Hematological, serum biochemical parameters, and physiological responses to acute stress of Beluga sturgeon (Huso huso, Linnaeus 1785) juveniles fed dietary nucleotide

The present study aimed to investigate the effects of dietary nucleotide on serum biochemical and hematological parameters as well as stress response in Beluga sturgeon Huso huso juveniles. Fish (12.6?±?0.5?g) were fed diets containing 0%, 0.15%, 0.25%, 0.35%, and 0.50% nucleotide over a 62-day period. The experiment was carried out in 600-L tanks with 30 fish per tank. Fish were fed five times a day until apparent satiation. At the end of the experiment, blood samples were collected from treatments for investigation of biochemical and hematological parameters. Then, fish were subjected to an acute stress. Blood samples were collected at 0 and 6?h post stress, and plasma cortisol and glucose levels were determined. The results showed that total protein, cholesterol, triglycerides, albumin, and globulin were not affected by dietary nucleotide (P?>?0.05). Hematocrit and hemoglobin values were significantly higher in the 0.35% treatment compared to those of the control (P?<?0.05). Beluga juveniles fed 0.5% dietary nucleotide had a significantly lower hemoglobin value (P?<?0.05). Lymphocyte proportion was significantly higher in the 0.25 and 0.35 nucleotide groups than in the control group (P?<?0.05). Cortisol and glucose levels in all groups were significantly affected by time; nevertheless, in fish fed nucleotides, stress-induced cortisol elevation was lower compared to that of the control group (P?<?0.05). The results indicated that dietary nucleotide supplementation was capable of affecting hematological parameters and physiological stress responses of Beluga juveniles.     

Changes in blood biochemistry of common carp Cyprinus carpio (Linnaeus), following exposure to different concentrations of clove solution

The effect of different concentrations of clove solution on blood biochemistry of common carp Cyprinus carpio was investigated. Fish were exposed to 700, 1,000, 2,000, 3,000, 4,000, and 5,000 ppm clove solution over a period of 300, 200, 150, 100, 75, and 70 s, respectively, to reach stage 4 anesthesia. Immediately after induction, blood samples were collected to determine biochemical characteristics. Results showed significant (P?<?0.0001) changes in serum cortisol and glucose levels; however, no significant changes were found in serum levels of triglyceride, total protein, cholesterol, albumin, calcium, chloride, or sodium. Serum levels of cortisol and glucose were similar (P?>?0.05) in fish exposed to concentrations 4,000 and 5,000 ppm of clove solution, which significantly increased while anesthetic concentration decreased, reaching maximum levels at 700 ppm. The results suggest that anesthesia using higher concentrations of clove solution (and over short period) is preferred compared to lower concentrations (and long period), in the case of stress response. However, the other tested parameters are not sensitive to the anesthesia protocol, at least under the conditions of the present study.     

Comparative efficacy of two anesthetic agents in the Sobaity sea bream,Sparidentex hasta (Valenciennes 1830)

It is known that responses to the same anesthetic can vary considerably among different fish species. In this investigation, the efficacy of two anesthetic agents (clove powder and 2-phenoxyethanol) was compared in Sobaity sea bream, Sparidentex hasta (Valenciennes 1830). Induction and recovery times for S. hasta anesthetized with anesthetic agents were dose-dependent (P?<?0.05). The onset of individual phases of anesthesia and recovery times depended significantly on the concentration of the anesthetic used (P?<?0.05). An inverse exponential relationship was observed between concentrations of anesthetic and induction time, whereas exponential relationships were observed between concentrations and recovery times for both anesthetic agents evaluated. The lowest effective concentrations based on the efficacy criteria of complete anesthetic induction within 180 s and recovery within 300 s were determined to be 100 mg?L^?1 (induction time 1.92?±?0.10 min and recovery time 2.48?±?0.17 min) for clove powder and 200 μL?L^?1 (induction time 2.55?±?0.14 min and recovery time 5.66?±?0.62 min) for 2-phenoxyethanol. Clove powder was proven to be more effective, and the latter appears to meet many of the criteria of an ideal anesthetic for this fish species.     

