S P Magnusson

IT University of Copenhagen, København, Capital Region, Denmark

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Publications (192)593.88 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The musculoskeletal system and its connective tissue include the intramuscular connective tissue, the myotendinous junction, the tendon, the joints with their cartilage and ligaments, and the bone; they all together play a crucial role in maintaining the architecture of the skeletal muscle, ensuring force transmission, storing energy, protecting joint surface and stability, and ensuring the transfer of muscular forces into resulting limb movement. The musculoskeletal connective tissue structure is relatively stable, but mechanical loading and subsequent mechanotransduction and molecular anabolic signaling can result in some adaptation of the connective tissue, its size, its strength, and its mechanical properties, whereby it can improve its capacity by 5-20% with regular physical activity. For several of the mechanically loaded connective tissues, only limited information regarding molecular and cellular signaling pathways and their adaptation to exercise is available. In contrast to tissue responses with exercise, lack of mechanical tissue loading through inactivity or immobilization of the human body will result in a dramatic loss of connective tissue content, structure, and tolerable load within weeks, to a degree (30-40%) that mimics that of contractile skeletal musculature. This illustrates the importance of regular mechanical load in order to preserve the stabilizing role of the connective tissue for the overall function of the musculoskeletal system in both daily activity and exercise.
    No preview · Chapter · Dec 2015
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    ABSTRACT: Diabetic patients have an increased risk of foot ulcers, and glycation of collagen may increase tissue stiffness. We hypothesized that the level of glycemic control (glycation) may affect Achilles tendon stiffness, which can influence gait pattern. We therefore investigated the relationship between collagen glycation, Achilles tendon stiffness parameters and plantar pressure in poorly (n = 22) and well (n = 22) controlled diabetic patients, including healthy age matched (45-70 yrs) controls (n = 11). There were no differences in any of outcome parameters (collagen cross-linking or tendon stiffness) between patients with well-controlled and poorly controlled diabetes. The overall effect of diabetes was explored by collapsing the diabetes groups (DB) compared to the controls. Skin collagen cross-linking lysylpyridinoline (LP), hydroxylysylpyridinoline (HP), (136%, 80%, P < 0.01) and pentosidine concentrations (55%, P < 0.05) were markedly greater in DB. Furthermore, Achilles tendon material stiffness was higher in DB (54%, P < 0.01). Notably, DB also demonstrated higher forefoot/ rearfoot peak plantar pressure (PPP)-ratio (33%, P < 0.01). Overall, Achilles tendon material stiffness and skin connective tissue cross-linking were greater in diabetic patients compared to controls. The higher foot pressure indicates that material stiffness of tendon and other tissue (e.g skin and joint capsule) may influence on foot gait. The difference in foot pressure distribution may contribute to the development of foot ulcers in diabetic patients.
    Full-text · Article · Nov 2015 · Journal of Applied Physiology
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    ABSTRACT: Synopsis Tendinopathy is a very common disorder in both recreational and elite athletes. Many individuals have recurrent symptoms that lead to chronic conditions and termination of sports activity. Exercise has become a popular and somewhat efficacious treatment regime, and in particular isolated eccentric exercise has been promoted. In this review we cover the relevant evidence for different exercise regimes in tendinopathy rehabilitation with particular focus on the applied loads that are experienced by the tendon and how the exercise regime may affect these applied loads. There is no convincing clinical evidence that demonstrate that isolated eccentric loading exercises improve the clinical outcome more than other loading therapies. However, the great variation and sometimes insufficient reporting of details of treatment protocols hamper the interpretation of what may be the optimal exercise regime with respect to parameters like load magnitude, speed of movement, and recovery period between exercise sessions. Future studies should control for these loading parameters, evaluate various exercise dosages, and also think beyond isolated eccentric exercises to arrive at firm recommendations regarding rehabilitation of individuals with tendinopathies. J Orthop Sports Phys Ther, Epub 15 Oct 2015. doi:10.2519/jospt.2015.5910.
