Higher Muscle Tissue Oxygenation When Exposed to Hypobaric Hypoxia Than Normobaric Hypoxia

There has been recent debate on the potential difference in physiological response between exposure to simulated altitude (normobaric hypoxia) and terrestrial altitude (hypobaric hypoxia). Purpose: To determine the difference in the physiological response to normobaric and hypobaric hypoxia during exercise. Methods: Eight recreationally active subjects (27 ± 5 y old, 73.1 ± 7.4 kg body weight, 170.6 ± 6.7 cm height, and 19.3 ± 9.2 % body fat) completed incremental cycling exercise to volitional fatigue in three separate environments: normobaric normoxia (NN; 350 m), normobaric hypoxia (NH; simulated 3094 m), and hypobaric hypoxia (HH; 3094 m). Heart rate, blood oxygen saturation, and muscle tissue oxygenation were measured at rest and continuously throughout the exercise trials. Results: Blood oxygen saturation (SpO2) was ~10% higher in NN compared to the two hypoxic conditions (p \u3c 0.001) at rest and all exercise stages, with no difference between NH and HH (p \u3e 0.05). Heart rate was higher at rest in HH (98 ± 13 bpm) compared to NN (83 ± 15 bpm, p = 0.011) and NH (84 ± 14 bpm, p = 0.001) which persisted until 165 watts at which point no difference was observed (p \u3e 0.05). Muscle tissue oxygenation was 17% higher in HH compared to NN and 19% higher than NH throughout exposure (p \u3c 0.05). Conclusion: This data indicates that the hypoxic stress resulting from normobaric and hypobaric hypoxia are not the sameand that hypobaric hypoxia may not result in hypoxia at the level of the tissue

Substrate Use and Biochemical Response to a 3,211-km Bicycle Tour in Trained Cyclists

The purpose of this study was to assess the physiological adaptations in physically fit individuals to a period of intensified training. Ten trained males cycled outdoors ~170 km day−1 on 19 out of 21 days. Expired gas was collected on days 1 and 21 during maximal graded exercise and used for the determination of gross efficiency and whole body substrate use. Muscle biopsies were obtained before and after exercise on days 2 and 22 for the determination of mtDNA/gDNA ratio, gene expression, metabolic enzyme activity and glycogen use. Muscle glycogen before and after exercise, fat oxidation, and gross efficiency increased, carbohydrate oxidation decreased (p \u3c 0.05), and VO2max did not change over the 21 days of training. Citrate synthase (CS), β-hydroxyacyl CoA dehydrogenase (β-HAD) and cytochrome c oxidase (COX) enzyme activity did not change with training. CS and β-HAD mRNA did not change with acute exercise or training. COX (subunit IV) mRNA increased with acute exercise (p \u3c 0.05) but did not change over the 21 days. PGC-1α mRNA increased with acute exercise, but did not increase to the same degree on day 22 as it did on day 2 (p \u3c 0.05). UCP3 mRNA decreased with training (p \u3c 0.05). Acute exercise caused an increase in mitofusin2 (MFN2) mRNA (p \u3c 0.05) and a trend for an increase in mtDNA/gDNA ratio (p = 0.057). However, training did not affect MFN2 mRNA or mtDNA/gDNA ratio. In response to 3,211 km of cycling, changes in substrate use and gross efficiency appear to be more profound than mitochondrial adaptations in trained individuals

Metabolic Profile of the Ironman World Championships: A Case Study

Purpose: The purpose of this study was to determine the metabolic profile during the 2006 Ironman World Championship in Kailua-Kona, Hawaii. Methods: One recreational male triathlete completed the race in 10:40:16. Before the race, linear regression models were established from both laboratory and field measures to estimate energy expenditure and substrate utilization. The subject was provided with an oral dose of (2)H(2)(18)O approximately 64 h before the race to calculate total energy expenditure (TEE) and water turnover with the doubly labeled water (DLW) technique. Body weight, blood sodium and hematocrit, and muscle glycogen (via muscle biopsy) were analyzed pre- and postrace. Results: The TEE from DLW and indirect calorimetry was similar: 37.3 MJ (8,926 kcal) and 37.8 MJ (9,029 kcal), respectively. Total body water turnover was 16.6 L. and body weight decreased 5.9 kg. Hematocrit increased from 46 to 51% PCV. Muscle glycogen decreased from 152 to 48 mmoL/kg wet weight pre- to postrace. Conclusion: These data demonstrate the unique physiological demands of the Ironman World Championship and should be considered by athletes and coaches to prepare sufficient nutritional and hydration plans

