Physiological and muscle histochemical assessment of men and women 10 km runners matched for race performance or training volume.

Women have a disadvantage for performance in long-distance running compared with men. To elaborate on inherent characteristics, 12 subelite women were matched with 12 men for training volume (M-Tm) (56.6 ± 18 vs. 55.7 ± 17 km/wk). The women were also matched to other men for a 10 km staged outdoor time trial (M-Pm) (42:36 min:s) to determine which factors could explain equal running performance. Anthropometry and treadmill tests were done. Fiber type (% Type I and Type IIA) and citrate synthase activities were analyzed in muscle biopsy samples. Consistent sex differences for both comparisons included height, weight, % body fat (P < 0.01), and hematocrit (P < 0.05). Women had lower V̇o2max and peak treadmill speed (PTS) compared with both M-Tm and M-Pm (P < 0.01). Training matched pairs had no sex difference in % PTS at race pace but compared with M-Pm women ran at a higher % PTS (P < 0.05) and %HRmax (P < 0.01) at race pace. On average, the women trained 22.9 km/wk more than M-Pm (+67.5%, P < 0.01). This training was not associated with higher V̇o2max or better running economy. Muscle morphology and oxidative capacity did not differ between groups. Percentage body fat remained significantly higher in women. In conclusion, women matched to men for training volume had slower 10 km performance (-10.5% P < 0.05). Higher training volume, more high-intensity sessions/wk, and time spent training in the 95%-100% HRmax zone may explain the higher % PTS and %HRmax at race pace in women compared with performance-matched men.NEW & NOTEWORTHY When subelite women 10 km runners were matched with male counterparts for 10 km race performance, inherent differences in % body fat, V̇o2max, Hct, and peak treadmill speed were counteracted by significantly higher training volume, more time training at higher %HRmax and consequently, higher %HRmax and %PTS at race pace. Citrate synthase activity and muscle fiber types did not differ. When women and men matched for training, 10 km performance of men was 10.5% faster.

Skeletal muscle fibre type and enzymatic activity in adult offspring following placental and peripheral malaria exposure in foetal life.

Background: Maternal malaria may restrict foetal growth. Impaired utero-placental blood flow due to malaria infection may cause hypoxia-induced altered skeletal muscle fibre type distribution in the offspring, which may contribute to insulin resistance and impaired glucose metabolism. This study assessed muscle fibre distribution 20 years after placental and/or peripheral in-utero malaria exposure compared to no exposure, i.e., PPM+, PM+, and M-, respectively. Methods: We traced 101 men and women offspring of mothers who participated in a malaria chemosuppression study in Muheza, Tanzania. Of 76 eligible participants, 50 individuals (29 men and 21 women) had skeletal muscle biopsy taken from m. vastus lateralis in the right leg. As previously reported, fasting and 30 min post-oral glucose challenge plasma glucose values were higher, and insulin secretion disposition index was lower, in the PPM+ group. Aerobic capacity (fitness) was estimated by an indirect VO2max test on a stationary bicycle. Muscle fibre sub-type (myosin heavy chain, MHC) distribution was analysed, as were muscle enzyme activities (citrate synthase (CS), 3-hydroxyacyl-CoA dehydrogenase, myophosphorylase, phosphofructokinase, lactate dehydrogenase, and creatine kinase activities. Between-group analyses were adjusted for MHC-I %. Results: No differences in aerobic capacity were found between groups. Despite subtle elevations of plasma glucose levels in the PPM+ group, there was no difference in MHC sub-types or muscle enzymatic activities between the malaria-exposed and non-exposed groups. Conclusion: The current study did not show differences in MHC towards glycolytic sub-types or enzymatic activity across the sub-groups. The results support the notion of the mild elevations of plasma glucose levels in people exposed to placental malaria in pregnancy being due to compromised pancreatic insulin secretion rather than insulin resistance.

Therapeutic Benefit in Rheumatoid Cachexia Illustrated Using a Novel Primary Human Triple Cell Coculture Model.