    Full-text · Article · Oct 2015
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    ABSTRACT: Diabetes is a major risk factor for tendinopathy and tendon abnormalities are common in diabetic patients. The purpose of this study was to evaluate the effect of streptozotocin-induced (STZ, 60 mg⋅kg(-1)) diabetes and insulin therapy on tendon mechanical and cellular properties. Sprague Dawley rats (n=40) were divided into four groups: non-diabetic (Control), 1-week of diabetes (Acute), 10 weeks of diabetes (Chronic), 10 weeks of diabetes with insulin (Insulin). After ten weeks Achilles tendon and tail fascicle mechanical properties were similar between groups (p>0.05). Cell density in the Achilles was greater in the Chronic group when compared to Control and Acute (p<0.05, Control: 7.8±0.5, Acute: 8.3±0.4, Chronic: 10.9±0.9, Insulin: 9.2±0.8 cells/100 μm(2)). The density of proliferating cells in the Achilles was greater in the Chronic group when compared to all other groups (p<0.05, Control: 0.025±0.009, Acute: 0.019±0.005, Chronic: 0.067±0.015, Insulin: 0.004±0.004 cells/100 μm(2)). Patellar tendon collagen content was ~32% greater in the Chronic and Acute groups when compared to Control or Insulin (p<0.05, Control: 681±63, Acute: 938±21, Chronic: 951±52, Insulin: 596±84 μg collagen⋅mg dry weight(-1)). In contrast, patellar tendon hydroxylysyl pyridinoline cross-linking and collagen fibril organization were unchanged by diabetes or insulin (p>0.05). Our findings suggest that 10 weeks of STZ-induced diabetes does not alter rat tendon mechanical properties even with an increase in collagen content. Future studies could attempt to further address the mechanisms contributing to the increase in tendon problems noted in diabetic patients, especially since our data suggest that hyperglycemia per se does not alter tendon mechanical properties. Copyright © 2015, American Journal of Physiology - Regulatory, Integrative and Comparative Physiology.
    No preview · Article · Aug 2015 · AJP Regulatory Integrative and Comparative Physiology
  • Jens Bojsen-Møller · S. Peter Magnusson
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    ABSTRACT: The free Achilles tendon is considered a homogenous structure that transmits muscular force in a linear manner. However, the tendon undergoes longitudinal rotation and is separated in mechanically independent segments with distinct mechanical and material tissue properties. The present review examines the hypothesis that the human Achilles tendon is asymmetrically loaded, and undergoes heterogeneous deformation during movement. The present review examines the hypothesis that the Achilles tendon is asymmetrically loaded, and undergoes heterogeneous deformation during human movement.
    No preview · Article · Jul 2015 · Exercise and sport sciences reviews
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    ABSTRACT: Previous studies have shown that eccentric training has a positive effect on Achilles tendinopathy, but few randomized controlled trials have compared it with other loading-based treatment regimens. To evaluate the effectiveness of eccentric training (ECC) and heavy slow resistance training (HSR) among patients with midportion Achilles tendinopathy. Randomized controlled trial; Level of evidence, 1. A total of 58 patients with chronic (>3 months) midportion Achilles tendinopathy were randomized to ECC or HSR for 12 weeks. Function and symptoms (Victorian Institute of Sports Assessment-Achilles), tendon pain during activity (visual analog scale), tendon swelling, tendon neovascularization, and treatment satisfaction were assessed at 0 and 12 weeks and at the 52-week follow-up. Analyses were performed on an intention-to-treat basis. Both groups showed significant (P < .0001) improvements in Victorian Institute of Sports Assessment-Achilles and visual analog scale from 0 to 12 weeks, and these improvements were maintained at the 52-week follow-up. Concomitant with the clinical improvement, there was a significant reduction in tendon thickness and neovascularization. None of these robust clinical and structural improvements differed between the ECC and HSR groups. However, patient satisfaction tended to be greater after 12 weeks with HSR (100%) than with ECC (80%; P = .052) but not after 52 weeks (HSR, 96%; ECC, 76%; P = .10), and the mean training session compliance rate was 78% in the ECC group and 92% in the HSR group, with a significant difference between groups (P < .005). The results of this study show that both traditional ECC and HSR yield positive, equally good, lasting clinical results in patients with Achilles tendinopathy and that the latter tends to be associated with greater patient satisfaction after 12 weeks but not after 52 weeks. © 2015 The Author(s).
