Bjarki Haraldsson - Academia.edu (original) (raw)

Papers by Bjarki Haraldsson

International Journal of Environmental Research and Public Health, Mar 9, 2021

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Journal of Applied Physiology, Feb 1, 2012

Tendons are strong hierarchical structures, but how tensile forces are transmitted between differ... more Tendons are strong hierarchical structures, but how tensile forces are transmitted between different levels remains incompletely understood. Collagen fibrils are thought to be primary determinants of whole tendon properties, and therefore we hypothesized that the whole human patellar tendon and its distinct collagen fibrils would display similar mechanical properties. Human patellar tendons (n ϭ 5) were mechanically tested in vivo by ultrasonography. Biopsies were obtained from each tendon, and individual collagen fibrils were dissected and tested mechanically by atomic force microscopy. The Young's modulus was 2.0 Ϯ 0.5 GPa, and the toe region reached 3.3 Ϯ 1.9% strain in whole patellar tendons. Based on dry cross-sectional area, the Young's modulus of isolated collagen fibrils was 2.8 Ϯ 0.3 GPa, and the toe region reached 0.86 Ϯ 0.08% strain. The measured fibril modulus was insufficient to account for the modulus of the tendon in vivo when fibril content in the tendon was accounted for. Thus, our original hypothesis was not supported, although the in vitro fibril modulus corresponded well with reported in vitro tendon values. This correspondence together with the fibril modulus not being greater than that of tendon supports that fibrillar rather than interfibrillar properties govern the subfailure tendon response, making the fibrillar level a meaningful target of intervention. The lower modulus found in vitro suggests a possible adverse effect of removing the tissue from its natural environment. In addition to the primary work comparing the two hierarchical levels, we also verified the existence of viscoelastic behavior in isolated human collagen fibrils. atomic force microscopy; collagen; fibril dimensions; modulus; toe region TENDON TISSUE PLAYS AN ESSENTIAL role in transmitting contractile forces to bone to generate movement and is therefore uniquely designed to resist sizeable loads (up to ϳ8 times body wt) during human locomotion (16, 22). However, despite this inherent quality, both overuse injuries and complete tendon ruptures occur. The precise mechanism(s) for tendon injuries remains unknown, but it is possible that there are one or more "weak links" in the tendon structure (36).

Scandinavian Journal of Medicine & Science in Sports, Oct 1, 2009

Overload tendon injuries are frequent in recreational and elite sports. The optimal treatment str... more Overload tendon injuries are frequent in recreational and elite sports. The optimal treatment strategy remains unknown, but local administration of corticosteroids is one common treatment option. The direct effects of the corticosteroid administration on the tissue are not fully understood. The present study examined the biomechanical effects of intratendinous corticosteroid injections on healthy rat-tail tendon collagen fascicles. A total of 24 Wistar male rats were divided into (A) a corticosteroid group where the animals were injected in the tail tendon with methylprednisolone acetate, 1.0 mL of 40 mg/mL mixed with 1.0 mL 9% saline (n=12), and (B) a control group that was injected with 9% saline (n=12). Three days after the injections, the animals were sacrificed and single individual collagen fascicles were collected and underwent displacement to failure. Corticosteroid administration significantly reduced tensile fascicle yield strength by 16% and Young's modulus by 14% compared with sham treatment (10.5+/-0.8 vs 12.4+/-0.5 MPa, P< or =0.05, and 537+/-27 vs 641+/-30 MPa, P<0.05, respectively), while the strain properties were unaffected. Peak stress was similar between the two groups. There was no difference in fascicle diameter between the two groups.

Disability & Rehabilitation, 2008

Purpose. Tendon structures have been studied for decades, but over the last decade, methodologica... more Purpose. Tendon structures have been studied for decades, but over the last decade, methodological development and renewed interest for metabolic, circulatory and tissue protein turnover in tendon tissue has resulted in a rising amount of investigations. Method. This paper will detail the various modern investigative techniques available to study tendons. Results. There are a variety of investigative methods available to study the correlations between mechanics and biology in tendons. Conclusion. The available methodologies not only allow for potential insight into physiological and pathophysiological mechanisms in tendon tissue, but also, to some extent, allow for more elaborate studies of the intact human tendon.

International Journal of Environmental Research and Public Health

Muscle strength assessment is fundamental to track the progress of performance and prescribe corr... more Muscle strength assessment is fundamental to track the progress of performance and prescribe correct exercise intensity. In field settings, simple tests are preferred. This study develops equations to estimate maximal muscle strength in upper- and lower-extremity muscles based on submaximal elastic resistance tests. Healthy adults (n = 26) performed a maximal test (1 RM) to validate the ability of the subsequent submaximal tests to determine maximal muscle strength, with elastic bands. Using a within-group repeated measures design, three submaximal tests of 40%, 60%, and 80% during (1) shoulder abduction, (2) shoulder external rotation, (3) hip adduction, and (4) prone knee flexion were performed. The association between number of repetitions and relative intensity was modeled with both 1st and 2nd order polynomials to determine the best predictive validity. For both upper-extremity tests, a strong linear association between repetitions and relative intensity was found (R2 = 0.97–1....

