Gymnastik- och idrottshögskolan, GIH

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  • 1.
    Apro, William
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Horwath, Oscar
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Granberg, Jonas
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Moberg, Marcus
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Andersson, Eva
    Swedish School of Sport and Health Sciences, GIH, Department of Physical Activity and Health.
    Ekblom, Björn
    Swedish School of Sport and Health Sciences, GIH.
    Intake Of Essential Amino Acids Stimulates Mtorc1 Signaling And Inhibits Autophagy Following Glycogen-depleted Resistance Exercise2020In: MEDICINE AND SCIENCE IN SPORTS AND EXERCISE. 52:17, Suppl. Meeting Abstract 125, Lippincott Williams & Wilkins, 2020, Vol. 52, no 17, p. 18-18Conference paper (Other academic)
  • 2.
    Blackwood, Sarah J
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Horwath, Oscar
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Moberg, Marcus
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics. Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden.
    Pontén, Marjan
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Apro, William
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics. Department of Clinical Science, Intervention and Technology, Karolinska Institutet, Stockholm, Sweden..
    Ekblom, Maria
    Swedish School of Sport and Health Sciences, GIH, Department of Physical Activity and Health. Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden..
    Larsen, Filip J
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Katz, Abram
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Extreme Variations in Muscle Fiber Composition Enable Detection of Insulin Resistance and Excessive Insulin Secretion.2022In: Journal of Clinical Endocrinology and Metabolism, ISSN 0021-972X, E-ISSN 1945-7197, Vol. 107, no 7, p. e2729-e2737, article id dgac221Article in journal (Refereed)
    Abstract [en]

    CONTEXT: Muscle fiber composition is associated with peripheral insulin action.

    OBJECTIVE: We investigated whether extreme differences in muscle fiber composition are associated with alterations in peripheral insulin action and secretion in young, healthy subjects who exhibit normal fasting glycemia and insulinemia.

    METHODS: Relaxation time following a tetanic contraction was used to identify subjects with a high or low expression of type I muscle fibers: group I (n=11), area occupied by type I muscle fibers = 61.0 ± 11.8%; group II (n=8), type I area = 36.0 ± 4.9% (P<0.001). Biopsies were obtained from the vastus lateralis muscle and analyzed for mitochondrial respiration on permeabilized fibers, muscle fiber composition and capillary density. An intravenous glucose tolerance test was performed and indices of glucose tolerance, insulin sensitivity and secretion were determined.

    RESULTS: Glucose tolerance was similar between groups, whereas whole-body insulin sensitivity was decreased by ~50% in group II vs group I (P=0.019). First phase insulin release (area under the insulin curve during 10 min after glucose infusion) was increased by almost 4-fold in group II vs I (P=0.01). Whole-body insulin sensitivity was correlated with % area occupied by type I fibers (r=0.54; P=0.018) and capillary density in muscle (r=0.61; P=0.005), but not with mitochondrial respiration. Insulin release was strongly related to % area occupied by type II fibers (r=0.93; P<0.001).

    CONCLUSIONS: Assessment of muscle contractile function in young healthy subjects may prove useful in identifying individuals with insulin resistance and enhanced glucose stimulated insulin secretion prior to onset of clinical manifestations.

  • 3.
    Blackwood, Sarah J
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Horwath, Oscar
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Moberg, Marcus
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics. Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden..
    Pontén, Marjan
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Apro, William
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics. Department of Clinical Science, Intervention and Technology, Karolinska Institutet, Stockholm, Sweden.
    Ekblom, Maria
    Swedish School of Sport and Health Sciences, GIH, Department of Physical Activity and Health. Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden..
    Larsen, Filip J
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Katz, Abram
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Insulin resistance after a 3-day fast is associated with an increased capacity of skeletal muscle to oxidize lipids.2023In: American Journal of Physiology. Endocrinology and Metabolism, ISSN 0193-1849, E-ISSN 1522-1555, Vol. 324, no 5, p. E390-E401Article in journal (Refereed)
    Abstract [en]