Exercise-Induced Interleukin-6 and Metabolic Responses in Hot, Temperate, and Cold Conditions

The purpose of this study was to determine the effects of exercise in hot, cold, and temperate environments on plasma interleukin-6 (IL-6). Eleven recreationally trained males (age = 25 ± 4 years, height = 178 ± 5 cm, weight = 79.4 ± 13.5 kg, body fat = 14.7 ± 3.6%, VO2 peak = 54.6 ± 11.5 ml kg-1 min-1) performed a 1 hr cycling bout in hot (33 °C), cold (7 °C), and temperate (20 °C) environments at 60% of Wmax followed by 3 hr of supine recovery in temperate conditions. Expired gases were measured every 15 min during exercise and once every hour during recovery. Heart rate was continuously measured throughout the trials. Blood samples were obtained from the antecubital vein pre-exercise, immediately post-exercise, and 3 hr post-exercise. Blood samples were analyzed for plasma concentrations of IL-6 using a commercial ELISA kit. Plasma IL-6 concentrations were significantly higher immediately post-exercise (14.8 ± 1.6 pg ml-1, p = 0.008) and 3 hr post-exercise (14.8 ± 0.9 pg ml-1, p = 0.018) compared to pre-exercise (11.4 ± 2.4 pg ml-1), across all trials. There were no differences in plasma IL-6 concentrations (p = 0.207) between temperature conditions.Oxygen consumption and heart rate were higher and respiratory exchange ratio was lower in the hot compared to other conditions (p \u3c 0.05). These data indicate that the temperature in which exercise occurs does not affect acute plasma IL-6 response despite differences in metabolic state

Single muscle fiber adaptations to resistance training in men and women over 80 Y

The purpose of this study was to investigate whole muscle and single muscle fiber adaptations in old men (OM) and old women (OW) over 80 years of age in response to progressive resistance training (PRT). Six OM (82±1 y, 74±4 kg, BMI 25±1 kg•m-2) and six OW (85±1 y, 67±3 kg, BMI 27±1 kg•m-2) resistance trained the knee extensors (3 sets, 10 repetitions) at 70% one repetition maximum 3 d•wk-1 for 12 wks. Vastus lateralis muscle biopsies were obtained before and after the PRT program. Isolated muscle fibers were studied in vitro at 15°C for diameter (Dia), peak tension (Po), unloaded shortening velocity (Vo), and absolute peak power (Abs Pwr). With PRT, OM increased whole muscle strength (40±6%, p<0.05), with no change in whole muscle size. OW also increased whole muscle strength (26±6%, p<0.05) without a change in whole muscle size. No differences were observed in any of the single muscle fiber parameters among MHC I or MHC IIa muscle fibers from OM or OW. The novel finding of this study was that despite an increase in whole muscle strength there was no change in whole muscle size, single fiber diameter, or single fiber contractile function. Given that there was no change in muscle size or cellular function with PRT, the improvement in whole muscle strength point to neurological changes. These data suggest that the hypertrophic mechanisms that are typically apparent in humans with PRT are attenuated in individuals over 80 y.Thesis (Ph. D.)School of Physical Education, Sport, and Exercise Scienc

