Nikolai Nordsborg

University of Copenhagen · Department of Nutrition, Exercise and Sports

The objective of this randomized controlled trial was to examine if exercise training can counteract energy restriction‐induced impairment of mitochondrial capacity in skeletal muscle of 55–70‐years people with prediabetes and metabolic syndrome. The potential impact of sex was explored. Fifty sedentary men and women with prediabetes and metabolic...

This study aimed to investigate the impact of swim training intensity and duration on cardiac structure and function in mildly hypertensive women. Sixty‐two mildly hypertensive women were randomized to 15 weeks of either (1) high‐intensity swimming (HIS, n = 21), (2) moderate‐intensity swimming (MOD, n = 21) or (3) control (CON, n = 20). Training s...

Short-term heat acclimation (HA) appears adequate for maximizing sudomotor adaptations and enhancing thermal resilience in trained athletes. However, for enhanced erythropoiesis and transfer effects to exercise capacity in cooler environments, prolonged HA appears necessary. To establish the time-course for physiological adaptations and performance...

Purpose To investigate the impact of soccer training on cardiac adaptations in mildly hypertensive middle-aged women. Methods Hypertensive premenopausal women (n = 41; age (mean ± SD): 44 ± 7 years; height: 166 ± 6 cm; weight: 78.6 ± 11.6 kg; body fat: 43.3 ± 5.2%) were randomized to soccer training (SOC, n = 21) or control (CON, n = 20). SOC perf...

Systematic exercise training effectively improves exercise capacity in patients with coronary artery disease (CAD), but the magnitude of improvements is highly heterogeneous. We investigated whether this heterogeneity in exercise capacity gains is influenced by the insertion/deletion (I/D) polymorphism of the angiotensin-converting enzyme (ACE) gen...

Background: Serum INSL3 is a Leydig cell biomarker, but little is known about the circulating concentration of INSL3 during hypothalamus-pituitary-testicular suppression. Aim: To study the concomitant changes in serum concentrations of INSL3, testosterone and LH during experimental and therapeutic testicular suppression. Methods: We included s...

Objectives To investigate whether recombinant human erythropoietin (rHuEPO) injections during an altitude training camp impact heart function. Methods Thirty (12 women) moderately trained subjects stayed at 2320 m altitude for 4 weeks while training. Subjects were randomized to placebo (isotonic saline) or rHuEPO (20 IU/kg body weight) i.v. inject...

Purpose: We investigated the effects of recombinant human erythropoietin (rHuEPO) administration on exercise endurance, maximal aerobic performance and total hemoglobin mass (tHb). We hypothesized that frequent, small intravenous injections of epoetin β would increase time trial performance, peak oxygen uptake (V̇O2peak) and tHb in both males and...

Purpose Angiotensin-converting enzyme (ACE) inhibitor treatment is widely applied, but the fact that plasma ACE activity is a potential determinant of training-induced local muscular adaptability is often neglected. Thus, we investigated the hypothesis that ACE inhibition modulates the response to systematic aerobic exercise training on leg and arm...

Angiotensin-converting enzyme (ACE) activity may be one determinant of adaptability to exercise training, but well-controlled studies in humans without confounding conditions are lacking. Thus, the purpose of the present study was to investigate whether ACE inhibition affects cardiovascular adaptations to exercise training in healthy humans. Health...

Dried blood spot (DBS) testing allows fast, easy, and minimally invasive collection of microvolumes of blood. In an anti‐doping context, DBS testing has particular relevance for substances prohibited in‐competition only such as ephedrine, which is currently detected by urine analysis, since DBS can add information about the blood drug concentration...

The World Anti‐Doping Agency prohibit glucocorticoid (GC) administration during competition but allow administration in periods out of competition. However, GC administration may accelerate erythropoiesis and resemble blood volume manipulation methods, which are prohibited at all times. Here, we investigated whether a single GC injection accelerate...

Objectives To investigate whether recombinant human erythropoietin (rHuEPO) injections during an altitude training camp impact heart function. Methods Thirty-nine (16 women) moderately trained subjects stayed at 2,320 m altitude for 4 weeks while training. Subjects were randomized to placebo (isotonic saline) or rHuEPO (20 IU/kg body weight) i.v....

