Niels Ortenblad

Niels Ortenblad
University of Southern Denmark | SDU · Institute of Sports Science and Clinical Biomechanics

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125
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Publications (125)
Article
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The 70-kDa heat shock protein (HSP70) is a ubiquitous molecular chaperone which is highly inducible by cellular stress such as exercise. To investigate the role of muscle glycogen content on the HSP70 expression, muscle glycogen was manipulated by consumption of either water (H2O) or a carbohydrate-enriched diet (CHO) during recovery from 4 h of gl...
Article
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The present study examined skeletal muscle metabolism and changes in repeated sprint performance during match play for n = 20 competitive elite women outfield players. We obtained musculus vastus lateralis biopsies and blood samples before, after, and following intense periods in each half of a friendly match, along with 5 × 30‐meter sprint tests a...
Article
With the use of transmission electron microscopy, high-resolution images of fixed samples containing individual muscle fibers can be obtained. This enables quantifications of ultrastructural aspects such as volume fractions, surface area to volume ratios, morphometry, and physical contact sites of different subcellular structures. In the 1970s, a p...
Preprint
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Glycogen is a key energy substrate in excitable tissue and especially in skeletal muscle fibers it contributes with a substantial, but also local energy production. A heterogenic subcellular distribution of three distinct glycogen pools in skeletal muscle is proved by transmission electron microscopy (TEM), which is thought to represent the require...
Article
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Muscle glycogen is the main substrate during high-intensity exercise and large reductions can occur after relatively short durations. Moreover, muscle glycogen is stored heterogeneously and similarly displays a heterogeneous and fiber-type specific depletion pattern with utilization in both fast- and slow-twitch fibers during high-intensity exercis...
Article
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Cross-country (XC) ski races involve a variety of formats, two different techniques and tracks with highly variable topography and environmental conditions. In addition, XC skiing is a major component of both Nordic combined and biathlon competitions. Research in this area, both in the laboratory and field, encounters certain difficulties that may...
Article
Aim: The maintenance of healthy and functional mitochondria is the result of a complex mitochondrial turnover and herein quality-control program which includes both mitochondrial biogenesis and autophagy of mitochondria. The aim of this study was to examine the effect of an intensified training load on skeletal muscle mitochondrial quality control...
Article
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Objective NAD⁺ is a co-factor and substrate for enzymes maintaining energy homeostasis. Nicotinamide phosphoribosyltransferase (NAMPT) controls NAD⁺ synthesis, and in skeletal muscle, NAD⁺ is important for muscle integrity. However, the underlying molecular mechanisms by which NAD⁺ synthesis affects muscle health remain poorly understood. Thus, the...
Article
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Introduction Little is known about potential differences in contractile properties of muscle fibers of the same type in arms and legs. Accordingly, the present study was designed to compare the force-generating capacity and Ca ²⁺ sensitivity of fibers from arm and leg muscles of highly trained cross-country skiers. Method Single muscle fibers of m...
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Objective: To explore the relationship between the contents of subcellular localization specific mitochondria (mitochondria between myofibrils, mitochondria under the muscle membrane, total mitochondria) and different muscle fiber types, and the effect of short-term diet intervention on the content of subcellular localization specific mitochondria...
Article
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Ischaemic preconditioning (IPC) protects against myocardial ischaemia–reperfusion injury. The metabolic and ionic effects of IPC remain to be clarified in detail. We aimed to investigate the effect of IPC (2 times 5 min ischaemia) on the subcellular distribution of glycogen and Ca2+-uptake and leakiness by the sarcoplasmic reticulum (SR) in respons...
Article
New findings: What is the central question of this study? Glycogen supercompensation following glycogen-depleting exercise can be achieved by consuming a carbohydrate-enriched diet, but the associated effects on the size, number and localization of intramuscular glycogen particles is unknown. What is the main finding and its importance? Using tran...
Article
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Growing evidence supports that pharmacological application of growth differentiation factor 15 (GDF15) suppresses appetite but also promotes sickness-like behaviors in rodents via GDNF family receptor α-like (GFRAL)-dependent mechanisms. Conversely, the endogenous regulation of GDF15 and its physiological effects on energy homeostasis and behavior...
