (N = 10) and women (N = 10), with experience competing in team sports, performed three practice sessions before two experimental trials during which they were fed either a 6% CHO solution or a flavored placebo (PBO). Experimental trials consisted of four 15-min quarters of shuttle running with variable intensities ranging from walking (30% VO(2max)), to running (120% VO(2max)), to maximal sprinting, and 40 jumps at a target hanging at 80% of their maximum vertical jump height. Subjects received 5 mL.kg(-1) of fluid before exercise and 3 mL.kg(-1) after exercise, in addition to 3 mL.kg(-1) over a 5-min span after the first and third quarters, and 8 mL.kg(-1) during a 20-min halftime. During each break, the subjects performed a battery of tests measuring peripheral and CNS function, including 20-m sprints, a 60-s maximal jumping test, internal and external mood evaluation, cognitive function, force sensation, tests of motor skills, and target-jumping accuracy. RESULTS: Compared with PBO, CHO feedings during exercise resulted in faster 20-m sprint times and higher average jump height in the fourth quarter (P < 0.05). CHO feedings also reduced force sensation, enhanced motor skills, and improved mood late in exercise versus PBO (P < 0.05). CONCLUSION: These results suggest that CHO feedings during intermittent high-intensity exercise similar to that of team sports benefited both peripheral and CNS function late in exercise compared with a flavored placebo.

Adult↗
PubMed2005

Muscle cytokine mRNA changes after 2.5 h of cycling: influence of carbohydrate.

PURPOSE: To study the effect of carbohydrate compared to placebo ingestion on plasma cytokines and muscle cytokine mRNA following 2.5 h of intensive cycling in 15 trained cyclists. METHODS: Fifteen trained cyclists cycled for 2.5 h at 60% Wmax on two occasions while receiving 4 mL.kg.15 min carbohydrate (6%) (CHO) or placebo (PLA) beverages in a randomized, counterbalanced design. Blood and vastus lateralis muscle biopsy samples were collected before and after exercise and 12 h postexercise and compared to samples taken from five cyclists who rested in the lab during the exercise sessions. Blood cell counts were determined, and plasma was analyzed for interleukin (IL)-6, IL-10, IL-1 receptor antagonist (ra), IL-8, cortisol, epinephrine, glucose, and insulin. Muscle was analyzed for glycogen content and relative gene expression of four cytokines, IL-6, IL-8, tumor necrosis factor (TNF) alpha, and IL-1beta, using real-time quantitative reverse transcriptase polymerase chain reaction. RESULTS: Plasma glucose and insulin were higher, and epinephrine, cortisol, IL-6, IL-10, and IL-1ra, but not IL-8, were significantly lower postexercise in CHO versus PLA. Muscle glycogen content decreased 68% immediately postexercise and the pattern of change did not differ between CHO and PLA. Muscle IL-6, IL-8, TNF-alpha, but not IL-1beta mRNA increased immediately postexercise compared to controls, with no differences between CHO and PLA. CONCLUSION: CHO compared to PLA beverage ingestion attenuated the increase in plasma cortisol, epinephrine, IL-6, IL-10, and IL-1ra, but not muscle IL-6, IL-8, and TNF-alpha mRNA in athletes cycling 2.5 h at 60% Wmax.

Bicycling↗
PubMed2004

Cumulative effects of intermittent maximal contractions on voluntary activation deficits.

The purpose of this research was to provide more definitive support for the hypothesis that prolonged muscle activation at high intensities increases voluntary activation deficits. Interpolated twitch responses were evoked during maximal and sub-maximal voluntary contractions of the soleus muscle in 10 college-aged students. Maximal voluntary contractions (MVC), maximal muscle twitches, and interpolated twitch responses were measured before, during, and after fatiguing isometric exercise, five bouts of 20 intermittent MVCs. The relationship between voluntary activation and force was studied by evoking interpolated twitches during sub-maximal voluntary contractions on Day 1 and pre-post fatigue on Day 2. Intraclass reliability coefficients for the MVC, maximal muscle twitch, and interpolated twitch responses were adequate across trials and days (R > or = .80). MVC force and maximal twitch force decreased after the fatiguing exercise bouts by 28% and 32%, respectively (p < .05). Voluntary activation of the fatigue-resistant soleus muscle decreased by 10% after the first five min of maximal exercise with a subsequent decrease of 9% occurring after 25 min of maximal exercise (p < .05). At the end of the experimental session, approximately 30 min after the end of the fatiguing exercise, decreases in 100% MVC force, maximal muscle twitch force, and voluntary activation were still evident: 22%, 23%, and 11%, respectively (p < .05). Post-fatigue, there were also changes in neural strategies for voluntary activation of the soleus muscle at the higher sub-maximal efforts, > or = 70% MVC target levels (p < .05). These data demonstrate the cumulative effects of prolonged exercise on voluntary activation.

Adult↗
PubMed2004

Effects of oat beta-glucan on innate immunity and infection after exercise stress.