The erythroid terminal differentiation program couples sequential cell divisions with progressive reductions in cell size. The erythropoietin receptor (EpoR) is essential for erythroblast survival, but its other functions are not well characterized. Here we use Epor −/− mouse erythroblasts endowed with survival signaling to identify novel non-redun...

The SHFT device is a novel running wearable consisting of two pods connected to your smartphone issuing several running metrics based on accelerometer and gyroscope technology. The purpose of this study was to investigate the reliability and validity of the power output (PO) metric produced by the SHFT device. To assess reliability, 12 men ran on a...

Erythroid terminal differentiation (ETD) entails cell divisions coupled to decreasing cell size. The tight link between the number of cell divisions and red cell size is apparent in nutritional deficiencies or genetic variants in which fewer cycles result in larger red cells. Here we investigated novel EpoR functions, finding that EpoR signaling di...

Exercise facilitates cerebral lactate uptake, likely by increasing arterial lactate concentration and hence the diffusion gradient across the blood brain barrier. However, non-specific β-adrenergic blockade by propranolol has previously reduced the arterio-jugular venous lactate difference (AV Lac ) during exercise, suggesting β-adrenergic control...

Objectives The agro-pastoralist Maasai of East Africa are highly physically active, but their aerobic fitness has so far only been estimated using heart rate (HR) response to submaximal exercise and not directly measured. Thus, we aimed to measure aerobic fitness directly using respiratory gas analysis in a group of Maasai, and habitual physical ac...

Background The aim of this study was to examine feasibility of trial processes and group-based, structured exercise training in patients with first-episode psychosis. Methods Twenty-five patients with first-episode psychosis took part in a two-arm randomised feasibility trial. They were individually randomised (1:1) via a computer-generated random...

This study aimed to determine and compare the perception, painfulness, and usability of the minimally invasive Dried Blood Spot (DBS) collections from fingertip vs. upper arm from different athlete populations: males and females representing sports dependent on hand/arm, sports less dependent on hand/arm and para‐athletes. To accomplish this, 108 n...

Our aim was to provide an in vivo assessment of human muscle twitch characteristics during and following an exhaustive dynamic exercise to explore temporal alterations of the rate of force development (RFD) and relaxation (RFR). Eleven healthy participants (mean age ± SD: 24 ± 3 years) completed a dynamic knee-extensor exercise in randomized order...

Current markers of iron deficiency (ID) such as ferritin and hemoglobin have shortcomings, and hepcidin and erythroferrone (ERFE) could be of clinical relevance in relation to early assessment of ID. Here, we evaluate whether exposure to altitude-induced hypoxia (2,320 m) alone, or in combination with recombinant human erythropoietin (rHuEPO) treat...

We investigated whether immature reticulocyte fraction (IRF) and immature reticulocytes to red blood cells ratio (IR/RBC) are sensitive biomarkers for low-dose recombinant human erythropoietin (rhEpo) treatment at sea-level (SL) and moderate altitude (AL) and whether multi (FACS) or single (Sysmex-XN) fluorescence flow cytometry is superior for IRF...

While misuse of testosterone esters is widespread in elite and recreational sports, direct detection of intact testosterone esters in doping control samples is hampered by the rapid hydrolysis by esterases present in the blood. With dried blood spot (DBS) as sample matrix, continued degradation of the esters is avoided due to inactivation of the hy...

Background To examine feasibility of trial processes and group-based, structured exercise training in patients with first-episode psychosis (FEP).Methods Twenty-five patients with FEP took part in a two-arm randomised feasibility trial. Patients were individually randomised (1:1) via a computer-generated randomisation sequence and allocated to eith...

We evaluated the cardiometabolic effects of a 15-week combined exercise programme, implemented in sports clubs, for 50–70-year-olds with low aerobic fitness. In a randomized controlled trial, 45 participants (26 women) with low fitness were randomly assigned (2:1-ratio) to a training group (TG, n = 30) or inactive control group (CG, n = 15). TG had...