Evaluation of the antidiabetic and antioxidant potentials of methanolic leaf extract of Helianthus annuus L. on alloxan-induced hyperglycemic rats

Helianthus annuus (sunflower) is an annual plant native to America that possesses a large inflorescence. The present study evaluated the acute toxicity, antidiabetic, oral glucose tolerance test (OGTT), and antioxidant effects of methanol extract of H. annuus leaves using alloxan-induced diabetic rats. The extract at the dose range of 300–3,600 mg/kg was tolerated by the rats. The extract (150, 300, and 600 mg/kg) showed a significant (p?p?>?0.05) differences between the extract-treated groups and glibenclamide (2 mg/kg)-treated groups. At 6 h posttreatment, there was a significant (p?p?>?0.05) difference in blood glucose level among the treatment groups. In diabetic OGTT, the blood glucose level of the extract (600 mg/kg)-treated group was significantly (p?p?>?0.05) difference between the extract- and glibenclamide (2 mg/kg)-treated groups. The extract produced a concentration-dependent increase in antioxidant activity. These findings suggest that H. annuus has potent antidiabetic and antioxidant activities and validate its folkloric use in traditional medicine for the treatment of diabetes mellitus.     

Considerations for Use of Acupuncture as Supplemental Therapy for Patients with Allergic Asthma

This study examines the clinical and immunomodulatory effects of acupuncture in the treatment of patients with allergic asthma. The acupuncture points GV14, BL12, and BL13 were selected based on the theory of traditional Chinese medicine in treating asthma. Manual acupuncture was performed once every other day (three times per week) for 5 weeks. The needles were twisted approximately 360° evenly at the rate of 60 times/min for 20 s, manipulated every 10 min and withdrawn after 30 min. Concentrations of sIgA and total IgA in secretions were determined by the combination of sucrose density gradient ultracentrifugation and RIA. Levels of cortisol in the plasma were measured by RIA. Total IgE in the sera was examined by ELISA. Flow cytometry was used to detect the numbers of CD3+, CD4+, CD8+, and IL-2R + T lymphocytes in the peripheral blood. The absolute and differential numbers of eosinophils in peripheral blood were counted with eosin staining. The total efficacy of the acupuncture treatment in patients with allergic asthma at the end of one course of treatment was 85 %. After treatment, the concentrations of sIgA and total IgA in the saliva (P?<?0.01, P?<?0.02) and nasal secretions (P?<?0.02, P?<?0.02) were significantly decreased in patients with allergic asthma. The levels of total IgE in sera (P?<?0.001), the counts of IL-2R + T lymphocytes (P?<?0.001), and the absolute and differential numbers of eosinophils (P?<?0.01, P?<?0.01) in the peripheral blood were also significantly decreased. The numbers of CD3+, CD4+, and CD8+ T lymphocytes in the peripheral blood were significantly increased in the allergic asthmatics treated by acupuncture (P?<?0.001, P?<?0.01, and P?<?0.001, respectively). The concentration of cortisol in the plasma of asthmatic patients did not change significantly after the acupuncture treatment (P?>?0.05). Acupuncture has regulatory effects on mucosal and cellular immunity in patients with allergic asthma and may be an adjunctive therapy for allergic asthma.     

No effect of menstrual cycle phase on glucose and glucoregulatory endocrine responses to prolonged exercise

Introduction

Prolonged exercise requires increased utilization of blood glucose and adjustment of glucoregulatory hormones. Estrogen can reduce hepatic gluconeogenesis which could affect insulin concentrations. Amylin is co-secreted with insulin and controls influx of glucose into the blood.

Purpose

To determine the effect of menstrual cycle stage on glucose, leptin, and pancreatic hormone responses to prolonged (90 min) exercise.