Background: The loss of muscle mass in rheumatoid arthritis (RA), termed rheumatoid cachexia, is predicted to result from the complex interactions between different cell types involved in the maintenance of skeletal muscle mass, namely, myoblasts, fibroblasts, and macrophages. The complexity within the muscle is further highlighted by the incidence of nonresponsiveness to current RA treatment strategies. Method: This study aimed at determining differences in the cellular responses in a novel human primary cell triple coculture model exposed to serum collected from nonarthritic controls (NC), RA treatment naïve (RATN), and RA treatment-nonresponding (RATNR) patients. Bone morphogenetic protein-7 (BMP-7) was investigated as a treatment option. Results: Plasma analysis indicated that samples were indeed representative of healthy and RA patients-notably, the RATNR patients additionally exhibited dysregulated IL-6/IL-10 correlations. Coculture exposure to serum from RATNR patients demonstrated increased cellular growth (p < 0.001), while both hepatocyte growth factor (p < 0.01) and follistatin (p < 0.001) were reduced when compared to NC. Furthermore, decreased concentration of markers of extracellular matrix formation, transforming growth factor-ß (TGF-ß; p < 0.05) and fibronectin (p < 0.001), but increased collagen IV (p < 0.01) was observed following RATNR serum exposure. Under healthy conditions, BMP-7 exhibited potentially beneficial results in reducing fibrosis-generating TGF-ß (p < 0.05) and fibronectin (p < 0.05). BMP-7 further exhibited protective potential in the RA groups through reversing the aberrant tendencies observed especially in the RATNR serum-exposed group. Conclusion: Exposure of the triple coculture to RATN and RATNR serum resulted in dysregulated myoblast proliferation and growth, and ECM impairment, which was reversed by BMP-7 treatment.

Unresolved intramuscular inflammation, not diminished skeletal muscle regenerative capacity, is at the root of rheumatoid cachexia: insights from a rat CIA model.

Rheumatoid arthritis targets numerous organs in patients, including the skeletal muscle, resulting in rheumatoid cachexia. In the muscle niche, satellite cells, macrophages, and myofibroblasts may be affected and the factors they release altered. This study aimed to assess these cell types, cytokines, and growth factors and their relationships to muscle fiber size and number in a rodent collagen-induced arthritis (CIA) model, in order to identify new therapeutic targets. Fiber cross-sectional area (CSA) was 57% lower in CIA than controls (p < 0.0001), thus smaller but more fibers visible per field of view. Immunostaining indicated the increased presence of satellite cells, macrophages, myofibroblasts, and myonuclei per field of view in CIA (p < 0.01), but this finding was not maintained when taking fiber number into consideration. Western blots of gastrocnemius samples indicated that tumor necrosis factor-α was significantly elevated (p < 0.01) while interleukin-10 (IL-10) was decreased (p < 0.05) in CIA. This effect was maintained (and heightened for IL-10) when expressed per fiber number. Myogenic regulatory factors (MyoD and myogenin), transforming growth factor-ß and inhibitor of differentiation were significantly elevated in CIA muscle and levels correlated significantly with CSA. Several of these factors remained elevated, but bone morphogenetic protein-7 decreased when considering fiber number per area. In conclusion, CIA-muscle demonstrated a good regenerative response. Myoblast numbers per fiber were not elevated, suggesting their activity results from the persistent inflammatory signaling which also significantly hampered maintenance of muscle fiber size. A clearer picture of signaling events at cellular level in arthritis muscle may be derived from expressing data per fiber.

Co-culture of pro-inflammatory macrophages and myofibroblasts: Evaluating morphological phenotypes and screening the effects of signaling pathway inhibitors.

Skeletal muscle regeneration is a complex process influenced by non-myogenic macrophages and fibroblasts, which acquire different phenotypes in response to changes in the injury milieu or changes in experimental conditions. In vitro, serum stimulates the differentiation of fibroblasts into myofibroblasts, while lipopolysaccharide (LPS) stimulates the polarization of unstimulated (M0) macrophages to acquire an M1 pro-inflammatory phenotype. We characterized these phenotypes using morphology (with circularity as shape descriptor; perfect circularity = 1.0) and phenotype-specific markers. Myofibroblasts (high α-smooth muscle actin [SMA] expression) had high circularity (mean 0.60 ± 0.03). Their de-differentiation to fibroblasts (low α-SMA expression) significantly lessened circularity (0.47 ± 0.01 and 0.35 ± 0.02 in 2% or 0% serum culture media respectively (p < 0.05). Unstimulated (M0) macrophages (no CD86 expression) had high circularity (0.72 ± 0.02) which decreased when stimulated to M1 macrophages (CD86 expression) (LPS; 0.61 ± 0.02; p < 0.05). Utilizing these established conditions, we then co-cultured M1 macrophages with myofibroblasts or myoblasts. M1 macrophages significantly decreased relative myofibroblast numbers (from 223 ± 22% to 64 ± 7%), but not myoblast numbers. This pro-inflammatory co-culture model was used to rapidly screen the following four compounds for ability to prevent M1 macrophage-mediated decrease in myofibroblast numbers: L-NAME (inducible nitric oxide synthase inhibitor), SB203580 (p38 mitogen-activated protein kinase inhibitor), SP600125 (c-Jun N-terminal kinase inhibitor) and LY294002 (phosphoinositide 3-kinase [PI3K] inhibitor). We found that LY294002 rescued myofibroblasts and decreased macrophage numbers. Myofibroblast rescue did not occur with L-NAME, SB203580 or SP600125 incubation. In conclusion, these data suggest a PI3K-associated mechanism whereby myofibroblasts can be rescued, despite simulated pro-inflammatory conditions.