We examined the application of a land-based swimming ergometer 3-min all-out test to determine physiological predictors of swimming performance. Fourteen young elite swimmers participated (males: n=6; females: n=8). The swimmers completed two 3-min upper-body all-out tests on a swimming ergometer. Additionally, the swimmers completed freestyle swim...

Erythroid terminal differentiation entails cell divisions that are coupled to progressive decreases in cell size. EpoR signaling is essential for the survival of erythroid precursors, but it is unclear whether it has other functions in these cells. Here we endowed mouse precursors that lack the EpoR with survival signaling, finding that this was su...

Erythroid terminal differentiation entails cell divisions that are coupled to progressive decreases in cell size. EpoR signaling is essential for the survival of erythroid precursors, but it is unclear whether it has other functions in these cells. Here we endowed mouse precursors that lack the EpoR with survival signaling, finding that this was su...

Objective Several working groups (eg, miners, flight crews and soldiers) are subjected to chronic intermittent hypoxic exposure. The cardiovascular implications have been studied but not systematically reviewed with focus on possible negative health implications. The aim of the present review was to systematically evaluate the hypothesis that inter...

Sprint-interval training (SIT) is efficient at improving maximal aerobic capacity and anaerobic fitness at sea-level and may be a feasible training strategy at altitude. Here, it was evaluated if SIT intensity can be maintained in mild to moderate hypoxia. It was hypothesized that 6 x 30 s Wingate sprint performance with 2 min active rest between s...

Objectives: To evaluate whether the donation of 900 mL of blood reduces the central blood volume (CBV) assessed by thoracic electrical impedance (TI) and plasma pro-atrial natriuretic peptide (proANP). Background: Donation of 450 mL of blood carries a 1% risk of a vasovagal reaction. Withdrawal of 900 mL of blood decreases cardiac output; howeve...

Purpose: Limited data are available on the acute performance-enhancing effects of single-dose administration of testosterone in healthy humans. Studies of testosterone administrations to healthy humans are rare due to the difficult nature and necessity of close clinical monitoring. However, our unique physiological experimental facilities combined...

This study evaluated whether recombinant human erythropoietin (rhEpo) treatment combined with chronic hypoxia provided an additive erythropoietic response and whether the athlete biological passport (ABP) sensitivity improved with hypoxia. Two interventions were completed, each containing 4 weeks baseline, 4 weeks exposure at sea level or 2,320 m o...

Total hemoglobin mass (Hbmass) is routinely assessed in studies by the carbon monoxide (CO) rebreathing. Its clinical application is often hindered due to the consequent rise in carboxyhemoglobin (%HbCO) and the concern of CO toxicity. We tested the reproducibility of the CO rebreathing with a CO dose of 0.5 mL/kg body mass (CO0.5) compared to 1.5...

Objectives Optimized concurrent training regimes are warranted in physical training of military-, law enforcement- and rescue-personnel. This study investigated if four 15-min endurance training sessions weekly improve aerobic capacity and performance more than one 60-min endurance session weekly during the initial phase of a Basic Military Trainin...

EpoR signaling is essential for the survival of erythroid precursors during terminal differentiation, when these cells undergo 3-5 cell divisions that are coupled to a rapid loss in cell size. The absolute dependence of erythroblasts on EpoR signaling for survival makes it challenging to identify other essential functions of EpoR in these cells. Ke...

Purpose: Autologous blood transfusion is performance enhancing and prohibited in sport but remains difficult to detect. This study explored the hypothesis that an untargeted urine metabolomics analysis can reveal one or more novel metabolites with high sensitivity and specificity for detection of autologous blood transfusion. Methods: In a rando...

Clenbuterol is a β2‐agonist prescribed for asthmatic patients in some countries. Based on its anabolic and lipolytic effects observed in studies on rodents and in livestock destined for food production, clenbuterol is abused by bodybuilders and athletes seeking leanness. Urinary clenbuterol analysis is part of routine doping analysis. However, the...

Testosterone treatment stimulates red blood cell production and alters iron homeostasis. Thus, we investigated whether the ‘hematological module’ of the Athlete Biological Passport (ABP) used by the World Anti‐Doping Agency (WADA) can be used to indicate misuse of testosterone. Nineteen eugonadal men received intramuscular injections of either 250...