Methods

Five healthy, eumenorrheic women (24.6 ± 5.1 years; 67.4 ± 1 kg) were monitored for 3 months to determine menstrual cycle length. Subjects completed a preliminary session to determine exercise workloads and, in a fasted condition, completed two randomized 90-min treadmill exercise trials at 60 % VO_2max during the early follicular (EFX) and mid-luteal phase (MLX) of their menstrual cycle. Blood samples were analyzed for glucose, insulin, C-peptide, amylin, glucagon, leptin, and cortisol concentrations at rest (?30 and 0 min), during exercise (18, 36, 54, 72, and 90 min) and after 20 min of recovery.

Results

No changes in amylin, leptin, or cortisol occurred for EFX and MLX trials. A significant (p < 0.05) time effect occurred for glucose, insulin, and glucagon with reduced insulin across the exercise trial and increases in glucose and glucagon later in the trial, but there were no differences between the EFX and MLX trials.

Conclusions

Menstrual cycle stage does not affect glucose, insulin, C-peptide, amylin, glucagon, cortisol, and leptin responses to prolonged exercise; however, the exercise reduces insulin and increases glucose and glucagon concentrations. This is the first study to determine acute effects of exercise on amylin and other glucoregulatory hormone responses in women.     

Effect of acute crowding stress on subsequent osmotic challenge and recovery in juvenile common carp Cyprinus carpio (Linnaeus)

Effect of acute crowding stress (density of 25?g/L for 2 and 4?h) on subsequent salinity (8?g/L) tolerance was investigated in juvenile common carp (Cyprinus carpio). To assess osmoregulatory conditions, blood cortisol, glucose, Na⁺ and Cl^? concentrations were measured at 0, 6, 24 and 72?h after osmotic challenge in three groups: control, and groups stressed for 2 and 4?h. Results indicated typical stress responses after crowding stress. In both stressed groups, cortisol was significantly higher than the control group, but no significant difference was observed within the stressed groups. Additionally, glucose levels increased after crowding stress, and there was a significant increase in the in 4-h group compared with the 2-h group. Ion concentration was not significantly affected by crowding stress. Osmotic challenge led to an increase in cortisol and glucose concentrations in unstressed fish, after 6?h, but in stressed fish, no change occurred in cortisol and glucose levels at this point compared to the pre-challenge values. There was no significant change in cortisol and glucose values at 6, 24 and 72?h after the osmotic challenge between groups. Cortisol and glucose returned to pre-stress values by 72?h following the challenge. In all groups, Na⁺ concentration significantly increased at 6?h after the osmotic challenge and stayed elevated until 72?h; however, there was no significant difference between groups at any time point. There was no significant difference in Cl^? concentrations between groups or sampling time points. These results indicate that the common carp is a hyperosmotic regulator after exposure to saline medium, and acute crowding stress does not impair osmotic stress response.     

Examining the mediating roles of binge eating and emotional eating in the relationships between stress and metabolic abnormalities

To test whether binge eating and emotional eating mediate the relationships between self-reported stress, morning cortisol and the homeostatic model of insulin resistance and waist circumference. We also explored the moderators of gender and age. Data were from 249 adults (mean BMI = 26.9 ± 5.1 kg/m²; mean age = 28.3 ± 8.3 years; 54.2 % male; 69.5 % white) recruited from the community who were enrolled in a cross-sectional study. Participants completed a comprehensive assessment panel of psychological and physiological assessments including a morning blood draw for plasma cortisol. We found negative relationships between stress and morning cortisol (r = ?0.15 to ?0.21; p < 0.05), and cortisol and the homeostatic model of insulin resistance and waist circumference (r = ?0.16, ?0.25, respectively; p < 0.05). There was not statistical support for binge eating or emotional eating as mediators and no support for moderated mediation for either gender or age; however, gender moderated several paths in the model. These include the paths between perceived stress and emotional eating (B = 0.009, p < 0.001), perceived stress and binge eating (B = 0.01, p = 0.003), and binge eating and increased HOMA-IR (B = 0.149, p = 0.018), which were higher among females. Among women, perceived stress may be an important target to decrease binge and emotional eating. It remains to be determined what physiological and psychological mechanisms underlie the relationships between stress and metabolic abnormalities.     