    There is a debate on whether lipid-mediated insulin resistance derives from an increased or decreased capacity of muscle to oxidize fats. Here we examine the involvement of muscle fiber composition in the metabolic responses to a 3-day fast (starvation, which results in increases in plasma lipids and insulin resistance) in two groups of healthy young subjects: 1, area occupied by type I fibers = 61.0 ± 11.8%; 2, type I area = 36.0 ± 4.9% (P<0.001). Muscle biopsies and intravenous glucose tolerance tests were performed after an overnight fast and after starvation. Biopsies were analyzed for muscle fiber composition and mitochondrial respiration. Indices of glucose tolerance and insulin sensitivity were determined. Glucose tolerance was similar in both groups after an overnight fast and deteriorated to a similar degree in both groups after starvation. In contrast, whole-body insulin sensitivity decreased markedly after starvation in group 1 (P<0.01), whereas the decrease in group 2 was substantially smaller (P=0.06). Non-esterified fatty acids and β-hydroxybutyrate levels in plasma after an overnight fast were similar between groups and increased markedly and comparably in both groups after starvation, demonstrating similar degrees of lipid load. The capacity of permeabilized muscle fibers to oxidize lipids was significantly higher in group 1 vs. 2, whereas there was no significant difference in pyruvate oxidation between groups. The data demonstrate that loss of whole-body insulin sensitivity after short-term starvation is a function of muscle fiber composition and is associated with an elevated rather than a diminished capacity of muscle to oxidize lipids.

  • 4.
    Cardinale, Daniele A.
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics. Elite Performance Centre, Bosön. Swedish Sports Confederation, Lidingö, Sweden.
    Horwath, Oscar
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Elings-Knutsson, Jona
    Karolinska Institutet, Stockholm, Sweden,.
    Helge, Torbjörn
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Godhe, Manne
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Bermon, Stéphane
    LAMHESS, Université Côte d’Azur, Nice, France.
    Moberg, Marcus
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Flockhart, Mikael
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Larsen, Filip J
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Hirschberg, Angelica Lindén
    Karolinska institutet, Stockholm, Sweden.
    Ekblom, Björn
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Enhanced Skeletal Muscle Oxidative Capacity and Capillary-to-Fiber Ratio Following Moderately Increased Testosterone Exposure in Young Healthy Women2020In: Frontiers in Physiology, E-ISSN 1664-042X, Vol. 11, article id 585490Article in journal (Refereed)
    Abstract [en]

    Background: Recently, it was shown that exogenously administered testosterone enhances endurance capacity in women. In this study, our understanding on the effects of exogenous testosterone on key determinants of oxygen transport and utilization in skeletal muscle is expanded.Methods: In a double-blinded, randomized, placebo-controlled trial, 48 healthy active women were randomized to 10 weeks of daily application of 10 mg of testosterone cream or placebo. Before and after the intervention, VO<sub>2</sub> max, body composition, total hemoglobin (Hb) mass and blood volumes were assessed. Biopsies from the vastus lateralis muscle were obtained before and after the intervention to assess mitochondrial protein abundance, capillary density, capillary-to-fiber (C/F) ratio, and skeletal muscle oxidative capacity.Results: Maximal oxygen consumption per muscle mass, Hb mass, blood, plasma and red blood cell volumes, capillary density, and the abundance of mitochondrial protein levels (i.e., citrate synthase, complexes I, II, III, IV-subunit 2, IV-subunit 4, and V) were unchanged by the intervention. However, the C/F ratio, specific mitochondrial respiratory flux activating complex I and linked complex I and II, uncoupled respiration and electron transport system capacity, but not leak respiration or fat respiration, were significantly increased following testosterone administration compared to placebo.Conclusion: This study provides novel insights into physiological actions of increased testosterone exposure on key determinants of oxygen diffusion and utilization in skeletal muscle of women. Our findings show that higher skeletal muscle oxidative capacity coupled to higher C/F ratio could be major contributing factors that improve endurance performance following moderately increased testosterone exposure.

  • 5.
    Davids, Charlie J
    et al.
    University of Queensland, Brisbane, Australia; Queensland Academy of Sport, Nathan, Australia.
    Næss, Tore C
    Department of Physical Performance, Norwegian School of Sport Science, Oslo, Norway..
    Moen, Maria
    Department of Physical Performance, Norwegian School of Sport Science, Oslo, Norway..
    Cumming, Kristoffer Toldnes
    Department of Physical Performance, Norwegian School of Sport Science, Oslo, Norway..
    Horwath, Oscar
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Psilander, Niklas
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Ekblom, Björn
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Coombes, Jeff S
    University of Queensland, Brisbane, Australia..
    Peake, Jonathan M
    Queensland Academy of Sport, Nathan, Australia; Queensland University of Technology, School of Biomedical Science, Brisbane, Australia.
    Raastad, Truls
    Department of Physical Performance, Norwegian School of Sport Science, Oslo, Norway..
    Roberts, Llion Arwyn
    University of Queensland, Brisbane, Australia; Queensland Academy of Sport, Nathan, Australia; Griffith University, Gold Coast, Australia.
    Acute cellular and molecular responses and chronic adaptations to low-load blood flow restriction and high-load resistance exercise in trained individuals.2021In: Journal of applied physiology, ISSN 8750-7587, E-ISSN 1522-1601, Vol. 131, no 6, p. 1731-1749Article in journal (Refereed)
    Abstract [en]