PURPOSE: To test the effects of oat beta-glucan (ObetaG) on respiratory infection, macrophage antiviral resistance, and NK cytotoxicity. METHODS: Mice were randomly assigned to one of four groups: Ex-H2O, Ex-ObetaG, Con-H2O, or Con-ObetaG. ObetaG was fed in the drinking water for 10 d before intranasal inoculation of HSV-1 or sacrifice. Exercise consisted of treadmill running to volitional fatigue (approximately 140 min) for three consecutive days. Fifteen minutes after the last bout of exercise or rest, mice (N = 24) were intranasally inoculated with a standardized dose of HSV-1. Mice were monitored twice daily for morbidity and mortality. Additional mice were sacrificed after exercise, peritoneal macrophages were obtained via i.p. lavage and assayed for antiviral resistance to HSV-1 (N = 18), and spleens were harvested and assayed for NK cell cytotoxicity (N = 12). RESULTS: Exercise stress was associated with a 28% increase in morbidity (P = 0.036) and 18% increase in mortality (P = 0.15). Ingestion of ObetaG before infection prevented this increase in morbidity (P = 0.048) and mortality (P = 0.05). Exercise stress was associated with a decrease in macrophage antiviral resistance (P = 0.007), which was blocked by ingestion of ObetaG (P < 0.001). There were no effects of exercise or ObetaG on NK cytotoxicity. CONCLUSION: These data suggest that daily ingestion of ObetaG may offset the increased risk of URTI associated with exercise stress, which may be mediated, at least in part, by an increase in macrophage antiviral resistance.

Animals↗
PubMed2004

Gender differences in viral infection after repeated exercise stress.

UNLABELLED: Fatiguing exercise can increase susceptibility to respiratory infection after intranasal inoculation with herpes simplex virus-1 (HSV-1) in male mice. Although gender differences in susceptibility to certain pathogens do exist, it is unknown whether female mice will respond differently than males in response to strenuous exercise and HSV-1 infection. PURPOSE: To test the effects of gender on susceptibility to HSV-1 respiratory infection after repeated exhaustive exercise. METHODS: Male (N = 86) and female (N = 89) CD-1 mice (approximately 60 d old) were randomly assigned to exercise (Ex) or control (C) groups. Exercise consisted of 3 d of treadmill running at 36 m x min(-1) at 8% grade until volitional fatigue (135 +/- 5min). Fifteen minutes after the last bout of exercise, Ex and C mice were inoculated intranasally with a standard dose (LD30) of HSV-1. Mice were monitored for 21 d for morbidity (time to sickness and symptom severity) and mortality. RESULTS: Run time to fatigue was significantly longer in females than males (P = 0.027). Significant gender differences in susceptibility to infection were found after exercise stress. In males, exercise stress resulted in increased morbidity (66%, P < 0.05) and mortality (30%, P < 0.05) whereas in females, exercise stress only resulted in increased morbidity (66%, P < 0.05). CONCLUSION: Results suggest that although males and females have similar morbidity rates after infection and exercise stress, females recover to a greater extent and are ultimately better protected from death.

Animals↗
PubMed2003

Effects of short-term exercise training on plasminogen activator inhibitor (PAI-1).

PURPOSE: To observe the effects of exercise training on plasminogen activator inhibitor, type-1 (PAI-1), tissue plasminogen activator (tPA), and associated metabolic variables in sedentary men and women. METHODS: A randomized, controlled experimental design was used to examine the influence of 10 d of moderate-intensity exercise training on measures of fibrinolysis. Sixteen men and 16 women between the ages of 50 and 70 yr were randomly assigned to exercise (EX) and control groups (CON) that were balanced for gender and hormone replacement therapy. Blood samples were collected on days 1, 2, 11, and 12 for measurement of plasma PAI-1, tPA, insulin, glucose, and triglyceride. Subjects in EX performed 50 min of treadmill walking at an intensity corresponding to 65% of heart rate reserve each day for 10 consecutive days. RESULTS: There were no significant changes in PAI-1, tPA, or associated metabolic variables between EX and CON during the intervention period. Within EX subjects, those with higher body fatness had a significant decrease in insulin and triglyceride compared with those with lower body fatness. However, no changes in fibrinolytic measures were observed within these subgroups. CONCLUSIONS: Short-term exercise training does not change PAI-1 levels in normal, asymptomatic men and women. In addition, modest decreases in insulin and triglyceride in individuals with elevated body fatness do not result in changes in PAI-1 after short-term training. It appears likely that decreases in PAI-1 with exercise training require decreases in adiposity and/or marked changes in metabolic variables.

Aged↗
PubMed2002

Central nervous system effects of caffeine and adenosine on fatigue.

Caffeine ingestion can delay fatigue during exercise, but the mechanisms remain elusive. This study was designed to test the hypothesis that blockade of central nervous system (CNS) adenosine receptors may explain the beneficial effect of caffeine on fatigue. Initial experiments were done to confirm an effect of CNS caffeine and/or the adenosine A(1)/A(2) receptor agonist 5'-N-ethylcarboxamidoadenosine (NECA) on spontaneous locomotor activity. Thirty minutes before measurement of spontaneous activity or treadmill running, male rats received caffeine, NECA, caffeine plus NECA, or vehicle during four sessions separated by approximately 1 wk. CNS caffeine and NECA (intracerebroventricular) were associated with increased and decreased spontaneous activity, respectively, but caffeine plus NECA did not block the reduction induced by NECA. CNS caffeine also increased run time to fatigue by 60% and NECA reduced it by 68% vs. vehicle. However, unlike the effects on spontaneous activity, pretreatment with caffeine was effective in blocking the decrease in run time by NECA. No differences were found after peripheral (intraperitoneal) drug administration. Results suggest that caffeine can delay fatigue through CNS mechanisms, at least in part by blocking adenosine receptors.

Adenosine-5'-(N-ethylcarboxamide)↗