    No preview · Article · May 2015 · The American Journal of Sports Medicine
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    ABSTRACT: Lysyl oxidases (LOXs) are a family of copper- dependent oxido-deaminases that can modify the side-chain of lysyl residues in collagen and elastin, thereby leading to the spontaneous formation of non-reducible aldehyde-derived inter-polypeptide chain cross-links. The consequences of LOX inhibition in producing lathyrism are well documented but the consequences on collagen fibril formation are less clear. Here we used β-aminoproprionitrile (BAPN) to inhibit LOX in tendon-like constructs (prepared from human tenocytes), which are an experimental model of cell- mediated collagen fibril formation. The improvement in structure and strength seen with time in control constructs was absent in constructs treated with BAPN. As expected, BAPN inhibited the formation of aldimine- derived cross-links in collagen and the constructs were mechanically weak. However, an unexpected finding was that BAPN- treatment led to structurally abnormal collagen fibrils with irregular profiles and widely dispersed diameters. Of special interest, the abnormal fibril profiles resembled those seen in some Ehlers-Danlos Syndrome (EDS) phenotypes. Importantly, the total collagen content developed normally, and there was no difference in COL1A1 gene expression. Collagen type V , decorin, fibromodulin and tenascin-X proteins were unaffected by the cross-link inhibition, suggesting that LOX regulates fibrillogenesis independently of these molecules. Collectively, the data show the importance of LOX on the mechanical development of early collagenous tissues, and that LOX is essential for correct collagen fibril shape formation. Copyright © 2015, The American Society for Biochemistry and Molecular Biology.
    No preview · Article · May 2015 · Journal of Biological Chemistry
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    ABSTRACT: We examined whether diastolic left ventricular function in young and senior life-long endurance-runners was significantly different from sedentary age-matched controls, and if life-long endurance running appears to modify the age related decline in diastolic left ventricular function. The study comprised 17 senior athletes (age: 59-75 years, running distance: 30-70 km/week), 10 young athletes (age: 20-36 years, matched for running distance), 11 senior and 12 young weight-matched sedentary controls. Peak early (E) and late (A) mitral inflow and early (e') and late (a') diastolic and systolic (s') annular longitudinal tissue Doppler velocities were measured by echocardiography during four stages (rest, supine bike exercise at 30% and 60% of maximal workload, and recovery). Athletes had marked cardiac remodelling, while overall differences in mitral inflow and annular tissue Doppler velocities during rest and exercise were more associated with age than training status. Senior participants had lower E/A at rest, overall lower E, e' and s', and greater E/e' compared to the young (all P<0.05). Athletes had greater E/A (P=0.004), but tissue Doppler velocities were not different from controls. Life-long endurance running was not associated with major attenuation of the age-related decline in diastolic function at rest or during exercise.
    No preview · Article · May 2015 · Scandinavian cardiovascular journal: SCJ
  • L. Hansen · K. Erhardsen · J. Bencke · S.P. Magnusson · D.J. Curtis

    No preview · Article · May 2015 · Physiotherapy
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    S. S. Balle · S. P. Magnusson · M. P. McHugh
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    ABSTRACT: The purpose of this study was to determine the acute effects of contract-relax stretching (CRS) vs static stretching (SS) on strength loss and the length-tension relationship. We hypothesized that there would be a greater muscle length-specific effect of CRS vs SS. Isometric hamstring strength was measured in 20 healthy people at four knee joint angles (90°, 70°, 50°, 30°) before and after stretching. One leg received SS, the contralateral received CRS. Both stretching techniques resulted in significant strength loss, which was most apparent at short muscle lengths [SS: P = 0.025; stretching × angle P < 0.001; 11.7% at 90° P < 0.01; 5.6% at 70° nonsignificant (ns); 1.3% at 50° ns; −3.7% at 30° ns. CRS: P < 0.001; stretching × angle P < 0.001; 17.7% at 90°, 13.4% at 70°, 11.4% at 50°, all P < 0.01, 4.3% at 30° ns]. The overall stretch-induced strength loss was greater (P = 0.015) after CRS (11.7%) vs SS (3.7%). The muscle length effect on strength loss was not different between CRS and SS (stretching × angle × stretching technique P = 0.43). Contrary to the hypothesis, CRS did not result in a greater shift in the length–tension relationship, and in fact, resulted in greater overall strength loss compared with SS. These results support the use of SS for stretching the hamstrings.
