Objectives. Histological examination of pathological tendon generally does not reveal signs of inflammation. However, the inflammatory cytokine IL-6 has been shown to be expressed in ruptured rotator cuff tendon. The aim of this study was to investigate the expression of IL-6 family members in painful posterior tibialis tendon (PTT) and in painful and ruptured Achilles tendon (AT) compared with normal tendon.Methods. AT samples were obtained from cadavers (normal) or from patients undergoing surgical procedures to treat chronic painful tendinopathy or ruptured tendon. PTT samples were obtained from patients undergoing surgery for other reasons (normal) and from patients with PTT dysfunction (painful). Total RNA was extracted and mRNA expression was analysed by quantitative real-time PCR.Results. Collagen type I α-chain I (COL1A1) expression was increased in both painful PTT and AT compared with normal. Ciliary neurotrophic factor levels were increased in painful PTT only. In the painful AT, cyclooxygenase-2 (COX2) and IL-6 expression increased compared with normal. In the ruptured AT, levels of VEGF A, COX2, oncostatin-M, leukaemia inhibitory factor and IL-6 expression were higher compared with both normal and painful AT. IL-6R expression decreased in both painful and ruptured AT compared with normal.Conclusion. Painful AT and PTT show different expression patterns, indicating a substantial difference between those two tendinopathies. Inflammatory markers are up-regulated in painful and particularly in ruptured AT, pointing towards a role of inflammation not only in rupture healing, but also in Achilles tendinopathy.

Repetitive strain or ‘overuse’ is thought to be a major factor contributing to the development of tendinopathy. The aims of our study were to develop a novel cyclic loading system, and use it to investigate the effect of defined loading conditions on the mechanical properties and gene expression of isolated tendon fascicles. Tendon fascicles were dissected from bovine-foot extensors and subjected to cyclic tensile strain (1 Hz) at 30% or 60% of the strain at failure, for 0 h (control), 15 min, 30 min, 1 h, or 5 h. Post loading, a quasi-static test to failure assessed damage. Gene expression at a selected loading regime (1 h at 30% failure strain) was analyzed 6 h post loading by quantitative real-time polymerase chain reaction. Compared with unloaded controls, loading at 30% failure strain took 5 h to lead to a significant decrease in failure stress, whereas loading to 60% led to a significant reduction after 15 min. Loading for 1 h at 30% failure strain did not create significant structural damage, but increased Collagen-1-alpha-chain-1 and interleukin-6 (IL6) expression, suggesting a role of IL6 in tendon adaptation to exercise. Correlating failure properties with fatigue damage provides a method by which changes in gene expression can be associated with different degrees of fatigue damage.

The aim of this study was to evaluate the suitability of ultrasonography for the quantification of gastrocnemius muscle architecture in healthy young children. The variation and reliability of measurement of muscle thickness, pennation angle and fibre length of the medial gastrocnemius were determined, using stationary and portable ultrasound machines, in 13 boys and eight girls aged 4-10. Ultrasound images were obtained from each leg, in duplicate, with the ankle at 90 degrees , then at maximal plantar flexion, with the two machines within the same session. The same set of 16 scans was repeated in four children 4-6 weeks later. The mean muscle thickness, pennation angle and fibre length differed between ankle positions and between legs. Measurements obtained using the two machines established similar values with no significant differences in absolute values and coefficients of variation (CV). For duplicate images taken during the same session for the same leg, ankle position and machine, the CV and intraclass correlation coefficients (ICC) ranged, respectively, from 2.1% to 3.1% and 0.94-0.98 for muscle thickness, from 4.1% to 6.0% and 0.85-0.96 for pennation angle and from 4.5% to 6.3% and 0.87-0.96 for fibre length. Corresponding values for variables for the same child measured on two separate occasions were within the same ranges, all being similar to reliability data reported previously for adult muscle. Muscle thickness, pennation angle and fibre length of the medial gastrocnemius can therefore be quantified reliably, using either a stationary or portable ultrasound machine, in healthy young children.

The aims of this study were to characterize the pattern of voluntary activity of young rats in response to resistance loading on running wheels and to determine the effects of the activity on the growth of six limb skeletal muscles. Male Sprague-Dawley rats (4 weeks old) were housed individually with a resistance running wheel (R-RUN, n = 7) or a conventional free-spinning running wheel (F-RUN, n = 6) or without a wheel, as non-running control animals (CON, n = 6). The torque required to move the wheel in the R-RUN group was progressively increased, and the activity (velocity, distance and duration of each bout) of the two running wheel groups was recorded continuously for 45 days. The R-RUN group performed many more, shorter and faster bouts of running than the F-RUN group, yet the mean daily distance was not different between the F-RUN (1.3 ± 0.2 km) and R-RUN group (1.4 ± 0.6 km). Only the R-RUN resulted in a significantly (P < 0.05) enhanced muscle wet mass, relative to the increase in body mass, of the plantaris (23%) and vastus lateralis muscle (17%), and the plantaris muscle fibre crosssectional area, compared with CON. Both F-RUN and R-RUN led to a significantly greater wet mass relative to increase in body mass and muscle fibre cross-sectional area in the soleus muscle compared with CON. We conclude that the pattern of voluntary activity on a resistance running wheel differs from that on a free-spinning running wheel and provides a suitable model to induce physiological muscle hypertrophy in rats.