Selected biochemical parameters in plasma of blood and semen of Persian sturgeon,Acipenser persicus

The investigation of blood and seminal plasma biochemical parameters is essential for fish stock conservation and development of artificial propagation methods via extender improvement. In this research, comparison of blood and seminal plasma compounds and their relationship in Persian sturgeon, Acipenser persicus, were studied. Seminal plasma contained 59.53?±?2.56 mEq/l sodium (Na⁺), 4.72?±?0.31 mEq/l potassium (K⁺), 1.45?±?0.075 mEq/l chloride (Cl^?), 9.1?±?1.42 mEq/l calcium (Ca²⁺), 0.7?±?0.072 mEq/l magnesium (Mg²⁺), 0.11?±?0.021 g/dl total protein, 6.67?±?1.04 mg/dl cholesterol, 15.2?±?0.65 mg/dl triacylglycerol, and 18.22?±?4.16 mg/dl glucose. Also, blood biochemical values were determined (mean?±?SEM) for Na⁺ (123.2?±?1.31 mEq/l), K⁺ (2.77?±?0.088 mEq/l), Cl^? (97.18?±?1.23 mEq/l), Ca²⁺ (6.67?±?0.24 mEq/l), Mg²⁺ (1.29?±?0.074 mEq/l), glucose (198.49?±?18.03 mg/dl), triacylglycerol (214.22?±?13.38 mg/dl), total protein (3.62?±?0.23 g/dl), and cholesterol (127.11?±?6.94 mg/dl). The mean blood and seminal osmolality values were 244.62?±?3.66 and 86.9?±?4.22 mOsm/kg, respectively. Results of the comparison between biochemical parameters of seminal and blood plasma indicated that the concentrations of all parameters of blood plasma were significantly (P?++ and Na⁺ of the seminal plasma (P?P?相似文献   

Chloride cell morphometrics of Common carp, Cyprinus carpio, in response to different salinities

Salinity plays an important role in the survival, metabolism, and distribution of fish during development. The successful establishment of species in a given habitat depends upon the ability of each developmental stage to cope with salinity via osmoregulation. The present study was conducted to assess the effect of salinity on number and size of chloride cells or mitochondria rich cells and their relation to osmoregulatory ability in Cyprinus carpio, a freshwater (FW) fish. No mortality occurred when the Common carp was gradually transferred into brackish water. Branchial chloride cell numbers decreased after brackish water exposure, whereas a gradual increase was observed in chloride cell size. Chloride cells exist in both FW and brackish water. The number of chloride cell fish in 9 ppt salinity was greatly significant (p < 0.05) when compared with other treatments, while chloride cells with larger size were observed in 12 ppt salinity (p < 0.05). Hence, our data indicate that in culture conditions, adult Common carp can survive successfully in brackish water with salinity of up to 9 ppt.     

Hematological and biochemical responses of common carp Cyprinus carpio to direct infusion of crude oil

Crude oil is one of the dangerous pollutants within water ecosystems. The purpose of current research was to determine the controlled effects of LC_50–96h dose (22.4?±?0.03 ppm) of crude oil for 0, 24, 48, and 96 h on hematological and biochemical indices of juvenile common carp. Results showed significant elevation in the white blood cell (WBC) and red blood cell (RBC; P?<?0.01). Exposure to crude oil significantly increased hemoglobin and hematocrite (P?<?0.01). Among RBC indices, only mean corpuscular hemoglobin concentration was not significantly different and both mean corpuscular volume and mean cell hemoglobin showed significant elevation after exposure (P?<?0.01). Just neutrophil and lymphocyte were found within WBC indices and both of them significantly changed (P?<?0.01). Among biochemical indices, in contrast to glucose, cortisol significantly elevated.     