    Blood flow restriction (BFR) with low-load resistance exercise (RE) is often used as a surrogate to traditional high-load RE to stimulate muscular adaptations, such as hypertrophy and strength. However, it is not clear whether such adaptations are achieved through similar cellular and molecular processes. We compared changes in muscle function, morphology and signaling pathways between these differing training protocols. Twenty-one males and females (mean ± SD: 24.3 ± 3.1 years) experienced with resistance training (4.9 ± 2.6 years) performed nine weeks of resistance training (three times per week) with either high-loads (75-80% 1RM; HL-RT), or low-loads with BFR (30-40% 1RM; LL-BFR). Before and after the training intervention, resting muscle biopsies were collected, and quadricep cross-sectional area (CSA), muscular strength and power were measured. Approximately 5 days following the intervention, the same individuals performed an additional 'acute' exercise session under the same conditions, and serial muscle biopsies were collected to assess hypertrophic- and ribosomal-based signaling stimuli. Quadricep CSA increased with both LL-BFR (7.4±4.3%) and HL-RT (4.6±2.9%), with no significant differences between training groups (p=0.37). Muscular strength also increased in both training groups, but with superior gains in squat 1RM occurring with HL-RT (p<0.01). Acute phosphorylation of several key proteins involved in hypertrophy signaling pathways, and expression of ribosomal RNA transcription factors occurred to a similar degree with LL-BFR and HL-RT (all p>0.05 for between-group comparisons). Together, these findings validate low-load resistance training with continuous BFR as an effective alternative to traditional high-load resistance training for increasing muscle hypertrophy in trained individuals.

  • 6.
    Edman, Sebastian
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Horwath, Oscar
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Andersson, Alva
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Apro, William
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    THRIFTY; A Novel Method For Rapid Fiber Type Identification Of Isolated Skeletal Muscle Fibers2022In: Medicine & Science in Sports & Exercise 54(2022);Suppl. 2, Lippincott Williams & Wilkins, 2022, Vol. 54, no 9, p. 109-109, article id 457Conference paper (Other academic)
  • 7.
    Edman, Sebastian
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Horwath, Oscar
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Apro, William
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    THRIFTY - A High-throughput Single Muscle Fiber Typing Method Based on Immunofluorescence Detection2023In: Bio-protocol, E-ISSN 2331-8325, Vol. 13, no 10, article id e4678Article in journal (Refereed)
    Abstract [en]

    Skeletal muscle consists of a mixture of fiber types with different functional and metabolic characteristics. The relative composition of these muscle fiber types has implications for muscle performance, whole-body metabolism, and health. However, analyses of muscle samples in a fiber type-dependent manner are very time consuming. Therefore, these are often neglected in favor of more time-efficient analyses on mixed muscle samples. Methods such as western blot and myosin heavy chain separation by SDS-PAGE have previously been utilized to fiber type-isolated muscle fibers. More recently, the introduction of the dot blot method significantly increased the speed of fiber typing. However, despite recent advancements, none of the current methodologies are feasible for large-scale investigations because of their time requirements. Here, we present the protocol for a new method, which we have named THRIFTY (high-THRoughput Immunofluorescence Fiber TYping), that enables rapid fiber type identification using antibodies towards the different myosin heavy chain (MyHC) isoforms of fast and slow twitch muscle fibers. First, a short segment (<1 mm) is cut off from isolated muscle fibers and mounted on a customized gridded microscope slide holding up to 200 fiber segments. Second, the fiber segments attached to the microscope slide are stained with MyHC-specific antibodies and then visualized using a fluorescence microscope. Lastly, the remaining pieces of the fibers can either be collected individually or pooled together with fibers of the same type for subsequent analyses. The THRIFTY protocol is approximately three times as fast as the dot blot method, which enables not only time-sensitive assays to be performed but also increases the feasibility to conduct large-scale investigations into fiber type specific physiology.

