Muscle synergies of multidirectional postural control in astronauts on Earth after a long-term stay in space.

Movements of the human biological system have adapted to the physical environment under the 1-g gravitational force on Earth. However, the effects of microgravity in space on the underlying functional neuromuscular control behaviors remain poorly understood. Here, we aimed to elucidate the effects of prolonged exposure to a microgravity environment on the functional coordination of multiple muscle activities. The activities of 16 lower limb muscles of 5 astronauts who stayed in space for at least 3 mo were recorded while they maintained multidirectional postural control during bipedal standing. The coordinated activation patterns of groups of muscles, i.e., muscle synergies, were estimated from the muscle activation datasets using a factorization algorithm. The experiments were repeated a total of five times for each astronaut, once before and four times after spaceflight. The compositions of muscle synergies were altered, with a constant number of synergies, after long-term exposure to microgravity, and the extent of the changes was correlated with the increased velocity of postural sway. Furthermore, the muscle synergies extracted 3 mo after the return were similar in their activation profile but not in their muscle composition compared with those extracted in the preflight condition. These results suggest that the modularity in the neuromuscular system became reorganized to adapt to the microgravity environment and then possibly reoptimized to the new sensorimotor environment after the astronauts were reexposed to a gravitational force. It is expected that muscle synergies can be used as physiological markers of the status of astronauts with gravity-dependent change.NEW & NOTEWORTHY The human neuromuscular system has adapted to the gravitational environment on Earth. Here, we demonstrated that prolonged exposure to a microgravity environment in space changes the functional coordination of multiple muscle activities regarding multidirectional standing postural control. Furthermore, the amount of change led to a greater regulatory balancing activity needed for postural control immediately after returning to Earth and differences in muscular coordination before space flight and 3 mo after the return to Earth.

Protective effects of Enterococcus faecium strain R30 supplementation on decreased muscle endurance under disuse in rats.

NEW FINDINGS: What is the central question of this study? Does Enterococcus faecium strain R30 (R30), a new lactic acid bacterial strain for supplementation, attenuate shifts in the typology of whole muscle fibres from slow- to fast-twitch by altering the autonomic nervous system in atrophied skeletal muscles? What is the main finding and its importance? R30 supplementation may attenuate the shifts in the typology of whole muscle fibres from slow- to fast-twitch fibres by upregulating peroxisome proliferator-activated receptor-γ coactivator-1α and activating the calcineurin-nuclear factor of activated T-cells signalling pathway, thus ameliorating the decrease in muscle endurance associated with disuse. ABSTRACT: Enterococcus faecium strain R30 (R30), a new lactic acid bacterial strain for supplementation, was hypothesized to attenuate shifts in the typology of whole muscle fibres from slow- to fast-twitch fibres in atrophied skeletal muscles. We further postulated that the prevention of slow-to-fast fibre shifts would suppress the decreased muscle endurance associated with atrophy. To evaluate the protective effects of R30, we analysed slow-to-fast fibre shifts and disuse-associated reduced muscle endurance. R30 was administered to rats with an acclimation period of 7 days before hindlimb unloading (HU) for 2 weeks. The composition ratio of the fibre type and the expression levels of peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α), calcineurin and nuclear factor of activated T-cells (NFAT) were measured. Muscle endurance was evaluated at the end of the 2-week HU period in an in situ environment. R30 supplementation suppressed the slow-to-fast fibre switch and decreased the HU-induced expression of PGC-1α proteins and the deactivation of the calcineurin-NFAT pathway. Furthermore, R30 prevented a decrease in HU-associated muscle endurance in calf muscles. These results indicate that R30 supplementation may attenuate the shifts in the typology of whole muscle fibres from slow- to fast-twitch fibres via the upregulation of PGC-1α and the activation of the calcineurin-NFAT signalling pathway, thereby ameliorating the decrease in muscle endurance associated with disuse.

Mild hyperbaric oxygen exposure attenuates rarefaction of capillary vessels in streptozotocin-induced diabetic soleus muscle in rats.