Low-volume,high-intensity,aerobic interval exercise for sedentary adults: \dot{V}O2max,cardiac mass,and heart rate recovery

Purpose

The aim of this study was to compare the effects of low-volume, high-intensity aerobic interval training (HAIT) on maximal oxygen consumption ( \(\dot{V}\) O_2max), left ventricular (LV) mass, and heart rate recovery (HRR) with high-volume, moderate-intensity continuous aerobic training (CAT) in sedentary adults.

Methods

Twenty-four healthy but sedentary male adults (aged 29.2 ± 7.2 years) participated in an 8-week, 3-day a week, supervised exercise intervention. They were randomly assigned to either HAIT (18 min, 180 kcal per exercise session) or CAT (45 min, 360 kcal). \(\dot{V}\) O_2max, LV mass (3T-MRI), and HRR at 1 min (HRR-1) and 2 min (HRR-2) after maximal exercise were measured pre- and post-intervention.

Results

Changes in \(\dot{V}\) O_2max during the 8-week intervention were significant (P < 0.01) in both groups (HAIT, 8.7 ± 3.2 ml kg^?1 min^?1, 22.4 ± 8.9 %; CAT, 5.5 ± 2.8 ml kg^?1 min^?1, 14.7 ± 9.5 %), while the \(\dot{V}\) O_2max improvement in HAIT was greater (P = 0.02) than in CAT. LV mass in HAIT increased (5.1 ± 8.4 g, 5.7 ± 9.1 %, P = 0.05), but not in CAT (0.9 ± 7.8 g, 1.1 ± 8.4 %, P = 0.71). While changes in HRR-1 were not significant in either group, change in HRR-2 for HAIT (9.5 ± 6.4 bpm, 19.0 ± 16.0 %, P < 0.01) was greater (P = 0.03) than for CAT (1.6 ± 10.9 bpm, 3.9 ± 16.2 %, P = 0.42).

Conclusions

This study suggests that HAIT has potential as a time-efficient training mode to improve cardiorespiratory capacity and autonomic nervous system function in sedentary adults.     

Dietary docosahexaenoic acid to eicosapentaenoic acid ratios effects on hemato-immunological and plasma biochemical parameters in silvery-black porgy (<Emphasis Type="Italic">Sparidentex hasta</Emphasis>) juveniles

An 8-week feeding experiment was conducted in juvenile silvery-black porgy (Sparidentex hasta) (initial mean weight 20.1 ± 0.1 g, mean ± SD) to estimate the optimum dietary docosahexaenoic to eicosapentaenoic acid (DHA/EPA) ratio. Triplicate groups of fish (12 fish in each replicate) were kept into 15 cylindrical polyethylene tanks (250 L) at 18.7 °C and handfed by one of the five diets which formulated with graded ratios of DHA/EPA (0.2, 0.4, 0.9, 2.0, 3.3) two times daily. In the fillet and liver, DHA and DHA/EPA ratios significantly increased with increasing dietary DHA concentrations (P < 0.05). Fish fed the 0.2 DHA/EPA ratio diets had the highest hemolytic activity (P < 0.05). Plasma thiobarbituric acid reactive substance concentration, catalase activity, total antioxidant capacity, total cholesterol, and triglyceride significantly decreased with increasing dietary DHA/EPA ratios (P < 0.05). It is concluded that health status of silvery-black porgy juveniles were not influenced by dietary graded ratios of DHA/EPA.     