Interleukin-6 Induces Myogenic Differentiation via JAK2-STAT3 Signaling in Mouse C2C12 Myoblast Cell Line and Primary Human Myoblasts.

Postnatal muscle growth and exercise- or injury-induced regeneration are facilitated by myoblasts. Myoblasts respond to a variety of proteins such as cytokines that activate various signaling cascades. Cytokines belonging to the interleukin 6 superfamily (IL-6) influence myoblasts' proliferation but their effect on differentiation is still being researched. The Janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathway is one of the key signaling pathways identified to be activated by IL-6. The aim of this study was to investigate myoblast fate as well as activation of JAK-STAT pathway at different physiologically relevant IL-6 concentrations (10 pg/mL; 100 pg/mL; 10 ng/mL) in the C2C12 mouse myoblast cell line and primary human myoblasts, isolated from eight young healthy male volunteers. Myoblasts' cell cycle progression, proliferation and differentiation in vitro were assessed. Low IL-6 concentrations facilitated cell cycle transition from the quiescence/Gap1 (G0/G1) to the synthesis (S-) phases. Low and medium IL-6 concentrations decreased the expression of myoblast determination protein 1 (MyoD) and myogenin and increased proliferating cell nuclear antigen (PCNA) expression. In contrast, high IL-6 concentration shifted a larger proportion of cells to the pro-differentiation G0/G1 phase of the cell cycle, substantiated by significant increases of both MyoD and myogenin expression and decreased PCNA expression. Low IL-6 concentration was responsible for prolonged JAK1 activation and increased suppressor of cytokine signaling 1 (SOCS1) protein expression. JAK-STAT inhibition abrogated IL-6-mediated C2C12 cell proliferation. In contrast, high IL-6 initially increased JAK1 activation but resulted in prolonged JAK2 activation and elevated SOCS3 protein expression. High IL-6 concentration decreased interleukin-6 receptor (IL-6R) expression 24 h after treatment whilst low IL-6 concentration increased IL-6 receptor (IL-6R) expression at the same time point. In conclusion, this study demonstrated that IL-6 has concentration- and time-dependent effects on both C2C12 mouse myoblasts and primary human myoblasts. Low IL-6 concentration induces proliferation whilst high IL-6 concentration induces differentiation. These effects are mediated by specific components of the JAK/STAT/SOCS pathway.

Polyphenol supplementation: benefits for exercise performance or oxidative stress?

Supplement use among athletes is widespread, including non-traditional and biological compounds. Despite increasing research, a comprehensive and critical review on polyphenol supplementation and exercise is still lacking. This review is relevant for researchers directly involved in the topic, as well as those with a broad interest in athletic performance enhancement and sports nutrition. The purpose of this review is to present background information on groups of polyphenols and their derivatives because their differing chemical structures influence mechanisms of action; to discuss the potential of plant, fruit and vegetable-based biological supplements, high in polyphenol content, to affect exercise performance and biomarkers of oxidative stress and exercise-induced muscle damage; and to critically discuss the exercise studies and biomarkers used. Subjects in the studies reviewed were either sedentary, healthy individuals, or active, recreationally trained or well-trained athletes. Polyphenol supplementation in exercise studies included mainly extracts (multicomponent or purified), juices, infusions or an increased intake of polyphenol-rich foods. This review includes details of supplement doses and exercise test protocols. Many studies considered only the performance or one or two selected biomarkers of antioxidant capacity instead of a comprehensive choice of biomarkers to assess damage to lipids or proteins. Evidence is insufficient to make recommendations for or against the use of polyphenol supplementation (neither specific polyphenols nor specific doses) for either recreational, competitive or elite athletes. Polyphenols have multiple biological effects, and future exercise studies must be designed appropriately and specifically to determine physiological interactions between exercise and the selected supplement, rather than considering performance alone.