We examined the effects of mild hyperbaric oxygen (mHBO) exposure on capillary rarefaction in skeletal muscles of rats with diabetes. Streptozotocin (100 mg/kg) was administered to male Wistar rats via the tail vein to prepare a diabetic model. These rats were divided into 2 groups: the group with mHBO exposure (1.25 atmospheres absolute (ATA) with 36% oxygen; 3 h/day) and the group without mHBO exposure. Age-matched rats were used as the control group. Eight weeks later, the soleus of the rats was removed and then analyzed. With the onset of diabetes mellitus, capillary number, diameter, and volume in the soleus of the rats with diabetes decreased compared with those of the rats in the control group. In addition, increased anti-angiogenic thrombospondin-1 (TSP-1) and decreased pro-angiogenic murine double minute 2 (MDM-2) protein expressions were observed in the rats with diabetes. Alternatively, mHBO exposure attenuated the decrease in capillary diameter and volume in skeletal muscles of rats with diabetes, suppressed the overexpression of TSP-1, and restored the MDM-2 expression. These results indicate the exposure of mHBO partially attenuates capillary rarefaction in diabetic soleus muscle.

Licorice flavonoid oil supplementation promotes a reduction of visceral fat in exercised rats.

BACKGROUND: The beneficial effect of exercise combined with licorice flavonoid oil supplementation on visceral fat was investigated. METHODS: Male Sprague-Dawley rats were divided into 4 groups: control, exercise (Ex), control with licorice flavonoid oil supplementation (LFO), and exercise with licorice flavonoid oil supplementation (ExLFO) groups. The rats in the Ex and ExLFO groups ran on a treadmill (20-degree incline at 20 m/min for 30 min/day) 5 times a week for 7 weeks, and those in the LFO and ExLFO groups were orally administered with licorice flavonoid oil daily using a feeding needle. RESULTS: Exercise or licorice flavonoid oil supplementation resulted in the reduction of the visceral fat mass and adipocyte size, respectively. In addition, exercise combined with licorice flavonoid oil supplementation more effectively decreased both measures. Exercise alone increased the ß-hydroxyacyl-CoA dehydrogenase (ß-HAD) and citrate synthase (CS) activities in the soleus and plantaris muscles, and licorice flavonoid oil supplementation alone increased the hepatic carnitine palmitoyl transferase-2 (CPT-2) activity. Furthermore, the combination of exercise and licorice flavonoid oil supplementation enhanced the both muscular ß-HAD and CS activities, and hepatic CPT-2 activity. CONCLUSIONS: These results suggest that exercise combined with licorice flavonoid oil supplementation may be effective to decrease visceral adipose tissue via enhancing skeletomuscular and hepatic fatty acids oxidative capacity.

Acute effects of lactic acid-fermented and enzyme-digested soybean on protein synthesis via mTOR signaling in the skeletal muscle.

Protein-containing nutrients result in the efficient hypertrophy of muscles by increasing muscle protein synthesis. Soybean is often ingested by athletes or individuals who exercise; however, it takes very long to be absorbed. Lactic acid-fermented and enzyme-digested (LFED) soybean is absorbed faster than untreated soybean. This study aims at determining muscle protein synthesis after ingesting a single bolus of soybean or LFED soybean produced by lactic acid bacteria and protease digestion. Eight-week-old overnight-fasted ICR mice were administered powdered or LFED soybean. Mice were euthanized at 7, 15, 30, 60, 90, and 120 min after soybean intake. We have demonstrated that LFED soybean administration was quicker in stimulating muscle protein synthesis by activating mammalian target of rapamycin (mTOR) signaling than orally ingesting untreated soybean in the gastrocnemius muscle. These results suggested that LFED soybean is a more efficient source of nutrition for muscle hypertrophy than untreated soybean.

Effects of mild hyperbaric oxygen on osteoporosis induced by hindlimb unloading in rats.

INTRODUCTION: Disuse-induced bone loss is caused by a suppression of osteoblastic bone formation and an increase in osteoclastic bone resorption. There are few data available for the effects of environmental conditions, i.e., atmospheric pressure and/or oxygen concentration, on osteoporosis. This study examined the effects of mild hyperbaric oxygen at 1317 hPa with 40% oxygen on unloading-induced osteoporosis. MATERIALS AND METHODS: Eighteen 8-week old male Wistar rats were randomly divided into three groups: the control for 21 days without unloading and mild hyperbaric oxygen (NOR, n = 6), the unloading for 21 days and recovery for 10 days without mild hyperbaric oxygen (HU + NOR, n = 6), and the unloading for 21 days and recovery for 10 days with mild hyperbaric oxygen (HU + MHO, n = 6). RESULTS: The cortical thickness and trabecular bone surface area were decreased in the HU + NOR group compared to the NOR group. There were no differences between the NOR and HU + MHO groups. Osteoclast surface area and Sclerostin (Sost) mRNA expression levels were decreased in the HU + MHO group compared to the HU + NOR group. These results suggested that the loss of the cortical and trabecular bone is inhibited by mild hyperbaric oxygen, because of an inhibition of osteoclasts and enhancement of bone formation with decreased Sost expression. CONCLUSIONS: We conclude that exposure to mild hyperbaric oxygen partially protects from the osteoporosis induced by hindlimb unloading.

