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  • 1.
    Björkman, Frida
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology, Björn Ekblom's and Mats Börjesson's research group.
    Edin, Fredrik
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology, Björn Ekblom's and Mats Börjesson's research group.
    Mattsson, C. Mikael
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology, Björn Ekblom's and Mats Börjesson's research group.
    Larsen, Filip
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology, Björn Ekblom's and Mats Börjesson's research group.
    Ekblom, Björn
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology, Björn Ekblom's and Mats Börjesson's research group.
    Regular oral moist snuff dipping does not impair physical performanceArticle in journal (Refereed)
  • 2. Boushel, Robert
    et al.
    Gnaiger, E
    Larsen, Filip J
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences.
    Helge, J W
    González-Alonso, J
    Ara, I
    Munch-Andersen, T
    van Hall, G
    Søndergaard, H
    Saltin, Bengt
    Calbet, J A L
    Maintained peak leg and pulmonary VO2 despite substantial reduction in muscle mitochondrial capacity.2015In: Scandinavian Journal of Medicine and Science in Sports, ISSN 0905-7188, E-ISSN 1600-0838, Vol. 25, no Suppl 4, p. 135-143Article in journal (Refereed)
    Abstract [en]

    We recently reported the circulatory and muscle oxidative capacities of the arm after prolonged low-intensity skiing in the arctic (Boushel et al., 2014). In the present study, leg VO2 was measured by the Fick method during leg cycling while muscle mitochondrial capacity was examined on a biopsy of the vastus lateralis in healthy volunteers (7 male, 2 female) before and after 42 days of skiing at 60% HR max. Peak pulmonary VO2 (3.52 ± 0.18 L.min(-1) pre vs 3.52 ± 0.19 post) and VO2 across the leg (2.8 ± 0.4L.min(-1) pre vs 3.0 ± 0.2 post) were unchanged after the ski journey. Peak leg O2 delivery (3.6 ± 0.2 L.min(-1) pre vs 3.8 ± 0.4 post), O2 extraction (82 ± 1% pre vs 83 ± 1 post), and muscle capillaries per mm(2) (576 ± 17 pre vs 612 ± 28 post) were also unchanged; however, leg muscle mitochondrial OXPHOS capacity was reduced (90 ± 3 pmol.sec(-1) .mg(-1) pre vs 70 ± 2 post, P < 0.05) as was citrate synthase activity (40 ± 3 μmol.min(-1) .g(-1) pre vs 34 ± 3 vs P < 0.05). These findings indicate that peak muscle VO2 can be sustained with a substantial reduction in mitochondrial OXPHOS capacity. This is achieved at a similar O2 delivery and a higher relative ADP-stimulated mitochondrial respiration at a higher mitochondrial p50. These findings support the concept that muscle mitochondrial respiration is submaximal at VO2max , and that mitochondrial volume can be downregulated by chronic energy demand.

  • 3.
    Cardinale, Daniele A.
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology.
    Larsen, Filip J
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology, Research group for Mitokondriell funktion och metabolisk kontroll.
    Jensen-Urstad, M
    Karolinska institutet.
    Rullman, E
    Karolinska institutet.
    Søndergaard, H
    Rigshospitalet, Köpenhamn, Danmark.
    Morales-Alamo, D
    University of Las Palmas de Gran Canaria, Spanien.
    Ekblom, Björn
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology, Björn Ekblom's research group.
    Calbet, J A L
    University of Las Palmas de Gran Canaria, Spanien.
    Boushel, Robert
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology. University of British Columbia, Vancouver, British Columbia, Canada.
    Muscle mass and inspired oxygen influence oxygen extraction at maximal exercise: role of mitochondrial oxygen affinity.2019In: Acta Physiologica, ISSN 1748-1708, E-ISSN 1748-1716, Vol. 225, no 1, article id e13110Article in journal (Refereed)
    Abstract [en]

    AIM:We examined the Fick components together with mitochondrial O2 affinity (p50mito ) in defining O2 extraction and O2 uptake during exercise with large and small muscle mass during normoxia (NORM) and hyperoxia (HYPER).

    METHODS:Seven individuals performed two incremental exercise tests to exhaustion on a bicycle ergometer (BIKE) and two on a one-legged knee extension ergometer (KE) in NORM or HYPER. Leg blood flow and VO2 were determined by thermodilution and the Fick method. Maximal ADP-stimulated mitochondrial respiration (OXPHOS) and p50mito were measured ex vivo in isolated mitochondria. Mitochondrial excess capacity in the leg was determined from OXPHOS in permeabilized fibers and muscle mass measured with magnetic resonance imaging in relation to peak leg O2 delivery.

    RESULTS:The ex vivo p50mito increased from 0.06±0.02 to 0.17±0.04 kPa with varying substrate supply and O2 flux rates from 9.84±2.91 to 16.34±4.07 pmol O2 ·s-1 ·μg-1 respectively. O2 extraction decreased from 83% in BIKE to 67% in KE as a function of a higher O2 delivery, and lower mitochondrial excess capacity. There was a significant relationship between O2 extraction and mitochondrial excess capacity and p50mito that was unrelated to blood flow and mean transit time.

    CONCLUSION:O2 extraction varies with mitochondrial respiration rate, p50mito and O2 delivery. Mitochondrial excess capacity maintains a low p50mito which enhances O2 diffusion from microvessels to mitochondria during exercise. This article is protected by copyright. All rights reserved.

  • 4.
    Cardinale, Daniele A.
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology.
    Larsen, Filip J
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology, Research group for Mitokondriell funktion och metabolisk kontroll.
    Lindholm, Peter
    Karolinska Institutet, Stockholm, Sweden..
    Ekblom, Björn
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology, Björn Ekblom's research group.
    Boushel, Robert
    Univ British Columbia, Vancouver, BC, Canada..
    Effects Of Hyperoxic-Supplemented High Intensity Interval Training On Endurance Performance, Maximal Oxygen Consumption And Mitochondrial Function In Trained Cyclists2019In: MEDICINE AND SCIENCE IN SPORTS AND EXERCISE Vol 51(2019):6. Supplement: S, Meeting Abstract: 1753, Lippincott Williams & Wilkins, 2019, Vol. 51, no 6, p. 463-464Conference paper (Other academic)
  • 5.
    Cardinale, Daniele A.
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology, Research group for Mitokondriell funktion och metabolisk kontroll.
    Larsen, Filip J
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology, Research group for Mitokondriell funktion och metabolisk kontroll.
    Lännerström, Johan
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences.
    Manselin, Tom
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences.
    Södergård, Olof
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences.
    Mijwel, Sara
    Karolinska institutet, Sweden.
    Lindholm, P
    Karolinska institutet, Sweden.
    Ekblom, Björn
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology, Björn Ekblom's research group.
    Boushel, Robert
    University of British Columbia, Vancouver, BC, Canada..
    Influence of Hyperoxic-Supplemented High-Intensity Interval Training on Hemotological and Muscle Mitochondrial Adaptations in Trained Cyclists.2019In: Frontiers in Physiology, ISSN 1664-042X, E-ISSN 1664-042X, Vol. 10, article id 730Article in journal (Refereed)
    Abstract [en]