Contusion injury with chronic in vivo polyphenol supplementation: leukocyte responses.

INTRODUCTION: In vivo, daily proanthocyanidolic oligomer (PCO) supplementation before and after experimental skeletal muscle contusion injury has been shown to result in a blunted neutrophil response in tissue, quicker macrophage infiltration into muscle, and faster recovery due to a left shift in time course of inflammation. The current study investigated effects of PCO on circulatory neutrophils and macrophage subpopulations as well as in vitro neutrophil migration. METHODS: Primary cultured neutrophils obtained from control animals were incubated in media with 20% conditioned plasma. To obtain conditioned media, male Wistar rats were supplemented with PCO (20 mg·kg(-1)d(-1)) or placebo (PLA) for 2 wk before a mass-drop contusion injury. Conditioned plasma was prepared from blood collected at different time points after injury (12 h, 1 d, 3 d, and 5 d). Macrophage subpopulation distribution, inflammatory cytokine, and myeloperoxidase levels were assessed for all time points. RESULTS: On day 1 postinjury, circulating neutrophil numbers were significantly lower in PLA than PCO, suggesting that extravasation from the blood was reduced by PCO. Concurrently, neutrophil migration in vitro was blunted in the presence of conditioned plasma from PCO supplemented rats compared with PLA supplemented rats. Plasma M1 and M2c macrophage numbers differed over time and between groups. M1 macrophage numbers peaked on day 3 with PCO supplementation, followed by a rise in M2c macrophages on day 5, when M1 macrophages numbers were still high in PLA. CONCLUSIONS: We conclude that PCO supplementation limits neutrophil migration capacity in vitro despite a chemotactic gradient. Furthermore, the earlier appearance of type M2 macrophages suggests a switch to an anti-inflammatory phenotype after injury even in circulation.

Accelerated skeletal muscle recovery after in vivo polyphenol administration.

Acute skeletal muscle damage results in fiber disruption, oxidative stress and inflammation. We investigated cell-specific contributions to the regeneration process after contusion-induced damage (rat gastrocnemius muscle) with or without chronic grape seed-derived proanthocyanidolic oligomer (PCO) administration. In this placebo-controlled study, male Wistar rats were subjected to PCO administration for 2 weeks, after which they were subjected to a standardised contusion injury. Supplementation was continued after injury. Immune and satellite cell responses were assessed, as well as oxygen radical absorption capacity and muscle regeneration. PCO administration resulted in a rapid satellite cell response with an earlier peak in activation (Pax7⁺, CD56⁺, at 4 h post-contusion) vs. placebo groups (PLA) (P<.001: CD56⁺ on Day 5 and Pax7⁺ on Day 7). Specific immune-cell responses in PLA followed expected time courses (neutrophil elevation on Day 1; sustained macrophage elevation from Days 3 to 5). PCO dramatically decreased neutrophil elevation to nonsignificant, while macrophage responses were normal in extent, but significantly earlier (peak between Days 1 and 3) and completely resolved by Day 5. Anti-inflammatory cytokine, IL-10, increased significantly only in PCO (Day 3). Muscle fiber regeneration (MHC(f) content and central nuclei) started earlier and was complete by Day 14 in PCO, but not in PLA. Thus, responses by three crucial cell types involved in muscle recovery were affected by in vivo administration of a specific purified polyphenol in magnitude (neutrophil), time course (macrophages), or time course and activation state (satellite cell), explaining faster effective regeneration in the presence of proanthocyanidolic oligomers.

Daily brief restraint stress alters signaling pathways and induces atrophy and apoptosis in rat skeletal muscle.