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  • 8.
    Edman, Sebastian
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology.
    Horwath, Oscar
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology.
    Blomstrand, Eva
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology.
    Intake of branched-chain amino acids in combination with endurance exercise – no effect on mRNA expression of proteins regulating mitochondrial biogenesis2019Conference paper (Other academic)
  • 9.
    Edman, Sebastian
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Strömlind, Henrik
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Horwath, Oscar
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Apro, William
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Fiber type-specific signaling responses to nutritional and contractile stimuli in young and aged human skeletal muscleManuscript (preprint) (Other academic)
  • 10.
    Horwath, Oscar
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology.
    Apro, William
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology, Eva Blomstrand's research group.
    Moberg, Marcus
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology, Eva Blomstrand's research group.
    Godhe, Manne
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology, Björn Ekblom's research group.
    Helge, Torbjörn
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology, Björn Ekblom's research group.
    Ekblom, Maria
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Laboratory for Biomechanics and Motor Control.
    Lindén Hirschberg, Angelica
    Karolinska institutet.
    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.
    Fiber type-specific hypertrophy and increased capillarization in skeletal muscle following testosterone administration of young women.2020In: Journal of applied physiology, ISSN 8750-7587, E-ISSN 1522-1601, Vol. 128, no 5, p. 1240-1250Article in journal (Refereed)
    Abstract [en]

    It is well established that testosterone administration induces muscle fiber hypertrophy and myonuclear addition in men, however, it remains to be determined whether similar morphological adaptations can be achieved in women. The aim of the present study was therefore to investigate whether exogenously administered testosterone alters muscle fiber morphology in skeletal muscle of young healthy, physically active women. Thirty-five young (20-35 years), recreationally trained women were randomly assigned to either 10-week testosterone administration (10 mg daily) or placebo. Before and after the intervention, hormone concentrations and body composition were assessed, and muscle biopsies were obtained from the vastus lateralis. Fiber type composition, fiber size, satellite cell- and myonuclei content, as well as muscle capillarization were assessed in a fiber type-specific manner using immunohistochemistry. Following the intervention, testosterone administration elevated serum testosterone concentration (5.1-fold increase, P=0.001), and induced significant accretion of total lean mass (+1.9%, P=0.002) and leg lean mass (+2.4%, P=0.001). On the muscle fiber level, testosterone increased mixed fiber cross-sectional area (+8.2%, P=0.001), an effect primarily driven by increases in type II fiber size (9.2%, P=0.006). Whereas myonuclei content remained unchanged, a numerical increase (+30.8%) was found for satellite cells associated with type II fibers in the Testosterone group. In parallel with fiber hypertrophy, testosterone significantly increased capillary contacts (+7.5%, P=0.015) and capillary-to-fiber ratio (+9.2%, P=0.001) in type II muscle fibers. The current study provides novel insight into fiber type-specific adaptations present already after 10 weeks of only moderately elevated testosterone levels in women.

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  • 11.
    Horwath, Oscar
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Edman, Sebastian
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics. Åstrand Laboratory.
    Andersson, Alva
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Larsen, Filip J
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Apro, William
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics. Department of Clinical Science, Intervention and Technology, Karolinska Institutet, Stockholm, Sweden..
    THRIFTY: a novel high-throughput method for rapid fibre type identification of isolated skeletal muscle fibres.2022In: Journal of Physiology, ISSN 0022-3751, E-ISSN 1469-7793, Vol. 600, no 20, p. 4421-4438Article in journal (Refereed)
    Abstract [en]