    Background: Hyperoxia (HYPER) increases O2 carrying capacity resulting in a higher O2 delivery to the working muscles during exercise. Several lines of evidence indicate that lactate metabolism, power output, and endurance are improved by HYPER compared to normoxia (NORM). Since HYPER enables a higher exercise power output compared to NORM and considering the O2 delivery limitation at exercise intensities near to maximum, we hypothesized that hyperoxic-supplemented high-intensity interval training (HIIT) would upregulate muscle mitochondrial oxidative capacity and enhance endurance cycling performance compared to training in normoxia. Methods: 23 trained cyclists, age 35.3 ± 6.4 years, body mass 75.2 ± 9.6 kg, height 179.8 ± 7.9 m, and VO2max 4.5 ± 0.7 L min-1 performed 6 weeks polarized and periodized endurance training on a cycle ergometer consisting of supervised HIIT sessions 3 days/week and additional low-intensity training 2 days/week. Participants were randomly assigned to either HYPER (FIO2 0.30; n = 12) or NORM (FIO2 0.21; n = 11) breathing condition during HIIT. Mitochondrial respiration in permeabilized fibers and isolated mitochondria together with maximal and submaximal VO2, hematological parameters, and self-paced endurance cycling performance were tested pre- and posttraining intervention. Results: Hyperoxic training led to a small, non-significant change in performance compared to normoxic training (HYPER 6.0 ± 3.7%, NORM 2.4 ± 5.0%; p = 0.073, ES = 0.32). This small, beneficial effect on the self-paced endurance cycling performance was not explained by the change in VO2max (HYPER 1.1 ± 3.8%, NORM 0.0 ± 3.7%; p = 0.55, ES = 0.08), blood volume and hemoglobin mass, mitochondrial oxidative phosphorylation capacity (permeabilized fibers: HYPER 27.3 ± 46.0%, NORM 16.5 ± 49.1%; p = 0.37, ES = 3.24 and in isolated mitochondria: HYPER 26.1 ± 80.1%, NORM 15.9 ± 73.3%; p = 0.66, ES = 0.51), or markers of mitochondrial content which were similar between groups post intervention. Conclusions: This study showed that 6 weeks hyperoxic-supplemented HIIT led to marginal gain in cycle performance in already trained cyclists without change in VO2max, blood volume, hemoglobin mass, mitochondrial oxidative phosphorylation capacity, or exercise efficiency. The underlying mechanisms for the potentially meaningful performance effects of hyperoxia training remain unexplained and may raise ethical questions for elite sport.

  • 6.
    Cardinale, Daniele A.
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology, Research group for Mitokondriell funktion och metabolisk kontroll.
    Larsen, Filip J
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology, Research group for Mitokondriell funktion och metabolisk kontroll.
    Schiffer, Tomas A
    Karolinska Institute.
    Morales-Alamo, David
    University of Las Palmas de Gran Canaria.
    Ekblom, Björn
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology, Björn Ekblom's research group.
    Calbet, Jose A L
    University of Las Palmas de Gran Canaria.
    Holmberg, Hans-Christer
    Mid Sweden University, Östersund, The University of British Columbia, Vancouver, BC, Canada..
    Boushel, Robert
    The University of British Columbia, Vancouver, BC, Canada..
    Superior Intrinsic Mitochondrial Respiration in Women Than in Men.2018In: Frontiers in Physiology, ISSN 1664-042X, E-ISSN 1664-042X, Vol. 9, article id 1133Article in journal (Refereed)
    Abstract [en]

    Sexual dimorphism is apparent in humans, however, to date no studies have investigated mitochondrial function focusing on intrinsic mitochondrial respiration (i.e., mitochondrial respiration for a given amount of mitochondrial protein) and mitochondrial oxygen affinity (p50mito) in relation to biological sex in human. A skeletal muscle biopsy was donated by nine active women, and ten men matched for maximal oxygen consumption (VO2max) and by nine endurance trained men. Intrinsic mitochondrial respiration, assessed in isolated mitochondria, was higher in women compared to men when activating complex I (CIP) and complex I+II (CI+IIP) (p < 0.05), and was similar to trained men (CIP, p = 0.053; CI+IIP, p = 0.066). Proton leak and p50mito were higher in women compared to men independent of VO2max. In conclusion, significant novel differences in mitochondrial oxidative function, intrinsic mitochondrial respiration and p50mito exist between women and men. These findings may represent an adaptation in the oxygen cascade in women to optimize muscle oxygen uptake to compensate for a lower oxygen delivery during exercise.

  • 7.
    Carlström, Mattias
    et al.
    Karolinska Institutet.
    Larsen, Filip J
    Karolinska Institutet.
    Nyström, Thomas
    Hezel, Michael
    Borniquel, Sara
    Weitzberg, Eddie
    Lundberg, Jon O
    Dietary inorganic nitrate reverses features of metabolic syndrome in endothelial nitric oxide synthase-deficient mice.2010In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 107, no 41, p. 17716-20Article in journal (Refereed)
    Abstract [en]

    The metabolic syndrome is a clustering of risk factors of metabolic origin that increase the risk for cardiovascular disease and type 2 diabetes. A proposed central event in metabolic syndrome is a decrease in the amount of bioavailable nitric oxide (NO) from endothelial NO synthase (eNOS). Recently, an alternative pathway for NO formation in mammals was described where inorganic nitrate, a supposedly inert NO oxidation product and unwanted dietary constituent, is serially reduced to nitrite and then NO and other bioactive nitrogen oxides. Here we show that several features of metabolic syndrome that develop in eNOS-deficient mice can be reversed by dietary supplementation with sodium nitrate, in amounts similar to those derived from eNOS under normal conditions. In humans, this dose corresponds to a rich intake of vegetables, the dominant dietary nitrate source. Nitrate administration increased tissue and plasma levels of bioactive nitrogen oxides. Moreover, chronic nitrate treatment reduced visceral fat accumulation and circulating levels of triglycerides and reversed the prediabetic phenotype in these animals. In rats, chronic nitrate treatment reduced blood pressure and this effect was also present during NOS inhibition. Our results show that dietary nitrate fuels a nitrate-nitrite-NO pathway that can partly compensate for disturbances in endogenous NO generation from eNOS. These findings may have implications for novel nutrition-based preventive and therapeutic strategies against cardiovascular disease and type 2 diabetes.