    Full-text · Article · Feb 2015 · Scandinavian Journal of Medicine and Science in Sports
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    ABSTRACT: tendon and skeletal muscle function adapts to physical training of resistive nature, but it is unknown to what extent persons with genetically altered connective tissue - who have a higher than normal tendon extensibility - will obtain any effect upon their tendon and muscle when undergoing muscle strength training. We investigated patients with classical Ehlers Danlos Syndrome (EDS) (collagen type V defect) who display articular hypermobility, skin extensibility and tissue fragility. subjects underwent strength training 3 times a week for 4 months and were tested before and after intervention in regards to muscle strength, tendon mechanical properties, and muscle function. three subjects completed the scheduled 48 sessions and had no major adverse events. Mean isometric leg extension force and leg extensor power both increased by 8 and 11% respectively (358 to 397 N, and 117 to 123 W). The tendon stiffness was tested and an average increase in response to physical training, from 1795 to 2519 N/mm was found. On average, the training loads both in upper and lower body exercises increased by around 30% over the training period. When testing balance, the average sway-area of the participants decreased by 26% (0.144 to 0.108 m(2)). On the subscale of CIS20 the participants lowered their average subjective fatigue score from 33 to 25. in this small pilot study, heavy resistance training was both feasible and effective in classic Ehlers Danlos patients, and the results indicated that both tendon and skeletal muscle properties can be improved also in this patient group when they are subjected to resistance training.
    No preview · Article · Dec 2014 · Muscles
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    ABSTRACT: In the past twenty years, the use of ultrasound-based methods has become a standard approach to measure tendon mechanical properties in vivo. Yet, the multitude of methodological approaches adopted by various research groups probably contributes to the large variability of reported values. The technique of obtaining and relating tendon deformation to tensile force in vivo has been applied differently, depending on practical constraints or scientific points of view. Divergence can be seen in i) methodological considerations such as the choice of anatomical features to scan and to track, force measurements or signal synchronisation and ii), in physiological considerations related to the viscoelastic behaviour or length measurements of tendons. Hence, the purpose of the present review is to assess and discuss the physiological and technical aspects connected to in vivo testing of tendon mechanical properties. In doing so, our aim is to provide the reader with a systematic, qualitative analysis of ultrasound-based techniques. Finally, a list of recommendations is proposed for a number of selected issues. Copyright © 2014, Journal of Applied Physiology.
    No preview · Article · Nov 2014 · Journal of Applied Physiology
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    ABSTRACT: (1) Objective Isolated human tendon cells form 3D tendon constructs that demonstrate collagen fibrillogenesis and feature structural similarities to tendon when cultured under tensile load. The exact role of circulating growth factors for collagen formation in tendon is sparsely examined. We investigated the influence of insulin-like growth factor I (IGF-I) on tendon construct formation in 3D cell culture. (2) Design Tendon constructs were grown in 0.5 or 10% FBS with or without IGF-I (250 mg/ml) supplementation. Collagen content (fluorometric), mRNA levels (PCR) and fibril diameter (transmission electron microscopy) were determined at 7, 10, 14, 21 and 28 days. (3) Results IGF-I revealed a stimulating effect on fibril diameter (up to day 21), mRNA for collagen (to day 28), tenomodulin (to day 28) and scleraxis (at days 10 and 14), and on overall collagen content. 10% FBS diminished the development of fibril diameter (day 14), collagen content (at days 21 and 28), and mRNA expression for collagen, tenomodulin and scleraxis. (4) Conclusion IGF-I supplementation promotes early onset of tensile load induced collagen formation and tendon structural arrangement, whereas the FBS concentration routinely used in cultures diminishes collagen expression, collagen content and fibril formation.