Sensors (Basel, Switzerland), 2021

Purpose: We aimed to investigate the influence of wearing a ballistic vest on physical performanc... more Purpose: We aimed to investigate the influence of wearing a ballistic vest on physical performance in police officers. Methods: We performed a cross-over study to investigate the influence of wearing a ballistic vest on reaction and response time, lumbar muscle endurance and police vehicle entry and exit times. Reaction and response time was based on a perturbation setup where the officers’ pelvises were fixed and EMG of lumbar and abdominal muscles was recorded. We used a modified Biering–Sørensen test to assess the lumbar muscle endurance and measured duration of entry and exit maneuvers in a variety of standard-issue police cars. Results: There was a significant difference of 24% in the lumbar muscle endurance test (no vest: 151 s vs. vest: 117 s), and the police officers experienced higher physical fatigue after the test when wearing a vest. Furthermore, officers took longer to both enter and exit police cars when wearing a vest (range: 0.24–0.56 s) depending on the model of the...

Acute exercise induces collagen synthesis in both tendon and muscle. This indicates an adaptive r... more Acute exercise induces collagen synthesis in both tendon and muscle. This indicates an adaptive response in the connective tissue of the muscle-tendon unit. However, it is not known if regulation of collagen expression is dependent on the type of contraction performed by the muscle. Furthermore, the possible involvement of collagen inducing growth factors, such as transforming growth factor-β-1 (TGF-β-1) and connective tissue growth factor (CTGF), in muscle/tendon adaptation has not been investigated. Female Sprague-Dawley rats were subjected to 4 days of concentric-, eccentricor isometric training (n=7-9 per group) of the medial gastrocnemius, by stimulation of the sciatic nerve during general anaesthesia. RNA was extracted from medial gastrocnemiusand Achilles tendon tissue 24 h after the last training bout, and mRNA levels for collagens I and -III, TGF-β-1 and CTGF were measured by Northern blotting and/or Real-time RT PCR. In tendon, expression of TGF-β-1 and collagens I and III...

Scandinavian Journal of Medicine & Science in Sports, 2009

Journal of Applied Physiology, 2010

The human patellar tendon is frequently affected by tendinopathy, but the etiology of the conditi... more The human patellar tendon is frequently affected by tendinopathy, but the etiology of the condition is not established, although differential loading of the anterior and posterior tendon may be associated with the condition. We hypothesized that changes in fibril morphology and collagen cross-linking would parallel differences in material strength between the anterior and posterior tendon. Tendon fascicles were obtained from elective ACL surgery patients and tested micromechanically. Transmission electron microscopy was used to assess fibril morphology, and collagen cross-linking was determined by HPLC and calorimetry. Anterior fascicles were markedly stronger (peak stress: 54.3 ± 21.2 vs. 39.7 ± 21.3 MPa; P < 0.05) and stiffer (624 ± 232 vs. 362 ± 170 MPa; P < 0.01) than posterior fascicles. Notably, mature pyridinium type cross-links were less abundant in anterior fascicles (hydroxylysylpyridinoline: 0.859 ± 0.197 vs. 1.416 ± 0.250 mol/mol, P = 0.001; lysylpyridinoline: 0.02...

Journal of Applied Physiology, 2004

The present study investigated the mechanical properties of tendon fascicles from the anterior an... more The present study investigated the mechanical properties of tendon fascicles from the anterior and posterior human patellar tendon. Collagen fascicles from the anterior and posterior human patellar tendon in healthy young men (mean ± SD, 29.0 ± 4.6 yr, n = 6) were tested in a mechanical rig. A stereoscopic microscope equipped with a digital camera recorded elongation. The fascicles were preconditioned five cycles before the failure test based on pilot data on rat tendon fascicle. Human fascicle length increased with repeated cycles ( P < 0.05); cycle 5 differed from cycle 1 ( P < 0.05), but not cycles 2–4. Peak stress and yield stress were greater for anterior (76.0 ± 9.5 and 56.6 ± 10.4 MPa, respectively) than posterior fascicles (38.5 ± 3.9 and 31.6 ± 2.9 MPa, respectively), P < 0.05, while yield strain was similar (anterior 6.8 ± 1.0%, posterior 8.7 ± 1.4%). Tangent modulus was greater for the anterior (1,231 ± 188 MPa) than the posterior (583 ± 122 MPa) fascicles, P &lt...