  • 8.
    Larsen, Filip
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Björn Ekblom's research group.
    Ekblom, Björn
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Björn Ekblom's research group.
    Effects of dietary nitrate on oxygen cost during exercise2007In: Acta Physiologica, ISSN 1748-1708, E-ISSN 1748-1716, Vol. 191, no 1, p. 59-66Article in journal (Refereed)
    Abstract [en]

    AIM: Nitric oxide (NO), synthesized from l-arginine by NO synthases, plays a role in adaptation to physical exercise by modulating blood flow, muscular contraction and glucose uptake and in the control of cellular respiration. Recent studies show that NO can be formed in vivo also from the reduction of inorganic nitrate (NO(3) (-)) and nitrite (NO(2) (-)). The diet constitutes a major source of nitrate, and vegetables are particularly rich in this anion. The aim of this study was to investigate if dietary nitrate had any effect on metabolic and circulatory parameters during exercise. METHOD: In a randomized double-blind placebo-controlled crossover study, we tested the effect of dietary nitrate on physiological and metabolic parameters during exercise. Nine healthy young well-trained men performed submaximal and maximal work tests on a cycle ergometer after two separate 3-day periods of dietary supplementation with sodium nitrate (0.1 mmol kg(-1) day-1) or an equal amount of sodium chloride (placebo). RESULTS: The oxygen cost at submaximal exercise was reduced after nitrate supplementation compared with placebo. On an average Vo(2) decreased from 2.98 +/- 0.57 during CON to 2.82 +/- 0.58 L min(-1) during NIT (P < 0.02) over the four lowest submaximal work rates. Gross efficiency increased from 19.7 +/- 1.6 during CON to 21.1 +/- 1.3% during NIT (P < 0.01) over the four lowest work rates. There was no difference in heart rate, lactate [Hla], ventilation (VE), VE/Vo(2) or respiratory exchange ratio between nitrate and placebo during any of the submaximal work rates. CONCLUSION: We conclude that dietary nitrate supplementation, in an amount achievable through a diet rich in vegetables, results in a lower oxygen demand during submaximal work. This highly surprising effect occurred without an accompanying increase in lactate concentration, indicating that the energy production had become more efficient. The mechanism of action needs to be clarified but a likely first step is the in vivo reduction of dietary nitrate into bioactive nitrogen oxides including nitrite and NO.

  • 9.
    Larsen, Filip
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Björn Ekblom's research group.
    Ekblom, Björn
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Björn Ekblom's research group.
    The low intracellular oxygen tension during exercise is a function of limited oxygen supply and high mitochondrial oxygen affinity: A letter to the editor2012In: European Journal of Applied Physiology, ISSN 1439-6319, E-ISSN 1439-6327, Vol. 112, no 11, p. 3935-3936Article in journal (Other academic)
    Abstract [en]

    A letter to the editor is presented in response to an article on muscle intracellular oxygenation during exercise published in a previous issue of the journal.

  • 10.
    Larsen, Filip
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Björn Ekblom's research group.
    Ekblom, Björn
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Björn Ekblom's research group.
    Sahlin, Kent
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Research group for Mitokondriell funktion och metabolisk kontroll.
    Mitochondrial oxygen affinity predicts basal metabolic rate in humans2011In: The FASEB Journal, ISSN 0892-6638, E-ISSN 1530-6860, Vol. 25, no 8, p. 2843-52Article in journal (Refereed)
    Abstract [en]

    The basal metabolic rate (BMR) is referred to as the minimal rate of metabolism required to support basic body functions. It is well known that individual BMR varies greatly, even when correcting for body weight, fat content, and thyroid hormone levels, but the mechanistic determinants of this phenomenon remain unknown. Here, we show in humans that mass-related BMR correlates strongly to the mitochondrial oxygen affinity (p50(mito); R(2)=0.66, P=0.0004) measured in isolated skeletal muscle mitochondria. A similar relationship was found for oxygen affinity and efficiency during constant-load submaximal exercise (R(2)=0.46, P=0.007). In contrast, BMR did not correlate to overall mitochondrial density or to proton leak. Mechanistically, part of the p50(mito) seems to be controlled by the excess of cytochrome c oxidase (COX) protein and activity relative to other mitochondrial proteins. This is illustrated by the 5-fold increase in p50(mito) after partial cyanide inhibition of COX at doses that do not affect maximal mitochondrial electron flux through the ETS. These data suggest that the interindividual variation in BMR in humans is primarily explained by differences in mitochondrial oxygen affinity. The implications of these findings are discussed in terms of a trade-off between aerobic efficiency and power.

  • 11.
    Larsen, Filip
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Björn Ekblom's research group.
    Ekblom, Björn
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Björn Ekblom's research group.
    Sahlin, Kent
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences.
    Weitzberg, Eddie
    Lundberg, Jon
    Effects of dietary nitrate on blood pressure in healthy volunteers2006In: New England Journal of Medicine, ISSN 0028-4793, E-ISSN 1533-4406, Vol. 28, no 355(26), p. 2792-3Article in journal (Refereed)
    Abstract [en]

    To the Editor:

    Nitric oxide, generated by nitric oxide synthase, is a key regulator of vascular integrity. This system is dysfunctional in many cardiovascular disorders, including hypertension. A fundamentally different pathway for the generation of nitric oxide was recently described in which the anions nitrate (NO3 ) and nitrite (NO2 ) are converted into nitric oxide and other bioactive nitrogen oxides.1-3 Nitrate is abundant in our diet, and particularly high levels are found in many vegetables.3

    We examined the effect of 3-day dietary supplementation with either sodium nitrate (at a dose of 0.1 mmol per kilogram of body weight per day) or placebo (sodium chloride, at a dose of 0.1 mmol per kilogram per day) on blood pressure in 17 physically active, healthy volunteers, none of whom smoked (15 men and 2 women; mean age, 24 years). The study had a randomized, double-blind, crossover design with two different treatment periods during which the subjects received either nitrate or placebo; the treatment periods were separated by a washout period of at least 10 days. The compounds were dissolved in water and could not be distinguished by taste or appearance. During the two treatment periods, the subjects were instructed to avoid all foods with a moderate or high nitrate content.3

    Systolic blood pressure Effects of 3-Day Dietary Supplementation with Inorganic Nitrate or Placebo on Systolic (Panel A) and Diastolic (Panel B) Blood Pressure in 17 Healthy Volunteers.) and pulse rate did not change significantly after nitrate supplementation, as compared with placebo supplementation. However, the diastolic blood pressure was on average 3.7 mm Hg lower after nitrate supplementation than after placebo supplementation (P<0.02) (Figure 1B), and the mean arterial pressure was 3.2 mm Hg lower (P<0.03). Plasma nitrate levels were higher after nitrate ingestion than after placebo ingestion (mean [±SD], 178±51 and 26±11 μM, respectively; P<0.001), as were plasma nitrite levels (219±105 and 138±38 nM, respectively; P<0.01).