    No preview · Article · Sep 2014 · Growth Hormone & IGF Research
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    ABSTRACT: There is a clinical overlap between classic Ehlers-Danlos syndrome (cEDS) and benign joint hypermobility syndrome (BJHS), with hypermobility as the main symptom. The purpose of this study was to investigate the role of type V collagen mutations and tendon pathology in these 2 syndromes. In patients (cEDS, n=7; BJHS, n=8) and controls (Ctrl, n=8), we measured patellar tendon ultrastructure (transmission electron microscopy), dimensions (magnetic resonance imaging), and biomechanical properties (force and ultrasonographic measurements during a ramped isometric knee extension). Mutation analyses (COL5A1 and COL5A2) were performed in the patients. COL5A1 mutations were found in 3 of 4 of the patients with cEDS. Patellar tendon dimensions were similar between the groups, but large, irregular collagen fibrils were in 4 of 5 patients with cEDS. In the cEDS group, tendon stiffness and Young's modulus were reduced to ∼50% of that in BJHS and Ctrl groups (P<0.05). The nonhypermobile, healthy controls were matched with the patients in age, sex, body weight, and physical activity, to compare outcomes. COL5A1 mutations led to structural tendon pathology and low tendon stiffness in cEDS, explaining the patients' hypermobility, whereas no tendon pathology was found that explained the hypermobility in BJHS.-Nielsen, R. H., Couppé, C., Jensen, J. K., Olsen, M. R., Heinemeier, K. M., Malfait, F., Symoens, S., De Paepe, A., Schjerling, P., Magnusson, S. P., Remvig, L., Kjaer, M. Low tendon stiffness and abnormal ultrastructure distinguish classic Ehlers-Danlos syndrome from benign joint hypermobility syndrome in patients.
    Full-text · Article · Aug 2014 · The FASEB Journal
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    ABSTRACT: Tendon pathology is related to metabolic disease and mechanical overloading, but the effect of metabolic disease on tendon mechanics is unknown. This study investigated the effect of diet and apolipoprotein E deficiency (ApoE(-/-)) on the mechanical properties and advanced glycation end products (AGEs) cross-linking of non-weight bearing mouse tail tendons. Twenty ApoE(-/-) male mice were used as a model for hypercholesterolemia along with 26 wild-type (WT). Half of the mice from each group were fed a normal diet (ND) and the other half was fed high fat diet (HFD) to induce obesity. All were sacrificed at 40 weeks and tail tendon fascicles were mechanically tested to failure and analyzed for AGEs. Diets were also analyzed for AGEs. ApoE(-/-) mice displayed 14% increase in plateau modulus compared to WT mice (p<0.05), while HFD mice displayed 13 % decrease in plateau modulus (p<0.05) and 12% decrease in total modulus (p<0.05) compared to ND mice. Tail tendons of HFD mice had significantly lower concentrations of AGEs (CML: 26%, p<0.0001, MG-H1: 15%, p<0.005, pentosidine: 13%, p<0.0005). The HFD had ∼ 44 fold lower content of CML (p < 0.01), ∼ 29 fold lower content of CEL (p < 0.005), and ∼ 16 fold lower content of MG-H1 (p < 0.05) compared to ND. ApoE(-/-) increased whereas HFD decreased mouse tail tendon stiffness. Dietary AGE content may be a crucial determinant for accumulation of AGE cross-links in tendons and for tissue compliance. The results demonstrate how systemic metabolic factors may influence tendon health.
    Full-text · Article · Aug 2014 · Journal of Applied Physiology
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    Theresa Bieler · S Peter Magnusson · Michael Kjaer · Nina Beyer
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    ABSTRACT: Objective: To investigate the reliability and agreement of measures of lower extremity muscle strength, power and functional performance in patients with hip osteoarthritis at different time intervals, and to compare these with the same measures in healthy peers. Design: Intra-rater test-retest separated by 1, 2, or 2.5 weeks in patients, and 1 week in healthy peers. Subjects: Patients with hip osteoarthritis (age range 61-83 years) with 1 (n = 37), 2 (n = 35), or 2.5 weeks (n = 15) between tests, and 35 healthy peers (age range 63-82 years). Methods: Maximal isometric hip and thigh strength, leg extensor power, and functional performance (8-foot up and go, stair climbing, chair stand and 6-min walk) were measured in patients, and quadriceps strength, leg extensor power and functional performance were measured in healthy peers. Systematic error, reliability and agreement were calculated. Results: Most hip strength measurements for the most symptomatic extremity, and nearly all strength measurements for the least symptomatic lower extremity, declined after 1 week (p < 0.05), but not after a 2.5-week interval. In healthy peers, quadriceps strength was unchanged. Regardless of the time interval, leg extensor power was unchanged, while functional performances improved at retest for all participants. Conclusion: In patients with hip osteoarthritis leg extensor power is unaffected by the time interval between tests, in contrast to muscle strength and functional performance.