    Fibre type-specific analyses are required for broader understanding of muscle physiology, but such analyses are difficult to conduct due to the extreme time requirements of dissecting and fibre typing individual fibres. Investigations are often confined to a small number of fibres from few participants with low representativeness of the entire fibre population and the participant population. To increase the feasibility of conducting large-scale fibre type-specific studies, a valid and rapid method for high-throughput fibre typing of individually dissected fibres was developed and named THRIFTY (for high-THRoughput Immunofluorescence Fibre TYping). Employing THRIFTY, 400 fibre segments were fixed onto microscope slides with a pre-printed coordinated grid system, probed with antibodies against myosin heavy chain (MyHC)-I and MyHC-II and classified using a fluorescence microscope. The validity and speed of THRIFTY was compared to a previously validated protocol (dot blot) on a fibre-to-fibre basis. Fibre pool purity was evaluated using 'gold standard' SDS-PAGE and silver staining. A modified THRIFTY-protocol using fluorescence western blot equipment was also validated. THRIFTY displayed excellent agreement with the dot blot protocol, κ = 0.955 (95% CI: 0.928, 0.982), P < 0.001. Both the original and modified THRIFTY protocols generated type I and type II fibre pools of absolute purity. Using THRIFTY, 400 fibres were typed just under 11 h, which was approximately 3 times faster than dot blot. THRIFTY is a novel and valid method with high versatility for very rapid fibre typing of individual fibres. THRIFTY can therefore facilitate the generation of large fibre pools for more extensive mechanistic studies into skeletal muscle physiology. KEY POINTS: Skeletal muscle is composed of different fibre types, each with distinct physiological properties. To fully understand how skeletal muscle adapts to external cues such as exercise, nutrition and ageing, fibre type-specific investigations are required. Such investigations are very difficult to conduct due to the extreme time requirements related to classifying individually isolated muscle fibres. To bypass this issue, we have developed a rapid and reliable method named THRIFTY which is cheap as well as versatile and which can easily be implemented in most laboratories. THRIFTY increases the feasibility of conducting larger fibre type-specific studies and enables time-sensitive assays where measurements need to be carried out in close connection with tissue sampling. By using THRIFTY, new insights into fibre type-specific muscle physiology can be gained which may have broad implications in health and disease.

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  • 12.
    Horwath, Oscar
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Envall, Helena
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics. Student.
    Röja, Julia
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics. Student.
    Emanuelsson, Eric Bengt
    Karolinska Institute, Sweden.
    Sanz, Gema
    Karolinska Institute, Sweden.
    Ekblom, Björn
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Apro, William
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics. Karolinska Institute, Sweden.
    Moberg, Marcus
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics. Karolinska Institute, Sweden.
    Variablity in vastus lateralis fiber type distribution, fiber size and myonuclear content along and between the legs.2021In: Journal of applied physiology, ISSN 8750-7587, E-ISSN 1522-1601, Vol. 131, no 1, p. 158-173Article in journal (Refereed)
    Abstract [en]

    Human skeletal muscle characteristics such as fiber type composition, fiber size and myonuclear content are widely studied in clinical and sports related contexts. Being aware of the methodological and biological variability of the characteristics is a critical aspect in study design and outcome interpretation, but comprehensive data on the variability of morphological features in human skeletal muscle is currently limited. Accordingly, in the present study, m. vastus lateralis biopsies (10 per subject) from young and healthy individuals, collected in a systematic manner, were analyzed for various characteristics using immunohistochemistry (n=7) and SDS-PAGE (n=25). None of the analyzed parameters; fiber type % (FT%), type I and II CSA (fCSA), percentage fiber type area (fCSA%), myosin heavy chain composition (MyHC%), type IIX content, myonuclear content or myonuclear domain varied in a systematic manner longitudinally along the muscle or between the two legs. The average within subject coefficient of variation for FT%, fCSA, fCSA%, and MyHC% ranged between 13-18%, but was only 5% for fiber specific myonuclear content, which reduced the variability for myonuclear domain size to 11-12%. Pure type IIX fibers and type IIX MyHC were randomly distributed and present in <24% of the analyzed samples, with the average content being 0.1 and 1.1%, respectively. In conclusion, leg or longitudinal orientation does not seem to be an important aspect to consider when investigating human vastus lateralis characteristics. However, single muscle biopsies should preferably not be used when studying fiber type and fiber size related aspects given the notable sample to sample variability.

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  • 13.
    Horwath, Oscar
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology.
    Granberg, Jonas
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology.
    Apro, William
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology.
    Low Glycogen Availability Increases Autophagy Signalling Following Resistance Exercise2019Conference paper (Other academic)
  • 14.
    Horwath, Oscar
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Moberg, Marcus
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics. Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden.
    Hirschberg, Angelica Lindén
    Department of Women´s and Children´s Health, Division of Neonatology, Obstetrics and Gynaecology, Karolinska Institutet, Stockholm, Sweden; Department of Gynaecology and Reproductive Medicine, Karolinska University Hospital, Stockholm, Sweden..
    Ekblom, Björn
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Apro, William
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics. Department of Clinical Science, Intervention and Technology, Karolinska Institutet, Stockholm, Sweden..
    Molecular Regulators of Muscle Mass and Mitochondrial Remodeling Are Not Influenced by Testosterone Administration in Young Women.2022In: Frontiers in Endocrinology, E-ISSN 1664-2392, Vol. 13, article id 874748Article in journal (Refereed)
    Abstract [en]