Hematotoxic effects of direct infusion of crude diesel oil on juvenile great sturgeon Huso huso

Changes in the hematological and immunological parameters of fish due to anthropological pollutants, may lead to hematotoxic and immunotoxic effects. The objectives of current study were to determine the experimental effects of direct infusion of crude diesel oil on hematological and immunological features of juvenile great sturgeon Huso huso. During this toxicity test, juveniles of beluga were exposed to the acute doses (5, 10, 20, 40, 100, 500, and 1,000 ppm) of direct infusion crude diesel oil for 0, 48 h and 7 days. WBC, MCH, MCHC, and neutrophil in fish exposed to crude diesel oil for 48 h were significantly greater compared to the respective control groups and RBC, Hb, Ht, MCV, and lymphocyte were significantly lower than control groups (P?≤?0.05). Eosinophils did not vary significantly in the groups exposed to 48 h crude diesel oil compared to the respective control groups (P?>?0.05). Furthermore, 7-day exposures showed that WBC and Neutrophil were significantly greater compared to the respective control groups (P?≤?0.05) and MCV was depleted within the crude diesel oil adjacency.     

Haematological reference ranges of cultured Clarias gariepinus in the Lower Benue River Basin,Nigeria

Blood samples were collected from 170 cultured African sharptooth catfish (Clarias gariepinus) to establish haematological baseline values of this important tropical pisciculture fish species in the Guinea savannah agro-ecological zone of Nigeria. The total red blood cell count and the total white blood cell count were obtained by haemocytometry, while the packed cell volume and haemoglobin were obtained by microhaematocrit and cyanomethmoglobin methods, respectively. The results obtained varied between gender and age and were as follows: total red blood cell count, 1.72?±?0.34?×?10⁶/mm³ in juveniles and 4.50?±?0.57?×?10⁶/mm³ in adults; total white blood cell count, 15.50?±?1.1510³/mm³in juvenile and 16.41?±?1.21?×?10³/mm³in adults; packed cell volume, 30.08?±?7.78 % in juveniles and 39.59?±?3.93 % in adults; haemoglobin, 9.43?±?3.45 g/dl in juveniles and 10.99?±?3.29 g/dl in the adults; mean corpuscular volume, 173.75?±?41.93 fl in juveniles and 87.01?±?14.37 fl in adults; mean corpuscular haemoglobin, 51.11?±?13.10 pg in the juveniles and 26.81?±?8.61 pg in the adults, while the mean corpuscular haemoglobin concentration values obtained are 32.61?±?10.42 g/dl in the juveniles and 33.80?±?10.0 g/dl in the adults.     

Urinary trypsin inhibitor suppresses excessive generation of superoxide anion radical, systemic inflammation, oxidative stress, and endothelial injury in endotoxemic rats

Objective and design

The protective effects of ulinastatin, a human urinary trypsin inhibitor (UTI), against superoxide radical (O ₂ ^?· ) generation, systemic inflammation, lipid peroxidation, and endothelial injury were investigated in endotoxemic rats.

Materials and treatment

Twenty-one Wistar rats were allocated to a control group, a UTI group, and a sham group. A bolus of lipopolysaccharide (LPS; 3 μg/g) was administered intravenously to the control group, a bolus of LPS and UTI (5 U/g) to the UTI group, and a bolus of saline to the sham group.

Methods

The O ₂ ^?· generated was measured as the current in the right atrium using an electrochemical O ₂ ^?· sensor. Plasma nitrite, high mobility group box 1 (HMGB1), tumor necrosis factor (TNF)-α, inteleukin (IL)-6, malondialdehyde, and soluble intercellular adhesion molecule-1 (sICAM-1) were measured 360 min after LPS administration.

Results

The O ₂ ^?· current increased in the control group and was significantly attenuated in the UTI group after 55 min (P < 0.05 at 55–60 min, P < 0.01 at 65–360 min). Plasma nitrite, HMGB1, TNF-α, IL-6, malondialdehyde, and sICAM-1 were attenuated in the UTI group.

Conclusions

UTI suppressed excessive O ₂ ^?· generation, systemic inflammation, lipid peroxidation, and endothelial injury in endotoxemic rats.     