    The daily nitrate dose used in the study corresponds to the amount normally found in 150 to 250 g of a nitrate-rich vegetable such as spinach, beetroot, or lettuce. It is clear from earlier studies, such as the Dietary Approaches to Stop Hypertension (DASH) trial, that a diet rich in fruits and vegetables can reduce blood pressure,4,5 but attempts to modify single nutrients have been inconsistent. Therefore, it has been argued that the effect of any individual nutrient is too small to detect in trials. In our study, reduced blood pressure was associated with nitrate supplementation alone; this effect was evident in young normotensive subjects. In fact, it was similar to that seen in the healthy control group in the DASH study.4 The exact mechanism behind the blood-pressure–lowering effect of nitrate needs to be clarified in future studies.

    We conclude that short-term dietary supplementation with inorganic nitrate reduces diastolic blood pressure in healthy young volunteers.

  • 12.
    Larsen, Filip J.
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences.
    Dietary inorganic nitrate: role in exercise physiology, cardiovascular and metabolic regulation2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Nitric oxide (NO) is a ubiquitous signaling molecule with a vast number of tasks in the body, including regulation of cardiovascular and metabolic function. A decreased bioavailability of NO is a central event in disorders such as hypertension and metabolic syndrome. NO is also important in the regulation of blood flow and metabolism during exercise. The production of NO has previously been thought to be under the exclusive control of the nitric oxide synthases (NOS) but this view is now being seriously challenged. Recent lines of research suggest the existence of an NO-synthase independent pathway in which the supposedly inert NO oxidation products nitrate (NO3-) and nitrite (NO2-) can be reduced back to NO in blood and tissues. An important additional source of nitrate is our everyday diet and certain vegetables are particularly rich in this anion. In this thesis the possibility that dietary derived nitrate is metabolized in vivo to form reactive nitrogen oxides with NO-like bioactivity has been explored. It is shown that nitrate in amounts easily achieved via the diet, increases the systemic levels of nitrite and reduces blood pressure in healthy humans. Moreover, nitrate reduces whole body oxygen cost during submaximal and maximal exercise; a surprising effect involving improvement in mitochondrial efficiency and reduced expression of specific mitochondrial proteins regulating proton conductance. Alterations in the mitochondrial affinity for oxygen can explain this reduction in both submaximal and maximal oxygen consumption and predicts basal metabolic rate in humans. Finally, in mice lacking endothelial NO synthase, dietary supplementation with nitrate could reverse several features of the metabolic syndrome that develop in these animals. These studies demonstrate that dietary nitrate can fuel a nitrate-nitrite-NO pathway with important implications for cardiovascular and metabolic functions in health and disease.

  • 13.
    Larsen, Filip J
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Björn Ekblom's research group.
    Anderson, Martin
    Ekblom, Björn
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Björn Ekblom's research group.
    Nyström, Thomas
    Cardiorespiratory fitness predicts insulin action and secretion in healthy individuals.2012In: Metabolism: Clinical and Experimental, ISSN 0026-0495, E-ISSN 1532-8600, Vol. 61, no 1, p. 12-6Article in journal (Refereed)
    Abstract [en]

    Long-term cardiorespiratory fitness (CRF) and the development of type 2 diabetes mellitus are inversely correlated. Here, we examined the relationships between peak oxygen uptake (VO(2)peak), on the one hand, and glucose infusion rate at rest (GIR(rest)) and during exercise (GIR(exercise)), as well as insulin secretion (both the early and late phases of response [area under the curve {AUC}(insulin)]), on the other. Eight male and 4 female healthy, lean, nonsmoking volunteers were recruited. The VO(2)peak was measured during graded exercise on a cycle ergometer until exhaustion was reached. The GIR(rest) and GIR(exercise) were determined using a euglycemic-hyperinsulinemic clamp, and insulin secretion at rest was evaluated with an intravenous glucose tolerance test. The VO(2)peak correlated positively to GIR(rest) (r = 0.81, P = .001) and GIR(exercise) (r = 0.87, P < .001) and negatively to AUC(insulin) (r = -0.64, P = .03). The respiratory exchange ratio (RER) during insulin infusion was positively correlated to GIR(rest) (r = 0.83, P < .001) and GIR(exercise) (r = 0.86, P < .01) and negatively correlated to both the early insulin response (r = -0.86, P < .0001) and AUC(insulin) (r = -0.87, P = .001). The VO(2)peak accounted for 45% of the variability in RER (R(2) = 0.45, P = .035). In this healthy population, CRF and RER were highly correlated to insulin sensitivity and secretion, as well as to the ability to alter the substrate being oxidized during exercise. These findings highlight the importance of good CRF to maintaining normal insulin action.

  • 14.
    Larsen, Filip J
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology, Björn Ekblom's and Mats Börjesson's research group.
    Schiffer, Tomas A
    Ekblom, Björn
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology, Björn Ekblom's and Mats Börjesson's research group.
    Mattsson, Mathias P
    Checa, Antonio
    Wheelock, Craig E
    Nyström, Thomas
    Lundberg, Jon O
    Weitzberg, Eddie
    Dietary nitrate reduces resting metabolic rate: a randomized, crossover study in humans.2014In: American Journal of Clinical Nutrition, ISSN 0002-9165, E-ISSN 1938-3207, Vol. 99, no 4, p. 843-50Article in journal (Refereed)
    Abstract [en]

    BACKGROUND: Nitrate, which is an inorganic anion abundant in vegetables, increases the efficiency of isolated human mitochondria. Such an effect might be reflected in changes in the resting metabolic rate (RMR) and formation of reactive oxygen species. The bioactivation of nitrate involves its active accumulation in saliva followed by a sequential reduction to nitrite, nitric oxide, and other reactive nitrogen species.

    OBJECTIVE: We studied effects of inorganic nitrate, in amounts that represented a diet rich in vegetables, on the RMR in healthy volunteers.