Article
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Context Women show an accelerated loss of muscle mass around menopause, possibly related to the decline in estrogen. Furthermore, the anabolic response to resistance exercise seems to be hampered in postmenopausal women. Objective We aimed to test the hypothesis that transdermal estrogen therapy (ET) amplifies the skeletal muscle response to resis...
Article
In this study, we examined the effect of beta 2 -agonist salbutamol at oral doses during a period of resistance training on sprint performance, quadriceps contractile function, skeletal muscle hypertrophy, fiber-type composition, maximal activity of enzymes of importance for anaerobic energy turnover, and sarcoplasmic reticulum Ca ²⁺ -handling in y...
Preprint
Full-text available
Growing evidence supports that pharmacological application of growth differentiation factor 15 (GDF15) suppresses appetite but also promotes sickness-like behaviors in rodents via GDNF family receptor α-like (GFRAL)-dependent mechanisms 1,2 . Conversely, the endogenous regulation and secretion of GDF15 and its physiological effects on energy homeos...
Article
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Objective: to determine whether skeletal muscle molecular markers and SC number were influenced differently in users and non-users of oral contraceptives (OCs) following 10 weeks of resistance training Methods: Thirty-eight young healthy untrained users (n=20) and non-users of OC (n=18) completed a 10-week supervised progressive resistance training...
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Aim: Glycogen particles are found in different subcellular localizations, which are utilized heterogeneously in different fibre types during endurance exercise. Although resistance exercise typically involves only a moderate use of mixed muscle glycogen, the hypothesis of the present study was that high-volume heavy-load resistance exercise would...
Article
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Background: Protein supplementation has been suggested to augment endurance training adaptations by increasing mixed muscle and myofibrillar protein synthesis and lean body mass. However, a potential beneficial effect on mitochondrial adaptations is yet to be clarified. The aim of the present study was to investigate the effect of consuming whey p...
Article
Background Long-term testosterone replacement therapy (TRT) increases muscle mass in elderly men with subnormal testosterone levels. However, the molecular mechanisms underlying this effect of TRT on protein balance in human skeletal muscle in vivo remain to be established. Methods Here, we examined skeletal muscle biopsies obtained before and 24-...
Article
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Little is presently known about the effects of acute high-intensity exercise or training on release and uptake of Ca 2+ by the sarcoplasmic reticulum (SR). The aims here were to characterize this regulation in highly trained athletes following (1) repeated bouts of high-intensity exercise and (2) a period of endurance training including high-intens...
Article
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Little is presently known about the effects of acute high-intensity exercise or training on release and uptake of Ca 2+ by the sarcoplasmic reticulum (SR). The aims here were to characterize this regulation in highly trained athletes following (1) repeated bouts of high-intensity exercise and (2) a period of endurance training including high-intens...
Article
Key points: When muscle biopsies first began to be used routinely in research on exercise physiology five decades ago, it soon become clear that the muscle content of glycogen is an important determinant of exercise performance. Glycogen particles are stored in distinct pools within the muscles, but the role of each pool during exercise and how th...
Preprint
Full-text available
Background: Protein supplementation has been suggested to augment endurance training adaptations by increasing mixed muscle and myofibrillar protein synthesis and lean body mass. However, a potential beneficial effect on mitochondrial adaptations is yet to be clarified. The aim of the present study was to investigate the effect of consuming whey pr...
Preprint
Full-text available
Background: Protein supplementation has been suggested to augment endurance training adaptations by increasing mixed muscle and myofibrillar protein synthesis and lean body mass. However, a potential beneficial effect on mitochondrial adaptations is yet to be clarified. The aim of the present study was to investigate the effect of consuming whey pr...
Article
Intramuscular triglycerides (IMTG) are a key substrate during prolonged exercise, but little is known about the rate of IMTG resynthesis in the post-exercise period. We investigated the hypothesis that the distribution of the lipid droplet (LD)-associated perilipin (PLIN) proteins is linked to IMTG storage following exercise. 14 elite male triathle...