Effects of ghrelin on some plasma hormonal changes in juvenile Persian sturgeon (Acipenser persicus)

The functions of ghrelin, a novel weight-regulatory peptide, have not been intensively investigated in primitive fish. This experiment was conducted to determine whether ghrelin has a specific effect on growth hormone (GH), prolactin and cortisol levels in Persian sturgeon (Acipenser persicus). Juvenile Persian sturgeons with a mean body weight of 320?±?30?g were given a single injection of ghrelin at three doses of 0.1, 1 and 10?ng/g body weight. Control animals were injected with vehicle (sterile saline) only. Blood samples were collected at 0, 2, 4, 8, 24, 48 and 72?h after injection. The level of plasma hormones were determined by ELISA kit. As expected, ghrelin injection significantly elevated plasma GH (P?<?0.05), whereas prolactin levels did not significantly change after injection (P?>?0.05). Plasma cortisol levels decreased in fish injected with high doses of ghrelin (P?<?0.05). Ghrelin at 10?ng/g body weight had the most influence on GH release, and 1?ng/g ghrelin injection caused the lowest level of cortisol. These results show for the first time that ghrelin induces some plasma hormonal changes in sturgeon fish, as lower vertebrates, but more investigations are needed in this area.     

The effect of water-soluble fraction of crude oil on serum biochemical changes in the great sturgeon Huso huso

Caspian Sea has oil treasure as well as fisheries resources. One the most precious resources of fisheries are sturgeons. Crude oil is a very dangerous pollutant of water ecosystems which are in possession of oil resources. In the present study, juveniles beluga were exposed to four indirect doses (0, 10, 100, 500, and 1,000 ppm) of water-soluble fraction (WSF) of crude oil for 0 h, 48 h, and 7 days. The results showed that after 48 h of exposure, all biochemical indices (glucose, triglyceride, calcium, and protein) significantly increased (P?≤?0.05). Furthermore, all biochemical indices showed significantly elevation after exposure to WSF of oil for 7 days (P?≤?0.01). Among enzymatic parameters in both sampling times, alkaline phosphatase decreased and the aminotransferase and alanine aminotransferase increased along with different doses of WSF of crude oil exposure.     

Combining heat stress and moderate hypoxia reduces cycling time to exhaustion without modifying neuromuscular fatigue characteristics

Purpose

This study investigated the isolated and combined effects of heat [temperate (22 °C/30 % rH) vs. hot (35 °C/40 % rH)] and hypoxia [sea level (FiO₂ 0.21) vs. moderate altitude (FiO₂ 0.15)] on exercise capacity and neuromuscular fatigue characteristics.

Methods

Eleven physically active subjects cycled to exhaustion at constant workload (66 % of the power output associated with their maximal oxygen uptake in temperate conditions) in four different environmental conditions [temperate/sea level (control), hot/sea level (hot), temperate/moderate altitude (hypoxia) and hot/moderate altitude (hot + hypoxia)]. Torque and electromyography (EMG) responses following electrical stimulation of the tibial nerve (plantar-flexion; soleus) were recorded before and 5 min after exercise.

Results

Time to exhaustion was reduced (P < 0.05) in hot (?35 ± 15 %) or hypoxia (?36 ± 14 %) compared to control (61 ± 28 min), while hot + hypoxia (?51 ± 20 %) further compromised exercise capacity (P < 0.05). However, the effect of temperature or altitude on end-exercise core temperature (P = 0.089 and P = 0.070, respectively) and rating of perceived exertion (P > 0.05) did not reach significance. Maximal voluntary contraction torque, voluntary activation (twitch interpolation) and peak twitch torque decreased from pre- to post-exercise (?9 ± 1, ?4 ± 1 and ?6 ± 1 % all trials compounded, respectively; P < 0.05), with no effect of the temperature or altitude. M-wave amplitude and root mean square activity were reduced (P < 0.05) in hot compared to temperate conditions, while normalized maximal EMG activity did not change. Altitude had no effect on any measured parameters.

Conclusion

Moderate hypoxia in combination with heat stress reduces cycling time to exhaustion without modifying neuromuscular fatigue characteristics. Impaired oxygen delivery or increased cardiovascular strain, increasing relative exercise intensity, may have also contributed to earlier exercise cessation.