    DESIGN: In a randomized, double-blind, crossover study, we measured the RMR by using indirect calorimetry in 13 healthy volunteers after a 3-d dietary intervention with sodium nitrate (NaNO3) or a placebo (NaCl). The nitrate dose (0.1 mmol · kg(-1) · d(-1)) corresponded to the amount in 200-300 g spinach, beetroot, lettuce, or other vegetable that was rich in nitrate. Effects of direct nitrite exposure on cell respiration were studied in cultured human primary myotubes.

    RESULTS: The RMR was 4.2% lower after nitrate compared with placebo administration, and the change correlated strongly to the degree of nitrate accumulation in saliva (r(2) = 0.71). The thyroid hormone status, insulin sensitivity, glucose uptake, plasma concentration of isoprostanes, and total antioxidant capacity were unaffected by nitrate. The administration of nitrite to human primary myotubes acutely inhibited respiration.

    CONCLUSIONS: Dietary inorganic nitrate reduces the RMR. This effect may have implications for the regulation of metabolic function in health and disease.

  • 15.
    Larsen, Filip J
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology, Research group for Mitokondriell funktion och metabolisk kontroll.
    Schiffer, Tomas A
    Ørtenblad, Niels
    Zinner, Christoph
    Morales-Alamo, David
    Willis, Sarah J
    Calbet, Jose A
    Holmberg, Hans-Christer
    Boushel, Robert
    High-intensity sprint training inhibits mitochondrial respiration through aconitase inactivation.2016In: The FASEB Journal, ISSN 0892-6638, E-ISSN 1530-6860, Vol. 30, no 1, p. 417-427Article in journal (Refereed)
    Abstract [en]

    Intense exercise training is a powerful stimulus that activates mitochondrial biogenesis pathways and thus increases mitochondrial density and oxidative capacity. Moderate levels of reactive oxygen species (ROS) during exercise are considered vital in the adaptive response, but high ROS production is a serious threat to cellular homeostasis. Although biochemical markers of the transition from adaptive to maladaptive ROS stress are lacking, it is likely mediated by redox sensitive enzymes involved in oxidative metabolism. One potential enzyme mediating such redox sensitivity is the citric acid cycle enzyme aconitase. In this study, we examined biopsy specimens of vastus lateralis and triceps brachii in healthy volunteers, together with primary human myotubes. An intense exercise regimen inactivated aconitase by 55-72%, resulting in inhibition of mitochondrial respiration by 50-65%. In the vastus, the mitochondrial dysfunction was compensated for by a 15-72% increase in mitochondrial proteins, whereas H2O2 emission was unchanged. In parallel with the inactivation of aconitase, the intermediary metabolite citrate accumulated and played an integral part in cellular protection against oxidative stress. In contrast, the triceps failed to increase mitochondrial density, and citrate did not accumulate. Instead, mitochondrial H2O2 emission was decreased to 40% of the pretraining levels, together with a 6-fold increase in protein abundance of catalase. In this study, a novel mitochondrial stress response was highlighted where accumulation of citrate acted to preserve the redox status of the cell during periods of intense exercise.-Larsen, F. J., Schiffer, T. A., Ørtenblad, N., Zinner, C., Morales-Alamo, D., Willis, S. J., Calbet, J. A., Holmberg, H.-C., Boushel, R. High-intensity sprint training inhibits mitochondrial respiration through aconitase inactivation.

  • 16.
    Larsen, Filip J
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Björn Ekblom's research group.
    Weitzberg, Eddie
    Lundberg, Jon O
    Ekblom, Björn
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Björn Ekblom's research group.
    Dietary nitrate reduces maximal oxygen consumption while maintaining work performance in maximal exercise.2010In: Free Radical Biology & Medicine, ISSN 0891-5849, E-ISSN 1873-4596, Vol. 48, no 2, p. 342-7Article in journal (Refereed)
    Abstract [en]

    The anion nitrate-abundant in our diet-has recently emerged as a major pool of nitric oxide (NO) synthase-independent NO production. Nitrate is reduced stepwise in vivo to nitrite and then NO and possibly other bioactive nitrogen oxides. This reductive pathway is enhanced during low oxygen tension and acidosis. A recent study shows a reduction in oxygen consumption during submaximal exercise attributable to dietary nitrate. We went on to study the effects of dietary nitrate on various physiological and biochemical parameters during maximal exercise. Nine healthy, nonsmoking volunteers (age 30+/-2.3 years, VO(2max) 3.72+/-0.33 L/min) participated in this study, which had a randomized, double-blind crossover design. Subjects received dietary supplementation with sodium nitrate (0.1 mmol/kg/day) or placebo (NaCl) for 2 days before the test. This dose corresponds to the amount found in 100-300 g of a nitrate-rich vegetable such as spinach or beetroot. The maximal exercise tests consisted of an incremental exercise to exhaustion with combined arm and leg cranking on two separate ergometers. Dietary nitrate reduced VO(2max) from 3.72+/-0.33 to 3.62+/-0.31 L/min, P<0.05. Despite the reduction in VO(2max) the time to exhaustion trended to an increase after nitrate supplementation (524+/-31 vs 563+/-30 s, P=0.13). There was a correlation between the change in time to exhaustion and the change in VO(2max) (R(2)=0.47, P=0.04). A moderate dietary dose of nitrate significantly reduces VO(2max) during maximal exercise using a large active muscle mass. This reduction occurred with a trend toward increased time to exhaustion implying that two separate mechanisms are involved: one that reduces VO(2max) and another that improves the energetic function of the working muscles.

  • 17.
    Larsen, Filip
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Björn Ekblom's research group.
    Schiffer, TA
    Borniquel, S
    Sahlin, Kent
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Research group for Mitokondriell funktion och metabolisk kontroll.
    Ekblom, Björn
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Björn Ekblom's research group.
    Lundberg, JO
    Weitzberg, E
    Dietary inorganic nitrate improves mitochondrial efficiency in humans.2011In: Cell Metabolism, ISSN 1550-4131, Vol. 13, no 2, p. 149-159Article in journal (Refereed)
    Abstract [en]

    Nitrate, an inorganic anion abundant in vegetables, is converted in vivo to bioactive nitrogen oxides including NO. We recently demonstrated that dietary nitrate reduces oxygen cost during physical exercise, but the mechanism remains unknown. In a double-blind crossover trial we studied the effects of a dietary intervention with inorganic nitrate on basal mitochondrial function and whole-body oxygen consumption in healthy volunteers. Skeletal muscle mitochondria harvested after nitrate supplementation displayed an improvement in oxidative phosphorylation efficiency (P/O ratio) and a decrease in state 4 respiration with and without atractyloside and respiration without adenylates. The improved mitochondrial P/O ratio correlated to the reduction in oxygen cost during exercise. Mechanistically, nitrate reduced the expression of ATP/ADP translocase, a protein involved in proton conductance. We conclude that dietary nitrate has profound effects on basal mitochondrial function. These findings may have implications for exercise physiology- and lifestyle-related disorders that involve dysfunctional mitochondria.