Stress, strain and modulus are regularly used to characterize material properties of tissue samples. However, when comparing results from different studies it is evident the reported material properties, particularly failure strains, vary hugely. The aim of our study was to characterize how and why specimen length and cross-sectional area (CSA) appear to influence failure stress, strain and modulus in fascicles from two functionally different tendons. Fascicles were dissected from five rat tails and five bovine foot extensors, their diameters determined by a laser micrometer, and loaded to failure at a range of grip-to-grip lengths. Strain to failure significantly decreased with increasing in specimen length in both rat and bovine fascicles, while modulus increased. Specimen length did not influence failure stress in rat tail fascicles, although in bovine fascicles it was significantly lower in the longer 40 mm specimens compared to 5 and 10 mm specimens. The variations in failure strain and modulus with sample length could be predominantly explained by end-effects. However, it was also evident that strain fields along the sample length were highly variable and notably larger towards the ends of the sample than the mid-section even at distances in excess of 5 mm from the gripping points. Failure strain, stress and modulus correlated significantly with CSA at certain specimen lengths. Our findings have implications for the mechanical testing of tendon tissue: while it is not always possible to control for fascicle length and/or CSA, these parameters have to be taken into account when comparing samples of different dimensions.

Although the training induced adaptations of the investigated tissues follows similar principles in children as in adults, the magnitude of the adaptive response appears to be more subtle. As studies investigating physiological adaptation in youth athletes are sparse, more research in this area is warranted to elucidate the specific physiological stimulus-response relationship necessary for effective training programs and injury prevention.

Compared with muscle or bone, there is a lack of information about the relationship between tendon adaptation and the applied loading characteristic. The purpose of the present study was to analyze the effect of different exercise modes characterized by very distinct loading patterns on the mechanical, morphological, and biochemical properties of the Achilles tendon. Sixty-four female Sprague-Dawley rats were divided into five groups: nonactive age-matched control (AMC; n = 20), voluntary wheel running (RT; n = 20), vibration strength-trained (LVST; n = 12), high-vibration strength-trained (HVST; n = 6), and high strength-trained (HST; n = 6) group. After a 12-wk-long experimental period, the Achilles tendon was tested mechanically and the cross-sectional area, the soleus and gastrocnemius muscle mass, and mRNA concentration of collagen I, collagen III, tissue inhibitor of metalloproteinase-1 (TIMP-1), transforming growth factor-beta, connective tissue growth factor, and matrix metalloproteinase-2 was determined. Neither in the LVST nor in the HVST group could any adaptation of the Achilles tendon be detected, although the training had an effect on the gastrocnemius muscle mass in the LVST group (P < 0.05). In the HST group, the highest creep was found, but the effect was more pronounced compared with the LVST group (P < 0.05) than with the AMC group. That indicates that this was rather induced by the low muscle mass rather than by training. However, the RT group had a higher TIMP-1 mRNA concentration in the Achilles tendon in contrast to AMC group (P < 0.05), which suggests that this exercise mode may have an influence on tendon adaptation.

Cyclic and static loading regimes are commonly used to study tenocyte metabolism in vitro and to improve our understanding of exercise-associated tendon pathologies. The aims of our study were to investigate if cyclic and static stress relaxation affected the mechanical properties of tendon fascicles differently, if this effect was reversible after a recovery period, and if the removal of glycosaminoglycans (GAGs) affected sample recovery. Tendon fascicles were dissected frombovine-foot extensors and subjected to 14% cyclic (1 Hz) or static tensile strain for 30 min. Additional fascicles were incubated overnight in buffer with 0.5 U chondroitinase ABC or in buffer alone prior to the static stress-relaxation regime. To assess the effect of different stress-relaxation regimes, a quasi-static test to failure was carried out, either directly post loading or after a 2 h recovery period, and compared with unloaded control fascicles. Both stress-relaxation regimes led to a significant reduction in fascicle failure stress and strain, but this was more pronounced in the cyclically loaded specimens. Removal of GAGs led to more stress relaxation and greater reductions in failure stress after static loading compared to controls. The reduction in mechanical properties was partially reversible in all samples, given a recovery period of 2 h. This has implications for mechanical testing protocols, as a time delay between fatiguing specimens and characterization of mechanical properties will affect the results. GAGs appear to protect tendon fascicles from fatigue effects, possibly by enabling sample hydration.