    Testosterone (T) administration has previously been shown to improve muscle size and oxidative capacity. However, the molecular mechanisms underlying these adaptations in human skeletal muscle remain to be determined. Here, we examined the effect of moderate-dose T administration on molecular regulators of muscle protein turnover and mitochondrial remodeling in muscle samples collected from young women. Forty-eight healthy, physically active, young women (28 ± 4 years) were assigned in a random double-blind fashion to receive either T (10 mg/day) or placebo for 10-weeks. Muscle biopsies collected before and after the intervention period were divided into sub-cellular fractions and total protein levels of molecular regulators of muscle protein turnover and mitochondrial remodeling were analyzed using Western blotting. T administration had no effect on androgen receptor or 5α-reductase levels, nor on proteins involved in the mTORC1-signaling pathway (mTOR, S6K1, eEF2 and RPS6). Neither did it affect the abundance of proteins associated with proteasomal protein degradation (MAFbx, MuRF-1 and UBR5) and autophagy-lysosomal degradation (AMPK, ULK1 and p62). T administration also had no effect on proteins in the mitochondria enriched fraction regulating mitophagy (Beclin, BNIP3, LC3B-I, LC3B-II and LC3B-II/I ratio) and morphology (Mitofilin), and it did not alter the expression of mitochondrial fission- (FIS1 and DRP1) or fusion factors (OPA1 and MFN2). In summary, these data indicate that improvements in muscle size and oxidative capacity in young women in response to moderate-dose T administration cannot be explained by alterations in total expression of molecular factors known to regulate muscle protein turnover or mitochondrial remodeling.

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  • 15.
    Horwath, Oscar
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Moberg, Marcus
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Larsen, Filip J
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Philp, Andrew
    Garvan Institute of Medical Research, Darlinghurst, Sydney, New South Wales, Australia.
    Apro, William
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics. Karolinska institutet, Sweden.
    Ekblom, Björn
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Influence of sex- and fiber type on the satellite cell pool in human skeletal muscle.2021In: Scandinavian Journal of Medicine and Science in Sports, ISSN 0905-7188, E-ISSN 1600-0838, Vol. 31, no 2, p. 303-312Article in journal (Refereed)
    Abstract [en]

    The repair, remodeling and regeneration of myofibers is dependent on satellite cells (SCs), although, the distribution of SCs in different fiber types of human muscle remains inconclusive. There is also a paucity of research comparing muscle fiber characteristics in a sex-specific manner. Therefore, the aim of this study was to investigate fiber type-specific SC content in men and women. Muscle biopsies from vastus lateralis were collected from 64 young (mean age 27 ± 5), moderately trained men (n=34) and women (n=30). SCs were identified by Pax7-staining together with immunofluorescent analyses of fiber type composition, fiber size and myonuclei content. In a mixed population, comparable number of SCs were associated to type I and type II fibers (0.07 ± 0.02 vs 0.07 ± 0.02 SCs per fiber, respectively). However, unlike men, women displayed a fiber type-specific distribution, with SC content being lower in type II than type I fibers (P=0.041). Sex-based differences were found specifically for type II fibers, where women displayed lower SC content compared to men (P<0.001). In addition, positive correlations (r-values between 0.36-0.56) were found between SC content and type I and type II fiber size in men (P=0.03 and P<0.01, respectively), whereas similar relationships could not be detected in women. Sex-based differences were also noted for fiber type composition and fiber size, but not for myonuclei content. We hereby provide evidence for sex-based differences present at the myocellular level, which may have important implications when studying exercise- and training induced myogenic responses in skeletal muscle.

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  • 16.
    Horwath, Oscar
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Nordström, Fabian
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Apro, William
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Moberg, Marcus
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Satellite cell pool expansion induced by resistance exercise is not altered by acute normobaric hypoxia2022In: Svensk idrottsmedicin 2022:2, Svensk förening för fysisk aktivitet och idrottsmedicin , 2022, Vol. 41, p. 30-Conference paper (Other academic)
  • 17.
    Horwath, Oscar
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Nordström, Fabian
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    von Walden, Ferdinand
    Division of Pediatric Neurology, Department of Women's and Children's Health, Karolinska Institutet, Stockholm, Sweden..
    Apro, William
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics. Department of Clinical Science, Intervention and Technology, Karolinska Institutet, Solna, Sweden..
    Moberg, Marcus
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics. Department of Physiology and Pharmacology, Karolinska Institutet, Solna, Sweden..
    Acute hypoxia attenuates resistance exercise-induced ribosome signaling but does not impact satellite cell pool expansion in human skeletal muscle.2023In: The FASEB Journal, ISSN 0892-6638, E-ISSN 1530-6860, Vol. 37, no 3, article id e22811Article in journal (Refereed)
    Abstract [en]