  • 18.
    Manselin, Tom A
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology.
    Södergård, Olof
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology.
    Larsen, Filip J
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology, Research group for Mitokondriell funktion och metabolisk kontroll.
    Lindholm, Peter
    Karolinska institutet.
    Aerobic efficiency is associated with the improvement in maximal power output during acute hyperoxia.2017In: Physiological Reports, E-ISSN 2051-817X, Vol. 5, no 2, article id e13119Article in journal (Refereed)
    Abstract [en]

    This study investigated the relationship between aerobic efficiency during cycling exercise and the increase in physical performance with acute hyperoxic exposure (FiO2 ~31%) (HOX) and also tested the hypothesis that fat oxidation could be increased by acute hyperoxia. Fourteen males and four females were recruited for two sessions, where they exercised for 2 × 10 min at 100 W to determine efficiency. HOX and normoxia (NOX) were administered randomly on both occasions to account for differences in nitrogen exchange. Thereafter, a progressive ramp test was performed to determine VO2max and maximal power output (Wmax). After 30 min rest, workload was set to 80% of maximal power output (Wmax) for a time to exhaustion test (TTE). At 100W gross efficiency was reduced from 19.4% during NOX to 18.9% during HOX (P ≤ 0.0001). HOX increased fat oxidation at 100 W by 52% from 3.41 kcal min(-1) to 5.17 kcal min(-1) (P ≤ 0.0001) with a corresponding reduction in carbohydrate oxidation. Wmax increased by 2.4% from 388.8 (±82.1) during NOX to 397.8 (±83.5) during HOX (P ≤ 0.0001). SaO2 was higher in HOX both at the end of the maximal exercise test and TTE. Subjects with a high level of efficiency in NOX had a larger improvement in Wmax with HOX, in agreement with the hypothesis that an optimum level of efficiency exists that maximizes power production. No association between mitochondrial excess capacity and endurance performance was found; increases in oxygen supply seemed to increase maximal aerobic power production and maintain/increase endurance capacity at the same relative workload.

  • 19.
    Mattsson, C. Mikael
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences.
    Björkman, Frida
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Björn Ekblom's research group.
    Edin, Fredrik
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Björn Ekblom's research group.
    Larsen, Filip
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Björn Ekblom's research group.
    Ekblom, Björn
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Björn Ekblom's research group.
    Regular moist snuff dipping does not affect endurance exercise performance2013Conference paper (Refereed)
    Abstract [en]

    Physiological and medical effects of snuff have previously been obtained either in cross-sectional studies or after snuff administration to non-tobacco users, but the effects of snuff cessation (SC) after several years of daily use on individual level are unknown. 24 participants with >2 years of daily snuff-use were tested before and after >6 weeks SC (SCG), together with a control group (CO) of 11 snuff users who kept their normal habits. Resting heart rate (HR) was significantly lower in SCG after SC. Body mass in SCG group increased by 1.4 ± 1.7 kg and blood pressure (BP) were reduced, but without significant differences between groups. Total cholesterol increased from 4.12 ± 0.54 (95% CI 3.89–4.35) to 4.46 ± 0.70 (95% CI 4.16–4.75) mM/L in SCG, due to increased LDL, and this change was significantly different from CO. Resting values of HDL, C-reactive protein, and free fatty acids (FFA) remained unchanged in both groups. During a four-stage incremental (from 50 to 80% of VO2max) and a prolonged (60 min at 50% of VO2max) cycling test HR and BP were reduced in SCG, while oxygen uptake (VO2), respiratory exchange ratio, blood lactate (bLa) and blood glucose (bGlu) concentration, and rate of perceived exertion were unchanged. All measurements were unchanged in CO. During the prolonged exercise FFA was reduced but there was no significant difference between groups. During the maximal treadmill running test peak values of VO2, pulmonary ventilation (VE), time to exhaustion and bLa were unchanged in both groups. In conclusion, endurance exercise performance (VO2max and maximal endurance time) does not seem to be affected by prolonged snuff use, while effects on cardiovascular risk factors are contradictory.

  • 20.
    Mattsson, C. Mikael
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences.
    Larsen, Filip
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology, Björn Ekblom's and Mats Börjesson's research group.
    Kondition och uthållighet: För träning, tävling och hälsa2013Book (Other (popular science, discussion, etc.))
    Abstract [sv]

    Vilken intervallform är den mest effektiva i syfte att förbättra konditionen? Är det viktigt att ett träningsupplägg styrs av individualisering? Vilka positiva hälsoeffekter medför en förbättrad kondition? Och vad händer i framtiden – kommer drömgränsen under två timmar på maraton, att sprängas?

    En sammanställning och tolkning av den kunskap vi i nuläget har om fysiologi och träningslära.

    Boken Kondition och uthållighet är en sammanställning och tolkning av den kunskap vi i nuläget har om fysiologi och träningslära. Den beskriver en mängd faktorer och situationer kopplade till träning, prestation, utveckling och hälsa. Den vägleder dig som planerar och genomför träningen - aktiv eller tränare – att välja rätt träningsupplägg med hänsyn till träningsgrad och ambitionsnivå.

    Hälsoeffekter och ofattbara prestationer

    Att träna sin kondition medför en lång rad positiva hälsoeffekter såsom ökad livslängd, förbättrad livskvalitet och minskad risk för en mängd sjukdomar. Vid ökad träningsdos genomgår kroppen en rad förändringar för att anpassa sig till de krav som belastningen kräver. Kroppen är lyckligtvis enormt anpassningsbar och får den bara tillräckligt mycket träning kan den lära sig att tåla stora påfrestningar. Detta bidrar till att idrottare som specialiserar sig, och tränar mycket under lång tid, kan uppnå häpnadsväckande prestationer. Ju sämre kondition och uthållighet du har, desto mindre krävs för att du ska förbättra dig. Ju bättre kondition och uthållighet du har, desto hårdare belastning krävs för att du ska förbättra dig ytterligare.

    Pulsträning

    Ett sätt att mäta träningsbelastning är att använda puls och pulsklocka. Författarna, som även har skrivit träningshäftet Pulsträning (SISU Idrottsböcker 2011), förordar en indelning med sex intensitetszoner som baseras på beräkningar av individuella värden på vilo-, tröskel- och maxpuls. Beroende på hur vältränad man är kommer de olika zonerna att hamna mellan olika pulsnivåer. I den här boken beskrivs vad som tränas i de olika zonerna och varför man utför denna träning, samt hur man ska fördela träningsmängden mellan de olika zonerna.