    Preview · Article · Aug 2014 · Journal of Rehabilitation Medicine
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    ABSTRACT: Life-long regular endurance exercise is known to counteract the deterioration of cardiovascular and metabolic function and overall mortality. Yet it remains unknown if life-long regular endurance exercise can influence the connective tissue accumulation of advanced glycation endproducts (AGEs) that is associated with aging and lifestyle-related diseases. We therefore examined two groups of healthy elderly men: 15 master athletes (64 ± 4 years) who had been engaged in life-long endurance running and 12 old untrained (66 ± 4 years) together with two groups of healthy young men; ten young athletes matched for running distance (26 ± 4 years), and 12 young untrained (24 ± 3 years). AGE cross-links (pentosidine) of the patellar tendon were measured biochemically, and in the skin, it was assessed by a fluorometric method. In addition, we determined mechanical properties and microstructure of the patellar tendon. Life-long regular endurance runners (master athletes) had a 21 % lower AGE cross-link density compared to old untrained. Furthermore, both master athletes and young athletes displayed a thicker patellar tendon. These cross-sectional data suggest that life-long regular endurance running can partly counteract the aging process in connective tissue by reducing age-related accumulation of AGEs. This may not only benefit skin and tendon but also other long-lived protein tissues in the body. Furthermore, it appears that endurance running yields tendon tissue hypertrophy that may serve to lower the stress on the tendon and thereby reduce the risk of injury.
    Full-text · Article · Aug 2014 · Journal of the American Aging Association
  • T. Bieler · S. P. Magnusson · M. Kjaer · N. Beyer
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    ABSTRACT: Background Hip osteoarthritis (OA) is a leading cause of pain and functional limitations (1). Current international guidelines recommend exercise as part of the core management for people with Hip OA but the effects of exercise in people with Hip OA are sparsely investigated (2, 3). Objectives In an observer-blinded, randomized trial to compare the effects of 4 months of supervised strength training (ST), supervised Nordic walking (NW), and unsupervised home based exercise (HBE) on functional performance, muscle function, endurance, hip range of motion and self-reported physical function, pain and health related quality of life in people with Hip OA. Methods 60+ years old people with clinical Hip OA (ACR criteria (4)) not on a waiting list for hip replacement were recruited through general practitioners and specialists, and advertisements in local newspapers in Greater Copenhagen. 152 individuals (49 men, 103 women, age 70±6 years) were randomized to ST (n=50), NW (n=50) and HBE (n=52) after baseline assessment. Pre and post assessments were conducted. Physical assessments included 30-second chair stand test (primary outcome), timed stair climbing, 8-foot Up & Go, 15-second marching on the spot, 6-minute walk test, maximal isometric hip and thigh muscle strength and leg extensor power and active hip range of motion. Self-reported outcomes included the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) subscale physical function and pain, and the hip disability and osteoarthritis outcome score (HOOS) subscale hip related quality of life. Results 126 participants completed the 4 months of exercise (ST (n=48), NW (n=35) and HBE (n=43)). The 26 participants who dropped out were characterized by more self-reported symptoms (p<0.05) and higher BMI (p=0.04) at baseline. Both per protocol and intension to treat analyses showed that all groups improved in the primary outcome (p<0.01) with no between-group defferences, while the ST-group had a significantly (p=0.001) greater improvement in self-reported physical function and pain compared to the HBE-group. The NW-group improved significantly (p<0.0001) more in walking distance than the ST-group and the HBE-group. Otherwise, there were no significant differences between the groups. Conclusions All three training modalities resulted in improved chair stand performance. Strength training was superior to home based exercise in improving pain and self-reported physical function while Nordic walking was superior to the other training modalities for improved walking distance in six minutes. References Disclosure of Interest None declared DOI 10.1136/annrheumdis-2014-eular.2360