Skeletal muscle protein loss, known as atrophy, occurs during inactivity, disease, and aging. Atrophy may be the result of increased catabolic factors, e.g. glucocorticoids, or reduced influence of anabolic factors, e.g. insulin. The purpose of this study was to investigate atrophy, signaling mechanisms, and apoptosis in a rat model of restraint stress in 40 adult male Wistar rats. Due to the anxiolytic effects of Sutherlandia frutescens, we also determined if any of the molecular events in gastrocnemius muscle would be affected by daily treatment with S. frutescens. Rats were randomly assigned to four experimental groups: control placebo (CP); control Sutherlandia (CS) treatment; Restraint Placebo (RP) and Restraint Sutherlandia (RS) treatment. Restraint resulted in a significant increase in myostatin which was significantly reduced with Sutherlandia treatment. In addition, MyoD expression was significantly attenuated in RP and this effect was also counteracted by Sutherlandia treatment. Restraint also resulted in a significant attenuation of the PI3-Kinase/Akt signaling pathway and increased apoptosis which was reversed with Sutherlandia treatment. This study demonstrates for the first time that psychological stress elevates markers of muscle atrophy and apoptosis, whilst a herbal remedy, Sutherlandia, inhibits apoptosis, and signaling pathways associated with muscle atrophy.

Measurement reliability of highly variable physiological responses to experimentally-manipulated gas fractions.

Ventilatory and cardiac responses to changing inhaled gas fractions are notoriously variable within individuals. Such variation can confound clinical diagnoses and hypotheses about human adaptation. In this study we use a cardiac (HHR) and a ventilatory (HVR) measure of physiological sensitivity to an experimentally manipulated oxygen concentration (8% O2), to compare variation (a) within and between individuals, (b) within and between days and (c) within and between physiological parameters. To explore the sources of variation, we use the coefficient of variation (CV, %), repeatability (R, intraclass correlation coefficient, %) and repeated-measures analyses of variance. Both the HVR and the HHR are significantly repeatable (HVR: R = 0.76-0.92; HHR: R = 0.35-0.76) and equally variable within and between days. Its high R suggests that the HVR displays greater between-individual variation relative to within-individual variation than does the HHR. The HVR is thus a more reliable measure of physiological sensitivity to hypoxia than is the HHR. We suggest how these results may inform experimental design, and suggest how to avoid stochastic and experimental artefacts when investigating ventilatory and cardiac physiological responses to hypoxia.

Protecting muscle ATP: positive roles for peripheral defense mechanisms-introduction.

Skeletal muscle has evolved an impressive array of mechanisms for peripherally mediated control of ATP homeostasis. Some of these mechanisms are intracellular, and others are extracellular and include influences on the cross-bridge cycle itself and substrate supply. This paper introduces three distinctly different topics that nevertheless all have ATP defense in common. The role of ADP in fatigue is controversial but has recently been more clearly delineated so that an effect on alleviating force declines during extreme fatigue is plausible. AMP plays its role by activating the protein-kinase, AMPK, which is a key sensor of cellular energy stress. AMPK has different isoforms, is not uniformly distributed in the cell, and its activation is carefully controlled. It has multiple effects including improvements in substrate supply for the metabolic pathways producing ATP and inhibition of anabolic processes to further spare ATP. Red blood cells have the capacity to sense hypoxia and to release vasodilators where there is a locally increased demand for blood supply. The papers in this series emphasize the important positive roles of metabolites and sensors of fatigue in the balance between ATP supply and demand.

Can any metabolites partially alleviate fatigue manifestations at the cross-bridge?

During exercise, intracellular homeostasis depends on the matching of adenosine triphosphate (ATP) supply and ATP demand. Metabolites play a useful role in communicating the extent of ATP demand to the metabolic supply pathways. During fatigue from high-intensity exercise, a major change in the intracellular milieu of skeletal muscle is not ATP depletion but metabolite accumulation that affects the actomyosin cross-bridge interaction. The resulting reduction in myosin ATPase activity, cross-bridge turnover rate, and velocity of contraction can be considered a useful downregulation of ATP demand. Although maximal force is reduced, it is reduced less than myosin ATPase activity. In combination, efficiency of force production at the cross-bridge is thus enhanced. This is a second useful role for metabolites during fatigue because the total ATP cost per unit of force is partially reduced. Theoretical models predict that ADP may alleviate some effects of fatigue by further enhancing cross-bridge efficiency, thus providing a third useful role for metabolite accumulation. Recent experimental evidence reviewed here suggests that this occurs when ATP concentration is dramatically reduced. Single-fiber chemical analyses of fatigued muscle show lower ATP concentrations than other methods, but whether the appropriate microenvironments for effective competition by ADP for the nucleotide binding site occur around some or all of the cross-bridges remains technically difficult to prove at this time. During fatigue, muscle activation is also decreased, a response that potentially has the greatest effect on ATP demand-supply matching. I propose that the mismatch between the expected force production relative to muscle activation and the reduced force production from inorganic phosphate accumulation is the peripheral signal for reduced activation and is therefore the fourth useful role of metabolites in alleviating fatigue.