    Intervallträning och individualisering

    Intervallträning innebär att man delar upp ett träningspass i mindre bitar med viloperioder i mellan, vilket möjliggör att hårda träningspass kan genomföras med en större mängd arbete på hög intensitet. Forskning tyder på att högintensiv intervallträning behövs för att man ska få ut så mycket som möjligt av sin konditionsträning. Vid intervallträning är det extra tydligt att man för bästa effekt bör utgå från sin egen förmåga; att man strävar efter en relativ belastning och upplevelse av trötthet, under och efter intervallpassen.

    Bokens upplägg

    Bokens första del går igenom grunderna i fysiologi och den andra delen handlar om vad som händer och vad man behöver tänka på vid planering, utförande och utvärdering av träning och tävling i konditions- och uthållighetsidrotter. Kondition och uthållighet tar också upp områden som återhämtning, skador, olika riskfaktorer och näringslära, vilka har en direkt betydelse för konditionsträning, oavsett om det handlar om att vinna OS eller träning för hälsa och ett långt aktivt liv.

  • 21.
    Mattsson, C. Mikael
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology, Björn Ekblom's and Mats Börjesson's research group.
    Larsen, Filip
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology, Björn Ekblom's and Mats Börjesson's research group.
    Pulsträning2011Book (Other (popular science, discussion, etc.))
    Abstract [sv]

    Att träna pulsbaserat skapar perfekta förutsättningarna för en positiv utveckling av din kondition eftersom du tränar utifrån din egen förmåga. Pulsen hjälper dig att träna på rätt nivå på de enskilda träningspassen och kan användas vid all form av konditionsträning. I häftet Pulsträning lär du dig grunderna för att träna med puls och hur du genom att använda olika belastningar kan uppnå olika effekter av din träning.  Du får också förslag på olika tester som både hjälper dig att träna effektivare och skapar motivation.

  • 22.
    Mattsson, C. Mikael
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology.
    Larsen, Filip
    Karolinska insitutet.
    Holmberg, Hans Christer
    Mittuniversitetet.
    Den nödvändiga distansträningen2014In: Svensk Idrottsforskning: Organ för Centrum för Idrottsforskning, ISSN 1103-4629, Vol. 23, no 3, p. 8-13Article in journal (Other academic)
    Abstract [sv]

    Korta och intensiva intervallpass är ett trendigt sätt att förbättra sin kondition. Men för att bli en bra löpare, längdåkare eller cyklist måste man träna många långa pass i ett lägre tempo. Forskning har visat att högintensiv intervallträning är tidseffektiv och ger bra effekt på många parametrar som är viktiga för konditionsidrottare. Tanken att ersätta nötandet i spåret med kort och snabb träning kan därför låta lockande. Men fullt så enkelt är det inte. Idrottsfysiologerna Mikael Mattsson, Filip Larsen och H-C Holmberg har studerat den forskning som finns om distansträning. Den visar att det inte går att komma runt den lågintensiva träningen om man vill bli en riktigt bra löpare, orienterare, längdskidåkare eller cyklist. På maraton finns till exempel ett nästan linjärt förhållande mellan träningsmängd och prestation. Ju fler mil löparen tränar i veckan desto bättre blir tiden. Kanske räcker det med att studera hur eliten tränar för att förstå distansträningens betydelse. Visserligen är den intensiva intervallträningen viktig även för dem, särskilt inför viktiga tävlingar. Men upp till 90 procent av den totala träningstiden eller minst 3-4 timmar per dag ägnar de åt mer lågintensiva pass.

  • 23.
    Mattsson, C. Mikael
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Björn Ekblom's research group.
    Ståhlberg, Marcus
    Institutionen för Medicin, Enheten för kardiologi, Karolinska Universitetssjukhuset.
    Larsen, Filip
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Björn Ekblom's research group.
    Braunschweig, Frieder
    Institutionen för Medicin, Enheten för kardiologi, Karolinska Universitetssjukhuset.
    Ekblom, Björn
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Björn Ekblom's research group.
    Late cardiovascular drift observable during ultra endurance exercise.2011In: Medicine & Science in Sports & Exercise, ISSN 0195-9131, E-ISSN 1530-0315, Vol. 43, no 7, p. 1162-1168Article in journal (Refereed)
    Abstract [en]

    Introduction: The present study investigates the adaptation of the central circulation to ultraenduranceexercise, including the relative contributions of changes in stroke volume (SV) andarterio-venous oxygen difference (a-v O2 diff) to the increased oxygen pulse (VO2/HR).Methods: We evaluated subjects undergoing 12h of mixed exercise at controlled intensity(n=8) and a 53h Adventure race (n=20). Heart rate (HR), oxygen uptake (VO2), and cardiacoutput determined using non-invasive gas rebreathing (CORB) were measured during cyclingat fixed work rate after 0, 4, 8, 12 hours, and 0, 20, and 53 hours of continuous exercise in the12 and 53 h protocol, respectively.Results and Conclusion: The central circulation changed in several steps in response to ultraenduranceexercise. Compared to initial levels, VO2 was increased at every time-point measured.The increase was attributed to peripheral adaptations, confirmed by a close correlation betweenchange in VO2 and change in a-v O2 diff. The first step of the circulatory response was typical ofnormal (early) cardiovascular drift, with increased HR and concomitantly decreased SV andVO2/HR, occurring over the first 4-6 h. The second step, which continued until approximately 12h, included reversed HR-drift, with normalization of SV and VO2/HR. When exercise continueduntil 50 h late cardiovascular drift was noted, characterized by increased VO2/HR, (indicatingmore efficient energy distribution), decreased peripheral resistance, increased stroke volume, anddecreased work of the heart. Since cardiac output was maintained at all time points we interpretthe changes as physiologically appropriate adaptations to ultra-endurance exercise.