International Journal of Experimental Pathology, 2007

It is well established that women are more likely to sustain certain connective tissue injuries t... more It is well established that women are more likely to sustain certain connective tissue injuries than men during physical activities (Jones et al. 1993; Bijur et al. 1997). For example, the incidence of anterior cruciate ligament injuries in women is reported to be up to six times that in men participating in similar physical activities (Bjordal et al. 1997; Hewett et al. 2001). The annual cost for these injuries is large (Griffin et al. 2000), and yet the underlying reasons for this genderspecific difference in connective tissue injury remains an enigma. Oestrogen receptor activity is modulated by estradi-ol (Ciana et al. 2003), and in vitro studies show that estradiol has an inhibiting effect upon collagen formation in ligaments(Liu et al. 1997; Yu et al. 2001), which gives us reason to believe that tendon tissue adaptation to mechanical loading may differ between men and women. We investigated whether a gender difference existed with regards to resting and exercise-induced collagen protein synthesis, tissue mechanical properties and morphology of human tendon, and to what extent this is influenced by circulating levels of estradiol.

Connective Tissue Research, 2009

Conclusive insight into the microscopic principles that govern the strength of tendon and related... more Conclusive insight into the microscopic principles that govern the strength of tendon and related connective tissues is lacking and the importance of collagen cross-linking has not been firmly established. The combined application of whole-tissue mechanical testing and atomic force spectroscopy allowed for a detailed characterization of the effect of cross-linking in rat-tail tendon. The cross-link inducing agent glutaraldehyde augmented the tensile strength of tendon fascicles. Stress at failure increased from approximately 8 MPa to approximately 39 MPa. The mechanical effects of glutaraldehyde at the tendon fibril level were examined by atomic force microscopy. Peak forces increased from approximately 1379 to approximately 2622 pN while an extended Hertz fit of force-indentation data showed a approximately 24 fold increase in Young&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s modulus on indentation. The effect of glutaraldehyde cross-linking on the tensile properties of a single collagen fibril was investigated by a novel methodology based on atomic force spectroscopy. The Young&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s modulus of a secluded fibril increased from approximately 407 MPa to approximately 1.1 GPa with glutaraldehyde treatment. Collectively, the findings indicate that cross-linking at the level of the collagen fibril is of key importance for the mechanical strength of tendon tissue. However, when comparing the effects at the level of the tendon fascicle and fibril, respectively, further questions are prompted regarding the pathways of force through the tendon microstructure as fibril strength seems to surpass that of the tendon fascicle.

Clinical Biomechanics, 2006

Mechanical properties of the human patellar tendon are largely based on cadaver studies, which ma... more Mechanical properties of the human patellar tendon are largely based on cadaver studies, which may not necessarily be applicable to the human patellar tendon, in vivo. While ultrasonography is an attractive non-invasive method for studying human, in vivo, muscle-tendon behaviour, it has mostly been used to examine Achilles tendon properties. We examine the accuracy of human patellar tendon elongation, in vivo, and its within-day and between-day reproducibility. Subjects performed four maximal 10-s ramp isometric knee extension trials to examine within-day reproducibility, and the procedure was repeated on a separate day to assess between-day reproducibility. Continuous and simultaneous ultrasonography based measurement of both tibial and patellar movement together with patellar tendon force yielded mechanical estimates. Longitudinal tibial displacement corresponded to 45 (SEM 8) % of the overall tibia-patella displacement. For within-day reproducibility there was no difference between trials for stiffness [trial a, 4334 (SEM 562) N/mm; trial b, 4273 (SEM 533) N/mm], strain [trial a, 6.9 (SEM 0.6) %; trial b, 6.8 (SEM 0.7) %] or elastic modulus [trial a, 1.09 (SEM 0.12) GPa; trial b, 1.09 (SEM 0.10) GPa]. The within day correlation coefficient and typical error were 0.95 and 9.9% for stiffness, 0.97 and 5.5% for strain, and 0.94 and 9.4% for elastic modulus. The corresponding values for between days were 0.94 and 8.7% for stiffness, 0.98 and 3.7% for strain, and 0.86 and 9.6% for elastic modulus. The present methodology of assessing human patellar tendon elongation, strain and stiffness, in vivo, is accurate and reproducible which permits its use in future investigations of patellar tendon biomechanics and the potential effects of various interventions.

The American Journal of Sports Medicine, 2006

Background Overuse tendon injuries are frequent. Corticosteroid injections are commonly used as t... more Background Overuse tendon injuries are frequent. Corticosteroid injections are commonly used as treatment, although their direct effects on the material properties of the tendon are poorly understood. Purpose To examine the influence of corticosteroids on the tensile strength of isolated collagen fascicles. Study Design Controlled laboratory study. Methods Single strands (300-500 [.mu]m) of rat-tail collagen fascicles were incubated in either high (1 mL of 40 mgmL-1 mixed with 0.5 mL saline 9%) or low (1 mL of 40 mgmL-1 mixed with 2 mL saline 9%) concentration of methylprednisolone acetate (Depomedrol) for 3 or 7 days, while the control segment from the same fascicle was kept in saline (N = 64). After the incubation period, the fascicles underwent displacement to failure in a mechanical test rig at 0.13 mm/s, and thereafter hydroxylysyl pyridinoline and lysyl pyridinoline cross-link content was evaluated in a high-performance liquid chromatography system. Data for each group were an...