Effects of Exposure to Mild Hyperbaric Oxygen on DSS-Induced Colonic Inflammation and Diarrhea in Rats.

PURPOSE: In rodents, dextran sulfate sodium (DSS)-induced diarrhea and colonic inflammation have similar symptoms to those of ulcerative colitis in humans. We examined the effects of exposure to mild hyperbaric oxygen (MHO) at an atmospheric pressure of 1317 hPa with 40% oxygen on DSS-induced diarrhea and colonic inflammation in rats. METHODS: Five-week-old male Kyoto Apc Delta (KAD) rats (n = 12) were administered 2% DSS through drinking water for 1 week. Subsequently, DSS-treated male rats were not subjected to any further treatment (n = 6) or exposed to MHO (n = 6) for 2 weeks. Age-matched KAD rats not subjected to DSS treatment or exposed to MHO were used as the control group (n = 6). RESULTS: Control rats did not exhibit diarrhea and colonic inflammation. However, DSS-treated rats exhibited diarrhea and colonic inflammation, regardless of exposure to MHO. Exposure to MHO for 2 weeks led to decreased incidence of diarrhea in DSS-treated rats (p < 0.05). Exposure to MHO had no effect on colonic inflammation in DSS-treated rats (p = 0.12). CONCLUSION: Exposure to MHO for 2 weeks can improve diarrhea but cannot attenuate colonic inflammation, possibly due to the short exposure duration (2 weeks) used in this study.

Effects of exposure to mild hyperbaric oxygen during unloading on muscle properties in rats.

This study investigated the effects of exposure to mild hyperbaric oxygen during unloading on the properties of the soleus muscle in rats, because exposure to mild hyperbaric oxygen enhances oxidative metabolism in cells and tissues. Therefore, exposure to mild hyperbaric oxygen should inhibit the unloading-induced degenerative changes in skeletal muscles. One group of 7-week-old male Wistar rats were unloaded by hindlimb suspension for 2 weeks (HU, n = 12). A second group of age-matched rats were exposed to mild hyperbaric oxygen at 1317 hPa with 40% oxygen for 3 h a day during hindlimb suspension (HU + MHO, n = 12). A third group of age-matched rats without hindlimb suspension and exposure to mild hyperbaric oxygen were assigned as the controls (WR, n = 12). Soleus muscle weight (per body weight), succinate dehydrogenase (SDH) activity, and peroxisome proliferator-activated receptor γ coactivator-1α (Pgc-1α) mRNA levels were lower in the HU and HU + MHO groups than in the WR group, and these were higher in the HU + MHO group than in the HU group. The unloading-induced type shift from type I to type IIA fibers was inhibited by exposure to mild hyperbaric oxygen during unloading. It is concluded that the unloading-induced decrease in soleus muscle weight (per body weight) and type shift from type I to type IIA fibers in the soleus muscle were partially inhibited by exposure to mild hyperbaric oxygen during unloading.

Transcutaneous carbon dioxide attenuates impaired oxidative capacity in skeletal muscle in hyperglycemia model.

Hyperglycemia impairs oxidative capacity in skeletal muscle. Muscle oxidative capacity is regulated by peroxisome proliferator-activated receptor-γ co-activator-1α (PGC-1α). Transcutaneous carbon dioxide (CO2) enhances PGC-1α expression in skeletal muscle. Therefore, the aim of this study was to clarify the effects of CO2 therapy on muscle oxidative capacity impaired by streptozotocin (STZ)-induced hyperglycemia. Eight-week-old male Wistar rats were randomly divided into 4 groups: control, CO2 treatment, STZ-induced hyperglycemia, and STZ-induced hyperglycemia treated with CO2. STZ-induced hyperglycemia resulted in a decrease of muscle oxidative capacity and decreased PGC-1α and cytochrome c oxidase subunit 4 (COX-4) expression levels; while, application of transcutaneous CO2 attenuated this effect, and enhanced the expression levels of endothelial nitric oxide synthesis (eNOS). These results indicate that transcutaneous CO2 improves impaired muscle oxidative capacity via enhancement of eNOS and PGC-1α-related signaling in the skeletal muscle of rats with hyperglycemia.