Article
Key points: Muscle glycogen content is associated with muscle function, but the physiological link between the two is poorly understood. This study investigated the effects of inhibiting glycogenolysis, while maintaining high overall energy status, on different aspects of muscle function. We demonstrate here that Na+ ,K+ -ATPase activity depends o...
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Introduction: Ca2+ regulatory excitation-contraction coupling properties are key topics of interest in the development of work-related muscle myalgia and may constitute an underlying cause of muscle pain and loss of force generating capacity. Method: A well-established rat model of high repetition high force (HRHF) work was used to investigate i...
Article
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Carbohydrate (CHO) restricted training has been shown to increase the acute training response, whereas less is known about the acute effects after repeated CHO restricted training. On two occasions, the acute responses to CHO restriction were examined in endurance athletes. Study 1 examined cellular signaling and metabolic responses after seven tra...
Article
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As one of the most physically demanding sports in the Olympic Games, cross-country skiing poses considerable challenges with respect to both force generation and endurance during the combined upper- and lower-body effort of varying intensity and duration. The isoforms of myosin in skeletal muscle have long been considered not only to define the con...
Article
This study compared the effects of moderate-intensity endurance training and high-intensity interval training on fiber type-specific subcellular volumetric content and morphology of lipid droplets and mitochondria in skeletal muscles of type 2 diabetic patients. Sixteen sedentary type 2 diabetic patients (57{plus minus}7 years old) were randomized...
Conference Paper
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RESTRICTING CARBOHYDRATE DURING RECOVERY FROM PROLONGED EXERCISE DOES NOT EFFECT INTRAMUSCULAR TRIGLYCERIDE RESYNTHESIS. JEVONS, E.F.P.1, GEJL, K.D.2, HVID, L.G.2, FRANDSEN, U.2, JENSEN, K.2, SAHLIN, K.2, STRAUSS, J.A.1, ORTENBLAD, N.2, SHEPHERD, S.O.1 LIVERPOOL JOHN MOORES UNIVERSITY INTRODUCTION: Intramuscular triglycerides are an important sub...
Article
While short-term disuse negatively affects mechanical muscle function (e.g. isometric muscle strength) little is known of the relative contribution of adaptions in central neural drive and peripheral muscle contractility. The present study investigated the relative contribution of adaptations in central neural drive and peripheral muscle contractil...
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The purpose was to assess the impact of various factors on methodological errors associated with measurement of maximal oxidative phosphorylation (OXPHOS) in human skeletal muscle determined by high-resolution respirometry in saponin-permeabilized fibers. Biopsies were collected from 25 men to assess differences in OXPHOS between two muscle bundles...
Article
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Superfast muscles (SFMs) are extremely fast synchronous muscles capable of contraction rates up to 250 Hz, enabling precise motor execution at the millisecond time scale. SFM phenotypes have been discovered in most major vertebrate lineages, but it remains unknown whether all SFMs share excitation-contraction coupling pathway adaptations for speed,...
Article
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Key points: We investigated whether intramuscular temperature affects the acute recovery of exercise performance following fatigue-induced by endurance exercise. Mean power output was better preserved during an all-out arm-cycling exercise following a 2 h recovery period in which the upper arms were warmed to an intramuscular temperature of ̴ 38°C...
Article
In this issue of Acta Physiologica, a paper by Meinild and colleagues¹ aims to verify if the increase in mitochondrial content with endurance training is explained by mitochondrial remodelling (hypertrophy) or by a distinct biogenesis of new organelle structures. Mitochondria are membrane-enclosed organelles found in most cells, with a double membr...
Article
The purpose of the study was to investigate which physiological parameters would most accurately predict a 6-min, all-out, double-poling (DP) performance in recreational cross-country skiers. Twelve male recreational cross-country skiers performed tests consisting of three series lasting 10 s, one lasting 60 s, plus a 6-min, all-out, DP performance...
Article
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Purpose: The present study investigated the effects of periodic CHO restriction on endurance performance and metabolic markers in elite endurance athletes. Methods: Twenty-six male elite endurance athletes (VO2max: 65.0 ml O2[BULLET OPERATOR]kg[BULLET OPERATOR]min) completed 4 weeks of regular endurance training, while matched and randomized int...