Antioxidant supplementation enhances neutrophil oxidative burst in trained runners following prolonged exercise.

The influence of an antioxidant vitamin supplement on immune cell response to prolonged exercise was determined using a randomized, double-blind, placebo-controlled, cross-over study. Twelve healthy endurance subjects (n = 6 male, n = 6 female; mean +/- SD for age, 30.1 +/- 6.2 yr; height, 1.76 +/- 7 m; body mass, 72.2 +/- 10.2 kg; VO2max, 63.7 +/- 12 ml x kg(-1) x min(-1)) participated in the study. Following a 3-week period during which subjects ingested a multivitamin and -mineral complex sufficient to meet the recommended daily allowance, they took either a placebo or an antioxidant vitamin supplement (containing 18 mg beta-carotene, 900 mg vitamin C, and 90 mg vitamin E) for 7 days prior to a 2-h treadmill run at 65% VO2max. Blood samples were drawn prior to and immediately following exercise. These were analyzed for neutrophil oxidative burst activity, cortisol and glucose concentrations, and white blood cell counts, as well as serum anti-oxidant vitamin concentrations. Plasma vitamin C, vitamin E, and beta-carotene concentrations significantly increased following 7-day supplementation (p < .05). In comparison to the placebo group, neutrophil oxidative burst was significantly higher following exercise (p < .05), but no differences were found in any other parameter following the 7-day supplementation period. Although the impact of exercise on neutrophil function is multifactorial, our data suggest that antioxidant supplementation may be of benefit to endurance athletes for the maintenance of this particular function of the innate immune system following the 7-day supplementation period.

Effect of an ADP analog on isometric force and ATPase activity of active muscle fibers.

The role played by ADP in modulating cross-bridge function has been difficult to study, because it is hard to buffer ADP concentration in skinned muscle preparations. To solve this, we used an analog of ADP, spin-labeled ADP (SL-ADP). SL-ADP binds tightly to myosin but is a very poor substrate for creatine kinase or pyruvate kinase. Thus ATP can be regenerated, allowing well-defined concentrations of both ATP and SL-ADP. We measured isometric ATPase rate and isometric tension as a function of both [SL-ADP], 0.1-2 mM, and [ATP], 0.05-0.5 mM, in skinned rabbit psoas muscle, simulating fresh or fatigued states. Saturating levels of SL-ADP increased isometric tension (by P'), the absolute value of P' being nearly constant, approximately 0.04 N/mm(2), in variable ATP levels, pH 7. Tension decreased (50-60%) at pH 6, but upon addition of SL-ADP, P' was still approximately 0.04 N/mm(2). The ATPase was inhibited competitively by SL-ADP with an inhibition constant, K(i), of approximately 240 and 280 microM at pH 7 and 6, respectively. Isometric force and ATPase activity could both be fit by a simple model of cross-bridge kinetics.

In vitro interleukin-6 release in whole blood cultures in samples taken at rest from triathletes and professional rugby players.

The aim of this study was to investigate the endotoxin-induced interleukin-6 (IL-6) release in whole blood cultures from samples taken at rest, 24 h post-exercise, from a control group of recreationally trained individuals (C), a group of highly trained triathletes (TA) and a group of highly trained professional rugby players (RP). Fifteen RP [mean (SD): age 26 (3) years, height 1.90 (0.2) m, body mass 104.5 (12.2 kg)], 13 male TA [age 33 (5) years, height 1.78 (0.1) m, body mass 76.3 (12.6) kg] and eight recreationally active male volunteers [age 28 (6) years, height 1.80 (0.1) m, body mass 72.3 (7.3) kg] participated in the study. Plasma IL-6 concentration and in vitro IL-6 synthesis by whole blood cultures were measured in samples taken at rest. Plasma IL-6 concentration was significantly higher ( P<0.01) for the RP and TA groups than for C, as were the in vitro basal and endotoxin activated concentrations. However, after endotoxin stimulation, newly induced IL-6 concentration was significantly lower ( P<0.01) in the RP and TA than in the C group. Therefore, professional rugby players have a similar IL-6 release of whole blood cultures in vitro to that of triathletes. Specifically, mononuclear cells appear to be chronically activated to spontaneously release IL-6, but have a decreased capacity to respond to a further stimulus. Amongst possible explanations for this, the most likely is counter-regulation due to already elevated IL-6 release.