    No preview · Article · Jun 2014 · Annals of the Rheumatic Diseases
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    ABSTRACT: The objective of this study was to investigate the relative contributions of superficial and deep ankle plantarflexors during repetitive submaximal isometric contractions using surface electromyography (SEMG) and positron emission tomography (PET). Myoelectric signals were obtained from twelve healthy volunteers (27.3 ± 4.2 yrs). A tracer ([18F]-FDG) was injected during the exercise and PET scanning was done immediately afterwards. The examined muscles included soleus (Sol), medial gastrocnemius (MG), lateral gastrocnemius (LG), and flexor hallucis longus (FHL). It was found that isometric maximal voluntary contraction (MVC) force, muscle glucose uptake (GU) rate, and SEMG of various plantarflexors were comparable bilaterally. In terms of%EMG MVC, FHL and MG displayed the highest activity (∼34%), while LG (∼21%) had the lowest activity. Cumulative SEMG from all parts of the triceps surae (TS) muscle accounted for ∼70% of the combined EMG signal of all four plantarflexors. As for GU, the highest quantity was observed in MG (2.4 ± 0.8 μmol∗100g-1∗min-1), whereas FHL (1.8 ± 0.6 μmol∗100g-1∗min-1) had the lowest uptake. Cumulative GU of TS constituted nearly 80% of the combined GU. The findings of this study provide valuable reference for studies where individual muscle contributions are estimated using models and simulations.
    Full-text · Article · Jun 2014 · Journal of electromyography and kinesiology: official journal of the International Society of Electrophysiological Kinesiology
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    ABSTRACT: High-load eccentric exercises have been a key component in the conservative management of chronic Achilles tendinopathy. This study investigated the effects of a 12-week progressive, home-based eccentric rehabilitation program on ankle plantarflexors' glucose uptake (GU) and myoelectric activity, and Achilles tendon GU. A longitudinal study design with control (N = 10) and patient (N = 10) groups was used. Surface electromyography (SEMG) from four ankle plantarflexors and glucose uptake from the same muscles and the Achilles tendon were measured during submaximal intermittent isometric plantarflexion task. The results indicated that the symptomatic leg was weaker (P<0.05) than the asymptomatic leg at baseline but improved (P<0.001) with eccentric rehabilitation. Additionally, the rehabilitation resulted in greater GU in both soleus (P < 0.01) and lateral gastrocnemius (P < 0.001) in the symptomatic leg while the asymptomatic leg displayed higher uptake for medial gastrocnemius and flexor hallucis longus (P<0.05). While both patient legs had higher tendon GU than the controls (P<0.05), there was no rehabilitation effect on the tendon GU. Concerning SEMG, at baseline, soleus showed more relative activity in the symptomatic leg compared to both the asymptomatic and control legs (P<0.05) probably reflecting an effort to compensate for the decreased force potential. The rehabilitation resulted in greater SEMG activity in the lateral gastrocnemius (P<0.01) of the symptomatic leg with no other within- or between-group differences. Eccentric rehabilitation was effective in decreasing subjective severity of Achilles tendinopathy. It also resulted in redistribution of relative electrical activity, but not metabolic activity, within the triceps surae muscle.
    Full-text · Article · May 2014 · Journal of Applied Physiology

Publication Stats

8k Citations
593.88 Total Impact Points

Institutions

  • 1998-2015
    • IT University of Copenhagen
      København, Capital Region, Denmark
  • 1996-2015
    • Bispebjerg Hospital, Copenhagen University
      • Institute for Sports Medicine
      København, Capital Region, Denmark
  • 2013
    • Lund University
      Lund, Skåne, Sweden
  • 2012
    • University of North Carolina at Charlotte
      Charlotte, North Carolina, United States
  • 2007-2012
    • Institute of Sports Medicine Copenhagen
      København, Capital Region, Denmark
  • 2006
    • University of Turku
      • Turku PET Centre
      Turku, Varsinais-Suomi, Finland
  • 1993
    • Lenox Hill Hospital
      New York City, New York, United States