    Cumulative evidence supports the hypothesis that hypoxia acts as a regulator of muscle mass. However, the underlying molecular mechanisms remain incompletely understood, particularly in human muscle. Here we examined the effect of hypoxia on signaling pathways related to ribosome biogenesis and myogenic activity following an acute bout of resistance exercise. We also investigated whether hypoxia influenced the satellite cell response to resistance exercise. Employing a randomized, crossover design, eight men performed resistance exercise in normoxia (FiO2 21%) or normobaric hypoxia (FiO2 12%). Muscle biopsies were collected in a time-course manner (before, 0, 90, 180 min and 24 h after exercise) and were analyzed with respect to cell signaling, gene expression and satellite cell content using immunoblotting, RT-qPCR and immunofluorescence, respectively. In normoxia, resistance exercise increased the phosphorylation of RPS6, TIF-1A and UBF above resting levels. Hypoxia reduced the phosphorylation of these targets by ~37%, ~43% and ~ 67% throughout the recovery period, respectively (p < .05 vs. normoxia). Resistance exercise also increased 45 S pre-rRNA expression and mRNA expression of c-Myc, Pol I and TAF-1A above resting levels, but no differences were observed between conditions. Similarly, resistance exercise increased mRNA expression of myogenic regulatory factors throughout the recovery period and Pax7+ cells were elevated 24 h following exercise in mixed and type II muscle fibers, with no differences observed between normoxia and hypoxia. In conclusion, acute hypoxia attenuates ribosome signaling, but does not impact satellite cell pool expansion and myogenic gene expression following a bout of resistance exercise in human skeletal muscle.

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  • 18.
    Jonsson, William O
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Ponette, Jonathan
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Horwath, Oscar
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Rydenstam, Tomas
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Söderlund, Karin
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Ekblom, Björn
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Azzolini, Michele
    Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden.
    Ruas, Jorge L
    Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden.
    Blomstrand, Eva
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics. Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden.
    Changes in plasma concentration of kynurenine following intake of branched-chain amino acids are not caused by alterations in muscle kynurenine metabolism.2022In: American Journal of Physiology - Cell Physiology, ISSN 0363-6143, E-ISSN 1522-1563, Vol. 322, p. C49-C62Article in journal (Refereed)
    Abstract [en]

    Administration of branched-chain amino acids (BCAA) has been suggested to enhance mitochondrial biogenesis, including levels of PGC-1α, which may, in turn, alter kynurenine metabolism. Ten healthy subjects performed 60 min of dynamic one-leg exercise at ~70% of Wmax on two occasions. They were in random order supplied either a mixture of BCAA or flavored water (placebo) during the experiment. Blood samples were collected during exercise and recovery, and muscle biopsies were taken from both legs before, after and 90 and 180 min following exercise. Ingestion of BCAA doubled their concentration in both plasma and muscle while causing a 30-40% reduction (P<0.05 vs. placebo) in levels of aromatic amino acids in both resting and exercising muscle during 3-h recovery. The muscle concentration of kynurenine decreased by 25% (P<0.05) during recovery, similar in both resting and exercising leg and with both supplements, although plasma concentration of kynurenine during recovery was 10% lower (P<0.05) when BCAA were ingested. Ingestion of BCAA reduced the plasma concentration of kynurenic acid by 60% (P<0.01) during exercise and recovery, while the level remained unchanged with placebo. Exercise induced a 3-4-fold increase (P<0.05) in muscle content of PGC-1a1 mRNA after 90 min of recovery under both conditions, whereas levels of KAT4 mRNA and protein were unaffected by exercise or supplement. In conclusion, the reduction of plasma levels of kynurenine and kynurenic acid caused by BCAA were not associated with any changes in the level of muscle kynurenine, suggesting that kynurenine metabolism was altered in tissues other than muscle.