  • 24. Montenegro, Marcelo F
    et al.
    Sundqvist, Michaela L
    Larsen, Filip J
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology, Research group for Mitokondriell funktion och metabolisk kontroll.
    Zhuge, Zhengbing
    Carlström, Mattias
    Weitzberg, Eddie
    Lundberg, Jon O
    Blood Pressure-Lowering Effect of Orally Ingested Nitrite Is Abolished by a Proton Pump Inhibitor.2017In: Hypertension, ISSN 0194-911X, E-ISSN 1524-4563, Vol. 69, no 1, p. 23-31Article in journal (Refereed)
    Abstract [en]

    Inorganic nitrate and nitrite from dietary and endogenous sources are metabolized to NO and other bioactive nitrogen oxides that affect blood pressure. The mechanisms for nitrite bioactivation are unclear, but recent studies in rodents suggest that gastric acidity may influence the systemic effects of this anion. In a randomized, double-blind, placebo-controlled crossover study, we tested the effects of a proton pump inhibitor on the acute cardiovascular effects of nitrite. Fifteen healthy nonsmoking, normotensive subjects, aged 19 to 39 years, were pretreated with placebo or esomeprazole (3×40 mg) before ingesting sodium nitrite (0.3 mg kg(-1)), followed by blood pressure monitoring. Nitrite reduced systolic blood pressure by a maximum of 6±1.3 mm Hg when taken after placebo, whereas pretreatment with esomeprazole blunted this effect. Peak plasma nitrite, nitrate, and nitroso species levels after nitrite ingestion were similar in both interventions. In 8 healthy volunteers, we then infused increasing doses of sodium nitrite (1, 10, and 30 nmol kg(-1) min(-1)) intravenously. Interestingly, although plasma nitrite peaked at similar levels as with orally ingested nitrite (≈1.8 µmol/L), no changes in blood pressure were observed. In rodents, esomeprazole did not affect the blood pressure response to the NO donor, DEA NONOate, or vascular relaxation to nitroprusside and acetylcholine, demonstrating an intact downstream NO-signaling pathway. We conclude that the acute blood pressure-lowering effect of nitrite requires an acidic gastric environment. Future studies will reveal if the cardiovascular complications associated with the use of proton pump inhibitors are linked to interference with the nitrate-nitrite-NO pathway.

  • 25.
    Moretti, Chiara
    et al.
    Karolinska Inst, Dept Physiol & Pharmacol, Stockholm, Sweden..
    Larsen, Filip J
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology, Research group for Mitokondriell funktion och metabolisk kontroll.
    Lundberg, Jon
    Karolinska Inst, Dept Physiol & Pharmacol, Stockholm, Sweden..
    Dietary nitrite extends lifespan in the fruit fly2019In: European Journal of Clinical Investigation,  Vol 49, Suppl 1, p 102, Meeting Abstract: P004-T, Wiley-Blackwell, 2019, Vol. 49, p. 102-102Conference paper (Other academic)
  • 26. Schiffer, Tomas A
    et al.
    Peleli, Maria
    Sundqvist, Michaela L
    Ekblom, Björn
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology, Björn Ekblom's research group.
    Lundberg, Jon O
    Weitzberg, Eddie
    Larsen, Filip J
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology, Research group for Mitokondriell funktion och metabolisk kontroll.
    Control of Human Energy Expenditure by Cytochrome C Oxidase Subunit IV-2.2016In: American Journal of Physiology - Cell Physiology, ISSN 0363-6143, E-ISSN 1522-1563, Vol. 311, no 3, p. C452-C461Article in journal (Refereed)
    Abstract [en]

    Resting metabolic rate (RMR) in human shows pronounced individual variations, but the underlying molecular mechanism remains elusive. Cytochrome C oxidase (COX) plays a key role in control of metabolic rate and recent studies of the subunit 4 isoform 2 (COX IV-2) indicate involvement in the cellular response to hypoxia and oxidative stress. We evaluated whether the COX subunit IV isoform composition may explain the pronounced individual variations in resting metabolic rate (RMR). RMR was determined in healthy humans by indirect calorimetry and correlated to levels of COX IV-2 and COX IV-1 in Vastus Lateralis. Over expression and knock down of the COX IV isoforms were performed in primary myotubes followed by evaluation of the cell respiration and production of reactive oxygen species. Here we show that COX IV-2 protein is constitutively expressed in human skeletal muscle and strongly correlated to RMR. Primary human myotubes overexpressing COX IV-2 displayed markedly (>60%) lower respiration, reduced (>50%) cellular H2O2 production, higher resistance towards both oxidative stress and severe hypoxia compared to control cells. These results suggest an important role of isoform COX IV-2 in the control of energy expenditure, hypoxic tolerance and mitochondrial ROS homeostasis in humans.

  • 27. Zinner, Christoph
    et al.
    Morales-Alamo, David
    Ørtenblad, Niels
    Larsen, Filip J
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology, Research group for Mitokondriell funktion och metabolisk kontroll.
    Schiffer, Tomas A
    Willis, Sarah J
    Gelabert-Rebato, Miriam
    Perez-Valera, Mario
    Boushel, Robert
    Calbet, Jose A L
    Holmberg, Hans-Christer
    The Physiological Mechanisms of Performance Enhancement with Sprint Interval Training Differ between the Upper and Lower Extremities in Humans.2016In: Frontiers in Physiology, ISSN 1664-042X, E-ISSN 1664-042X, Vol. 7, article id 426Article in journal (Refereed)
    Abstract [en]

    To elucidate the mechanisms underlying the differences in adaptation of arm and leg muscles to sprint training, over a period of 11 days 16 untrained men performed six sessions of 4-6 × 30-s all-out sprints (SIT) with the legs and arms, separately, with a 1-h interval of recovery. Limb-specific VO2peak, sprint performance (two 30-s Wingate tests with 4-min recovery), muscle efficiency and time-trial performance (TT, 5-min all-out) were assessed and biopsies from the m. vastus lateralis and m. triceps brachii taken before and after training. VO2peak and Wmax increased 3-11% after training, with a more pronounced change in the arms (P < 0.05). Gross efficiency improved for the arms (+8.8%, P < 0.05), but not the legs (-0.6%). Wingate peak and mean power outputs improved similarly for the arms and legs, as did TT performance. After training, VO2 during the two Wingate tests was increased by 52 and 6% for the arms and legs, respectively (P < 0.001). In the case of the arms, VO2 was higher during the first than second Wingate test (64 vs. 44%, P < 0.05). During the TT, relative exercise intensity, HR, VO2, VCO2, VE, and Vt were all lower during arm-cranking than leg-pedaling, and oxidation of fat was minimal, remaining so after training. Despite the higher relative intensity, fat oxidation was 70% greater during leg-pedaling (P = 0.017). The aerobic energy contribution in the legs was larger than for the arms during the Wingate tests, although VO2 for the arms was enhanced more by training, reducing the O2 deficit after SIT. The levels of muscle glycogen, as well as the myosin heavy chain composition were unchanged in both cases, while the activities of 3-hydroxyacyl-CoA-dehydrogenase and citrate synthase were elevated only in the legs and capillarization enhanced in both limbs. Multiple regression analysis demonstrated that the variables that predict TT performance differ for the arms and legs. The primary mechanism of adaptation to SIT by both the arms and legs is enhancement of aerobic energy production. However, with their higher proportion of fast muscle fibers, the arms exhibit greater plasticity.

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