Skeletal Muscle mRNA Response to Hypobaric and Normobaric Hypoxia After Exercise

Environmental stimuli such as temperature and hypoxia can influence cellular signaling in the skeletal muscle. Previously we have reported no changes in gene expression related to mitochondrial development with acute exposure to normobaric hypoxia. However, exposure to hypobaric hypoxia may elicit different physiological responses. Purpose: To determine the effects of recovery in hypobaric hypoxia (HH), normobaric hypoxia (NH), and normobaric normoxia (NN) after exercise on gene expression related to mitochondrial biogenesis, myogenesis, and proteolysis. Methods: Recreationally trained participants (8 male, 7 female) each completed three trials of 1-h cycling at 70% of Wmax. Following exercise, participants sat in an environmentally controlled chamber for a 4-h recovery period in NN (975 m), NH (4,420 m), or HH (4,420 m) environmental conditions. Muscle biopsies were taken from the vastus lateralis pre-exercise and after a 4-h environmental exposure period. Samples were analyzed using qRT-PCR. Results: SpO2 was lower in HH than NH, which were both lower than in NN. Heart rate was higher in HH than NH, which were both higher than in NN. TFAM was unaltered in normobaric normoxia but increased after HH and NH exposure with no differences between HH and NH. MSTN decreased from pre- to post-exercise in all conditions and was lower in HH compared to NH and NN. Conclusion: Recovery in HH after exercise appears to have a greater effect on muscle oxygen transport than NH. Furthermore, MSTN tends to be further attenuated in HH than NH. Caution should be used when translating data obtained in a NH environment to a HH environment

Independent Effects of Hypoxia and Altitude on Human Physiology

PURPOSE: Decreased fraction of inspired oxygen (FiO2) is often used to simulate the atmospheric partial pressure of oxygen decreases experienced during high altitude sojourns. Therefore, we aimed to independently investigate hypoxia and altitude by isolating oxygen concentration and barometric pressure. METHODS: 18 subjects completed 3 trials (sea level, hypoxia, altitude). 90-minute duration and intensity matched hypoxic stimuli were induced via decreased FiO2 or 4,200 m ascent. Relative tissue oxygenation change and cardiovascular variables were measured during rest and a 3-minute step-test. RESULTS: Muscle oxygenated hemoglobin (O2Hb) and muscle deoxygenated hemoglobin (HHb) were not different across environments during rest or exercise (p\u3e0.339) with alterations noted during rest to exercise transitions (p2Hb at hypoxia and altitude were lower than sea level (p2Hb was lower at altitude than sea level (p=0.007) similarly trending compared to hypoxia (p=0.066). Exercising brain O2Hb was not different between hypoxia and sea level (p=0.158). Brain HHb at hypoxia and altitude were higher than sea level (p-1) and altitude (141±3 beats·min-1) were lower than sea level (127±44 beats·min- 1, p0.208). Exercise stroke volume at altitude (109.6±4.1 mL) was higher than hypoxia (97.8±3.3 mL) and sea level (99.8±3.9 mL, pCONCLUSIONS: During acute hypoxic stimuli, skeletal muscle maintains oxygenation while the brain does not. Tissue oxygenation may be mediated by environmentally driven cardiovascular compensation. FiO2 decreases may not satisfactorily simulate all physiological outcomes experienced during altitude induced barometric pressure decreases

Blood oxidative-stress markers during a high-altitude trek

Oxidative stress occurs as a result of altitude-induced hypobaric hypoxia and physical exercise. The effect of exercise on oxidative stress under hypobaric hypoxia is not well understood. To determine the effect of high-altitude exercise on blood oxidative stress. Nine male participants completed a 2-d trek up and down Mt Rainer, in North America, at a peak altitude of 4,393 m. Day 1 consisted of steady-pace climbing for 6.25 hr to a final elevation of 3,000 m. The 4,393-m summit was reached on Day 2 in approximately 5 hr. Climb-rest intervals varied but were consistent between participants, with approximately 14 hr of total time including rest periods. Blood samples were assayed for biomarkers of oxidative stress and antioxidant potential at the following time points: Pre (before the trek), 3Kup (at ascent to 3,000 m), 3Kdown (at 3,000 m on the descent), and Post (posttrek at base elevation). Blood serum variables included ferric-reducing antioxidant potential (FRAP), Trolox equivalent antioxidant capacity (TEAC), protein carbonyls (PC), and lipid hydroperoxides. Serum FRAP was elevated at 3Kup and 3Kdown compared with Pre and Post values (p = .004, 8% and 11% increase from Pre). Serum TEAC values were increased at 3Kdown and Post (p = .032, 10% and 18% increase from Pre). Serum PC were elevated at 3Kup and 3Kdown time points (p = .034, 194% and 138% increase from Pre), while lipid hydroperoxides were elevated Post only (p = .004, 257% increase from Pre). Findings indicate that high-altitude trekking is associated with increased blood oxidative stress