Mild hyperbaric oxygen: mechanisms and effects.

Adequate oxygen supply by exposure to mild hyperbaric oxygen at appropriately high atmospheric pressure (1266-1317 hPa) and increased oxygen concentration (35-40% oxygen) has a possibility of improving the oxidative metabolism in cells and tissues without barotrauma and excessive production of reactive oxygen species. Therefore, metabolic syndrome and lifestyle-related diseases, including type 2 diabetes and hypertension, in rats were inhibited and/or improved by exposure to mild hyperbaric oxygen. It accelerated the growth-induced increase in oxidative capacity of the skeletal muscle in rats and inhibited the age-related decrease in oxidative capacity of the skeletal muscle in mice. A decrease in dopaminergic neurons in the substantia nigra of mice with Parkinson's disease was inhibited by exposure to mild hyperbaric oxygen. This review describes the beneficial effects of exposure to mild hyperbaric oxygen on some metabolic diseases and their perspectives.

Protective effects of Brazilian propolis supplementation on capillary regression in the soleus muscle of hindlimb-unloaded rats.

The protective effects of Brazilian propolis on capillary regression induced by chronically neuromuscular inactivity were investigated in rat soleus muscle. Four groups of male Wistar rat were used in this study; control (CON), control plus Brazilian propolis supplementation (CON + PP), 2-week hindlimb unloading (HU), and 2-week hindlimb unloading plus Brazilian propolis supplementation (HU + PP). The rats in the CON + PP and HU + PP groups received two oral doses of 500 mg/kg Brazilian propolis daily (total daily dose 1000 mg/kg) for 2 weeks. Unloading resulted in a decrease in capillary number, luminal diameter, and capillary volume, and an increase in the expression of anti-angiogenic factors, such as p53 and TSP-1, within the soleus muscle. Brazilian propolis supplementation, however, prevented these changes in capillary structure due to unloading through the stimulation of pro-angiogenic factors and suppression of anti-angiogenic factors. These results suggest that Brazilian propolis is a potential non-drug therapeutic agent against capillary regression induced by chronic unloading.

Application of transcutaneous carbon dioxide improves capillary regression of skeletal muscle in hyperglycemia.

The purpose of the present study was to determine the effects of transcutaneous CO2 application on the blood flow and capillary architecture of the soleus muscle in rats with streptozotocin (STZ)-induced hyperglycemia. Wistar rats were randomly divided into four groups: control, control + CO2-treated, STZ-induced hyperglycemia, and STZ-induced hyperglycemia + CO2-treated groups. Blood flow in soleus muscle increased during the transcutaneous CO2 exposure, and continued to increase for 30 min after the treatment. In addition, the transcutaneous CO2 attenuated a decrease in capillary and the expression level of eNOS and VEGF protein, and an increase in the expression level of MDM-2 and TSP-1 protein of soleus muscle due to STZ-induced hyperglycemia. These results indicate that the application of transcutaneous CO2 could improve capillary regression via the change of pro- and anti-angiogenesis factors, which might be induced by an increase in blood flow.

Mild hyperbaric oxygen activates the proliferation of epidermal basal cells in aged mice.

The proliferation of epidermal basal cells decreases with age. This study examined the effects of exposure to mild hyperbaric oxygen on the proliferative activity of epidermal basal cells in aged mouse skin. Hairless mice aged 5, 34 and 55 weeks were exposed to mild hyperbaric oxygen at 1266 hPa with 36% oxygen for 6 h/day for 1 or 2 weeks. Skin samples were then collected from the back area to evaluate epidermal thickness and the number and proliferative activity of epidermal basal cells. Exposure to mild hyperbaric oxygen had no effect on the epidermal thickness, irrespective of age, but accelerated the proliferative activity of epidermal basal cells in aged mouse skin.