  • 19.
    Moberg, Marcus
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics. Department of Physiology and Pharmacology, Karolinska Institute, Sweden.
    Apro, William
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics. Department of Clinical Science, Intervention and Technology, Karolinska Institute, Sweden.
    Horwath, Oscar
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    van Hall, Gerrit
    University of Copenhagen, Denmark.; Rigshospitalet, Copenhagen, Denmark..
    Blackwood, Sarah J
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Katz, Abram
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Acute normobaric hypoxia blunts contraction-mediated mTORC1- and JNK-signaling in human skeletal muscle.2022In: Acta Physiologica, ISSN 1748-1708, E-ISSN 1748-1716, Vol. 234, no 2, article id e13771Article in journal (Refereed)
    Abstract [en]

    AIM: Hypoxia has been shown to reduce resistance exercise-induced stimulation of protein synthesis and long-term gains in muscle mass. However, the mechanism whereby hypoxia exerts its effect is not clear. Here we examine the effect of acute hypoxia on the activity of several signaling pathways involved in regulation of muscle growth following a bout of resistance exercise.

    METHODS: Eight men performed two sessions of leg resistance exercise in Normoxia or Hypoxia (12% O2 ) in a randomized crossover fashion. Muscle biopsies were obtained at rest and at 0, 90,180 min after exercise. Muscle analyses included levels of signaling proteins and metabolites associated with energy turnover.

    RESULTS: Exercise during Normoxia induced a 5-10-fold increase of S6K1Thr389 phosphorylation throughout the recovery period, but Hypoxia blunted the increases by ~50%. Phosphorylation of JNKThr183/Tyr185 and the JNK target SMAD2Ser245/250/255 was increased by 30-40-fold immediately after exercise in Normoxia, but Hypoxia blocked almost 70% of the activation. Throughout recovery, phosphorylation of JNK and SMAD2 remained elevated following exercise in Normoxia, but the effect of Hypoxia was lost at 90-180 min post-exercise. Hypoxia had no effect on exercise induced Hippo- or autophagy-signaling and ubiquitin-proteasome related protein levels. Nor did Hypoxia alter the changes induced by exercise in high energy phosphates, glucose 6-P, lactate, or phosphorylation of AMPK or ACC.

    CONCLUSION: We conclude that acute severe hypoxia inhibits resistance exercise induced mTORC1- and JNK signaling in human skeletal muscle, effects that do not appear to be mediated by changes in the degree of metabolic stress in the muscle.

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  • 20.
    Valente-Silva, Paula
    et al.
    Karolinska Institutet, Stockholm, Sweden.
    Cervenka, Igor
    Karolinska Institutet, Stockholm, Sweden.
    Ferreira, Duarte M S
    Karolinska Institutet, Stockholm, Sweden.
    Correia, Jorge C
    Karolinska Institutet, Stockholm, Sweden.
    Edman, Sebastian
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Horwath, Oscar
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Heng, Benjamin
    Macquarie University, Sidney, Australia.
    Chow, Sharron
    Macquarie University, Sidney, Australia.
    Jacobs, Kelly R
    Macquarie University, Sidney, Australia.
    Guillemin, Gilles J
    Macquarie University, Sidney, Australia.
    Blomstrand, Eva
    Swedish School of Sport and Health Sciences, GIH, Department of Physiology, Nutrition and Biomechanics.
    Ruas, Jorge L
    Karolinska Institutet, Stockholm, Sweden.
    Effects of Tryptophan Supplementation and Exercise on the Fate of Kynurenine Metabolites in Mice and Humans.2021In: Metabolites, ISSN 2218-1989, E-ISSN 2218-1989, Vol. 11, no 8, article id 508Article in journal (Refereed)
    Abstract [en]

    The kynurenine pathway of tryptophan (TRP) degradation (KP) generates metabolites with effects on metabolism, immunity, and mental health. Endurance exercise training can change KP metabolites by changing the levels of KP enzymes in skeletal muscle. This leads to a metabolite pattern that favors energy expenditure and an anti-inflammatory immune cell profile and reduces neurotoxic metabolites. Here, we aimed to understand if TRP supplementation in untrained vs. trained subjects affects KP metabolite levels and biological effects. Our data show that chronic TRP supplementation in mice increases all KP metabolites in circulation, and that exercise reduces the neurotoxic branch of the pathway. However, in addition to increasing wheel running, we did not observe other effects of TRP supplementation on training adaptations, energy metabolism or behavior in mice. A similar increase in KP metabolites was seen in trained vs. untrained human volunteers that took a TRP drink while performing a bout of aerobic exercise. With this acute TRP administration, TRP and KYN were higher in the trained vs. the untrained group. Considering the many biological effects of the KP, which can lead to beneficial or deleterious effects to health, our data encourage future studies of the crosstalk between TRP supplementation and physical exercise.

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