Article
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Key points: Although lipid droplets in skeletal muscle are an important energy source during endurance exercise, our understanding of lipid metabolism in this context remains incomplete. Using transmission electron microscopy, two distinct subcellular pools of lipid droplets can be observed in skeletal muscle - one beneath the sarcolemma and the o...
Preprint
Superfast muscles (SFM) are extremely fast synchronous muscles capable of contraction rates up to 250 Hz, enabling precise motor execution at the millisecond time scale. To allow such speed, the archetypal SFM, found in the toadfish swimbladder, has hallmark structural and kinetic adaptations at each step of the conserved excitation-contraction cou...
Article
The cover image, by E. Andersson et al., is based on the Original Article Energy system contributions and determinants of performance in sprint cross-country skiing, DOI: 10.1111/sms.12666.
Article
The cytoskeleton is an integral part of skeletal muscle structure, and reorganization of the cytoskeleton occurs during various modes of remodeling. We previously found that the extracellular matrix protein secreted protein acidic and rich in cysteine (SPARC) is up-regulated and expressed intracellularly in developing muscle, during regeneration an...
Article
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Key points: In human skeletal muscles, the current view is that the capacity for mitochondrial energy production, and thus endurance capacity, is set by the mitochondria volume. However, increasing the mitochondrial inner membrane surface comprises an alternative mechanism for increasing the energy production capacity. In the present study, we sho...
Article
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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 VO 2 peak, sprint performance (two 30-s Wingate tests...
Article
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Key points: Glycogen is stored in local spatially distinct compartments within skeletal muscle fibres and is the main energy source during supramaximal exercise. Using quantitative electron microscopy, we show that supramaximal exercise induces a differential depletion of glycogen from these compartments and also demonstrate how this varies with f...
Article
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Purpose: To examine the metabolic responses and pacing strategies during the performance of successive sprint time trials (STTs) in cross-country skiing. Methods: Ten well-trained male cross-country skiers performed four self-paced 1300-m STTs on a treadmill, each separated by 45 min of recovery. The simulated STT course was divided into three f...
Article
Muscle fatigue has been studied with a variety approaches, tools and technologies. The foci of these studies have ranged tremendously, from molecules to the entire organism. Single cell and animal models have been used to gain mechanistic insight into the fatigue process. The theme of this review is the concept that the mechanisms of muscle fatigue...
Article
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To improve current understanding of energy contributions and determinants of sprint-skiing performance, 11 well-trained male cross-country skiers were tested in the laboratory for VO2max, submaximal gross efficiency (GE), maximal roller-skiing velocity, and sprint time-trial (STT) performance. The STT was repeated four times on a 1300-m simulated...
Article
The importance of glycogen, as a fuel during exercise, is a fundamental concept in exercise physiology. The use of electron microscopy has revealed that glycogen is not evenly distributed in skeletal muscle fibers, but rather localized in distinct pools. In this review, we present the available evidence regarding the subcellular localization of gly...
Article
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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. Althou...
Article
Introduction: Skeletal muscle is changed after stroke, but conflicting data exist concerning muscle morphology and oxidative enzymatic capacity. Methods: In 36 chronic stroke patients bilateral muscle biopsies were analysed, and fiber type proportions and cross sectional areas were determined by ATPase histochemistry. Enzymatic concentrations of...
Article
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The study was a randomized placebo-controlled trial investigating mechanisms by which chronic β2-adrenergic stimulation enhances muscle force and power output during maximal cycle ergometer exercise in young men. Eighteen trained men were assigned to an experimental group (oral terbutaline 5 mg∙30 kgbw(-1) twice daily; TER, n=9) or a control group...
Article
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The effects of short-term high-intensity exercise on single fiber contractile function in humans are unknown. Therefore, the purposes of this study were: (a) to access the acute effects of repeated high-intensity exercise on human single muscle fiber contractile function; and (b) to examine whether contractile function was affected by alterations i...