Mild hyperbaric oxygen inhibits the growth-related decline in skeletal muscle oxidative capacity and prevents hyperglycemia in rats with type 2 diabetes mellitus.

BACKGROUND: Humans and animals with type 2 diabetes mellitus (T2DM) exhibit low skeletal muscle oxidative capacity and impaired glucose metabolism. The aim of the present study was to investigate the effects of exposure to mild hyperbaric oxygen on these changes in obese rats with T2DM. METHODS: Five-week-old non-diabetic Long-Evans Tokushima Otsuka (LETO) and diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats were divided into normobaric (LETO-NB and OLETF-NB) and mild hyperbaric oxygen (LETO-MHO and OLETF-MHO) groups. The LETO-MHO and OLETF-MHO groups received 1266 hPa with 36% oxygen for 3 h daily for 22 weeks. RESULTS: Fasting and non-fasting blood glucose, HbA1c, and triglyceride levels were lower in the OLETF-MHO group than in the OLETF-NB group (P < 0.05). In the soleus muscle, peroxisome proliferator-activated receptor δ/ß (Pparδ/ß), Pparγ, and PPARγ coactivator-1α (Pgc-1α) mRNA levels were lower in the OLETF-NB group than in all other groups (P < 0.05), whereas myogenin (Myog) and myogenic factor 5 (Myf5) mRNA levels were higher in the OLETF-MHO group than in the LETO-NB and OLETF-NB groups (P < 0.05). The soleus muscles in the OLETF-NB group contained only low-oxidative Type I fibers, whereas those in all other groups contained high-oxidative Type IIA and Type IIC fibers in addition to Type I fibers. CONCLUSIONS: Exposure to mild hyperbaric oxygen inhibits the decline in skeletal muscle oxidative capacity and prevents the hyperglycemia associated with T2DM. Pgc-1α, Myog, and Myf5 mRNA levels appear to be closely associated with skeletal muscle oxidative capacity in rats with T2DM.

Mild hyperbaric oxygen inhibits the decrease of dopaminergic neurons in the substantia nigra of mice with MPTP-induced Parkinson's disease.

We examined whether exposure to mild hyperbaric oxygen inhibits the decrease of dopaminergic neurons in the substantia nigra of a neurotoxic animal model with Parkinson's disease. Mice injected with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine hydrochloride and probenecid twice a week were divided into two groups: mice with mild hyperbaric oxygen and those without. The mice with mild hyperbaric oxygen were exposed to 1317hPa with 45% oxygen for 3h, three times a week. The decrease in dopaminergic neurons of mice with Parkinson's disease was inhibited by 11 weeks of exposure to mild hyperbaric oxygen. We conclude that exposure to mild hyperbaric oxygen is effective in preventing the progression of Parkinson's disease.

Unloading-induced atrophy and decreased oxidative capacity of the soleus muscle in rats are reversed by pre- and postconditioning with mild hyperbaric oxygen.

Our aim was to determine the effects of pre- and/or postconditioning with mild hyperbaric oxygen (1.25 atmospheric pressure, 36% oxygen for 3 h/day) on the properties of the soleus muscle that was atrophied by hindlimb suspension-induced unloading. Twelve groups of 8-week-old rats were housed under normobaric conditions (1 atmospheric pressure, 20.9% oxygen) or exposed to mild hyperbaric oxygen for 2 weeks. Ten groups then were housed under normobaric conditions for 2 weeks with their hindlimbs either unloaded via suspension or not unloaded. Six groups subsequently were either housed under normobaric conditions or exposed to mild hyperbaric oxygen for 2 weeks: the suspended groups were allowed to recover under reloaded conditions (unrestricted normal cage activity). Muscle weights, cross-sectional areas of all fiber types, oxidative capacity (muscle succinate dehydrogenase activity and fiber succinate dehydrogenase staining intensity) decreased, and a shift of fibers from type I to type IIA and type IIC was observed after hindlimb unloading. In addition, mRNA levels of peroxisome proliferator-activated receptor γ coactivator-1α decreased, whereas those of forkhead box-containing protein O1 increased after hindlimb unloading. Muscle atrophy and decreased oxidative capacity were unaffected by either pre- or postconditioning with mild hyperbaric oxygen. In contrast, these changes were followed by a return to nearly normal levels after 2 weeks of reloading when pre- and postconditioning were combined. Therefore, a combination of pre- and postconditioning with mild hyperbaric oxygen can be effective against the atrophy and decreased oxidative capacity of skeletal muscles associated with hindlimb unloading.