Objectives Military-, rescue- and law-enforcement personnel require a high physical capacity including muscular strength. The present study hypothesized that 9 weeks of volume matched concurrent short frequent training sessions increases strength more efficiently than less frequent longer training sessions. Design A randomized training interventio...

Autologous blood transfusion (ABT) is illegal for competing athletes but misuse remains difficult to detect. Thus, the development of novel and sensitive methods is warranted. In this study, we explored whether ABT causes a shift of the urine metabolome. The hypothesis was that an untargeted metabolomics analysis of urine is able to identify novel...

Clenbuterol is a beta2 -adrenoceptor agonist marketed as an asthma reliever but is not approved for human use in most countries due to concerns of adverse cardiac effects. Given its demonstrated hypertrophic and lipolytic actions in rodents, clenbuterol is one of the most widely abused doping substances amongst athletes and recreational body-builde...

Purpose: To investigate the hypothesis that a therapeutic oral dose of Tramadol improves cycling time trial performance and compromises motor-cognitive performance in highly trained cyclists. Methods: Following two familiarization trials, 16 highly trained cyclists completed a preloaded time trial (1 hour at 60 % of peak power followed by a 15 k...

The main objective of this work was to investigate whether mitochondrial fusion occurs in the skeletal muscle of well‐trained athletes in response to high‐intensity exercise. Well‐trained swimmers (n = 9) performed a duration‐matched sprint interval training (SIT) and high‐intensity high‐volume training (HIHVT) session on separate days. Muscle samp...

This review critically evaluates the magnitude of performance enhancement that can be expected from various autologous blood transfusion (ABT) procedures and the underlying physiological mechanisms. The review is based on a systematic search, and it was reported that 4 of 28 studies can be considered of very high quality, i.e. placebo-controlled, d...

Background: Burgeoning evidence suggests that exercise improves physical and mental health in people with schizophrenia. However, little is known about the feasibility and acceptability of high-intensity training in patients with first-episode psychosis. This qualitative study explored motivation, social interaction and experiences of participants...

Purpose: To develop and validate a novel model for assessment of peripheral fatigue progression during dynamic exercise. Methods: Seven males and four females (24 ± 3 yr) completed one-legged knee-extensor exercise at 40% of peak power output (PPO) for 12 min (40% PPO). Additionally, an exhaustive bout lasting approximately 6 min (84% ± 2% PPO;...

Detailed physiological phenotyping was hypothesized to have predictive value for Olympic distance cross-country mountain bike (XCO-MTB) performance. Additionally, mean (MPO) and peak power output (PPO) in 4 × 30 s all-out sprinting separated by 1 min was hypothesized as a simple measure with predictive value for XCO-MTB performance. Parameters indi...

Purpose: This study tested the hypothesis that autologous blood transfusion (ABT) of ~50% of the red blood cells (RBCs) from a standard 450 ml phlebotomy would increase mean power in a cycling time trial. Additionally, the study investigated whether further ABT of RBCs obtained from another 450 ml phlebotomy would increase repeated cycling sprint...

Background The performance of elite breath hold divers (BHD) includes static breath hold for more than 11 minutes, swimming as far as 300 m, or going below 250 m in depth, all on a single breath of air. Diving mammals are adapted to sustain oxidative metabolism in hypoxic conditions through several metabolic adaptations, including improved capacity...

This study examined to what extent the human cerebral and femoral circulation contribute to free radical formation during basal and exercise-induced responses to hypoxia. Healthy participants (5♂, 5♀) were randomly assigned single-blinded to normoxic (21% O2) and hypoxic (10% O2) trials with measurements taken at rest and 30min after cycling at 70%...

The novel hypothesis that "Live High-Train Low" (LHTL) does not improve sport-specific exercise performance (e.g., time trial) is discussed. Indeed, many studies demonstrate improved performance after LHTL but unfortunately control groups are often lacking, leaving open the possibility of training camp effects. Importantly, when control groups, bli...

Purpose: To examine the skeletal muscle and performance responses across two different exercise training modalities which are highly applied in soccer training. Methods: Using an RCT design, 39 well-trained male soccer players were randomized into either a speed endurance training (SET; n = 21) or a small-sided game group (SSG; n = 18). Over 4 w...