Enterococcus faecium strain R30 increases red blood cell velocity and prevents capillary regression in the soleus of hindlimb-unloaded rats via the eNOS/VEGF pathway.

OBJECTIVE: A chronic decrease in neuromuscular activity results in atrophy and capillary regression in skeletal muscles. The purposes of this study were to determine the effects of Enterococcus faecium strain R30 (R30) administration on (i) the hemodynamics of the rat soleus muscle, and (ii) the capillary regression normally associated with HU. METHODS: Experiment 1: The VRBC was measured for up to 1 hour after administration of R30 with or without the ß-blocker propranolol. Experiment 2: R30 was administered daily to control and HU rats for 2 weeks. Mean capillary luminal diameter, volume, and the levels of eNOS and VEGF protein were measured. RESULTS: Experiment 1: VRBC was faster 20, 40, and 60 minutes after than before the administration of R30: This effect was suppressed by propranolol administration. Experiment 2: R30 administration during HU increased capillary luminal diameter and volume and eNOS and VEGF protein levels in the soleus of HU rats. CONCLUSIONS: The results suggest that R30 increases VRBC in the soleus muscle via muscle sympathetic nerve activity (Experiment 1) and that R30 supplementation lessens the capillary regression normally associated with HU via the eNOS/VEGF pathway (Experiment 2).

Astaxanthin supplementation attenuates immobilization-induced skeletal muscle fibrosis via suppression of oxidative stress.

Immobilization induces skeletal muscle fibrosis characterized by increasing collagen synthesis in the perimysium and endomysium. Transforming growth factor-ß1 (TGF-ß1) is associated with this lesion via promoting differentiation of fibroblasts into myofibroblasts. In addition, reactive oxygen species (ROS) are shown to mediate TGF-ß1-induced fibrosis in tissues. These reports suggest the importance of ROS reduction for attenuating skeletal muscle fibrosis. Astaxanthin, a powerful antioxidant, has been shown to reduce ROS production in disused muscle. Therefore, we investigated the effects of astaxanthin supplementation on muscle fibrosis under immobilization. In the present study, immobilization increased the collagen fiber area, the expression levels of TGF-ß1, α-smooth muscle actin, and superoxide dismutase-1 protein and ROS production. However, these changes induced by immobilization were attenuated by astaxanthin supplementation. These results indicate the effectiveness of astaxanthin supplementation on skeletal muscle fibrosis induced by ankle joint immobilization.

Mild Hyperbaric Oxygen Inhibits Growth-related Decrease in Muscle Oxidative Capacity of Rats with Metabolic Syndrome.

AIM: We examined the effects of mild hyperbaric oxygen on the properties of the soleus muscle in rats with metabolic syndrome. METHODS: Five-week-old metabolic syndrome (SHR/NDmcr-cp, cp/cp) rats were divided into normobaric (CP) and mild hyperbaric oxygen (CP-H) groups (n=5/group). In addition, 5-week-old Wistar rats were assigned as the normobaric control (WR) group (n=5). The CP-H group was exposed to 1.25 atmospheres absolute with 36% oxygen for 3 h daily for 16 weeks. Succinate dehydrogenase (SDH) activity and mRNA levels of peroxisome proliferator-activated receptor γ coactivator-1α (Pgc-1α) in the soleus muscle were examined. The fiber type composition, cross-sectional areas, and SDH staining intensity in the soleus muscle were also examined. RESULTS: The CP-H group showed lower fasting and nonfasting blood glucose, glycated hemoglobin, total cholesterol, triglyceride, insulin, and systolic blood pressure levels; higher adiponectin levels; and higher SDH activity and mRNA levels of Pgc-1α in the muscle than the CP group. Compared with the CP group, the CP-H group had a lower percentage of type I fibers and observed type IIA fibers in the muscle. The CP-H group also had higher SDH staining intensity of type Ⅰ and type IIC fibers in the muscle than the CP group. No differences in these values were observed in the muscles of the WR and CP-H groups. CONCLUSION: Mild hyperbaric oxygen inhibited growth-related increase in blood glucose levels and decrease in muscle oxidative capacity of rats with metabolic syndrome because of improved oxidative metabolism.