It was investigated, if a newly developed discipline specific test for elite-level trapeze sailors is reli-able and sensitive. Furthermore, the physical demands of trapeze sailing were examined. In part 1, nine national team athletes were accustomed to a simulated sailing test, which subsequently was completed on four occasions to determine test re...

We aimed to test whether high-intensity high-volume training (HIHVT) swimming would induce more robust signaling than sprint interval training (SIT) swimming within the m. triceps brachii due to lower metabolic and oxidation. Nine well-trained swimmers performed the two training procedures on separate randomized days. Muscle biopsies from m. tricep...

Purpose: It was investigated if β-alanine supplementation counteracts muscular fatigue development or improves athletic performance. Methods: Elite kayak rowers (10 males and 7 females) were supplemented with either 80 mg/kg body mass/day β-alanine or placebo for 8 weeks. Muscular fatigue development was investigated by applying a 2 min elbow fl...

It was evaluated whether upper-body compared to lower-body musculature exhibits a different phenotype in relation to capacity for handling reactive oxygen species (ROS), H+, La−, Na+, K+ and also whether it differs in adaptive potential to exercise training. Eighty-three sedentary premenopausal women aged 45 ± 6 years (mean ± SD) were randomized in...

A 1% change in average speed is enough to affect medal rankings in intense Olympic endurance events lasting ~45 s to 8 min which for example includes 100 m swimming and 400 m running (~1 min), 1,500 m running and 4000 m track cycling (~4 min) and 2,000 m rowing (~6-8 min). To maximize the likelihood of winning, athletes utilizes legal supplements w...

The aim was to investigate whether 6 weeks of normobaric “Live High-Train Low” (LHTL) using altitude tents affect highly trained athletes incremental peak power, 26-km time-trial cycling performance, 3-min all-out performance, and 30-s repeated sprint ability. In a double-blinded, placebo-controlled cross-over design, seven highly trained triathlet...

Valid assessments of physical activity (PA) and cardiorespiratory fitness (CRF) is essential in epidemiological studies to define dose-response relationship for e.g. formulating thorough recommendations of an appropriate pattern of PA to maintain good health. The aim of this study was to validate the Danish step test, the physical activity question...

The time course of plasma volume (PV) reduction following an increased training load period is unknown and was investigated. The accompanying fluctuations in [Hb] and OFF-hr score were analyzed in the Athlete Biological Passport. Further, whether fluctuations in plasma albumin, soluble transferrin receptors (sTfR), and pro-atrial natriuretic peptid...

The hypothesis, that sailing upwind in wind speeds above 12 knots causes fatigue, which manifests as a reduction in exerted hiking strap force and/or maximal isometric voluntary contraction force (MVC) of the knee extensors, was evaluated. Additionally, it was investigated if a relationship exists between maximal exerted hiking force (hMVC) and sai...

Purpose: The aim of the present study was to investigate the influence of futsal match-related fatigue on running performance, neuromuscular variables, and finishing kick speed and accuracy. Methods: Ten professional futsal players participated in the study (age: 22.2 ± 2.5 years) and initially performed an incremental protocol to determine maximum...

Purpose: We tested the hypothesis that low-volume high-intensity swimming has a larger impact on insulin sensitivity and glucose control than high-volume low-intensity swimming in inactive premenopausal women with mild hypertension. Methods: Sixty-two untrained premenopausal women were randomised to an inactive control (n = 20; CON), a high-inte...

To minimize the chances of being caught after doping with recombinant human erythropoietins (rhEPO), athletes have turned to new practices using micro-doses and excess fluid ingestion to accelerate elimination and decrease the probability of detection. Our objective was to test the sensitivity of detection by validated methods (IEF: isoelectric foc...

The nutritional supplement (NS) industry is one of the fastest growing in the world, and NS use in Denmark is among the highest in Europe. However, the exact use in elite athletes and fitness customers targeted for doping control is unknown. Information from 634 doping control forms obtained in 2014 was evaluated (elite athletes: n = 361; fitness c...