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Considerations on the human Achilles tendon moment arm for in vivo triceps surae muscle-tendon unit force estimates.
Holzer, D, Paternoster, FK, Hahn, D, Siebert, T, Seiberl, W
Scientific reports. 2020;(1):19559
Abstract
Moment arm-angle functions (MA-a-functions) are commonly used to estimate in vivo muscle forces in humans. However, different MA-a-functions might not only influence the magnitude of the estimated muscle forces but also change the shape of the muscle's estimated force-angle relationship (F-a-r). Therefore, we investigated the influence of different literature based Achilles tendon MA-a-functions on the triceps surae muscle-tendon unit F-a-r. The individual in vivo triceps torque-angle relationship was determined in 14 participants performing maximum voluntary fixed-end plantarflexion contractions from 18.3° ± 3.2° plantarflexion to 24.2° ± 5.1° dorsiflexion on a dynamometer. The resulting F-a-r were calculated using 15 literature-based in vivo Achilles tendon MA-a-functions. MA-a-functions affected the F-a-r shape and magnitude of estimated peak active triceps muscle-tendon unit force. Depending on the MA-a-function used, the triceps was solely operating on the ascending limb (n = 2), on the ascending limb and plateau region (n = 12), or on the ascending limb, plateau region and descending limb of the F-a-r (n = 1). According to our findings, the estimated triceps muscle-tendon unit forces and the shape of the F-a-r are highly dependent on the MA-a-function used. As these functions are affected by many variables, we recommend using individual Achilles tendon MA-a-functions, ideally accounting for contraction intensity-related changes in moment arm magnitude.
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2.
Effect of habitual foot-strike pattern on the gastrocnemius medialis muscle-tendon interaction and muscle force production during running.
Swinnen, W, Hoogkamer, W, Delabastita, T, Aeles, J, De Groote, F, Vanwanseele, B
Journal of applied physiology (Bethesda, Md. : 1985). 2019;(3):708-716
Abstract
The interaction between gastrocnemius medialis (GM) muscle and Achilles tendon, i.e., muscle-tendon unit (MTU) interaction, plays an important role in minimizing the metabolic cost of running. Foot-strike pattern (FSP) has been suggested to alter MTU interaction and subsequently the metabolic cost of running. However, metabolic data from experimental studies on FSP are inconsistent, and a comparison of MTU interaction between FSP is still lacking. We, therefore, investigated the effect of habitual rearfoot and mid-/forefoot striking on MTU interaction, ankle joint work, and plantar flexor muscle force production while running at 10 and 14 km/h. GM muscle fascicles of 9 rearfoot and 10 mid-/forefoot strikers were tracked using dynamic ultrasonography during treadmill running. We collected kinetic and kinematic data and used musculoskeletal models to determine joint angles and calculate MTU lengths. In addition, we used dynamic optimization to assess plantar flexor muscle forces. During ground contact, GM fascicle shortening ( P = 0.02) and average contraction velocity ( P = 0.01) were 40-45% greater in rearfoot strikers than mid-/forefoot strikers. Differences in contraction velocity were especially prominent during early ground contact. Moreover, GM ( P = 0.02) muscle force was greater during early ground contact in mid-/forefoot strikers than rearfoot strikers. Interestingly, we did not find differences in stretch or recoil of the series elastic element between FSP. Our results suggest that, for the GM, the reduced muscle energy cost associated with lower fascicle contraction velocity in mid-/forefoot strikers may be counteracted by greater muscle forces during early ground contact. NEW & NOTEWORTHY Kinetic and kinematic differences between foot-strike patterns during running imply (not previously reported) altered muscle-tendon interaction. Here, we studied muscle-tendon interaction using ultrasonography. We found greater fascicle contraction velocities and lower muscle forces in rearfoot compared with mid-/forefoot strikers. Our results suggest that the higher metabolic energy demand due to greater fascicle contraction velocities might offset the lower metabolic energy demand due to lower muscle forces in rearfoot compared with mid-/forefoot strikers.
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3.
Uniaxial repetitive mechanical overloading induces influx of extracellular calcium and cytoskeleton disruption in human tenocytes.
Chen, W, Deng, Y, Zhang, J, Tang, K
Cell and tissue research. 2015;(2):577-587
Abstract
Tendon calcification is common in the Achilles tendon, and injuries affect not only athletes, but also the general population. However, the underlying cellular mechanisms are not yet fully understood. In this study, we isolated healthy human tenocytes and subjected them to uniaxial mechanical stretching (at 1.0 Hz) for various stretch times (4 h, 8 h, 12 h) or magnitudes (0%, 4%, 8%, 12%). The extracellular calcium chelator EGTA, calcium channel inhibitor MnCl2, nifedipine, or various doses of exogenous calcium were administered to these cells with or without mechanical overloading. The intracellular calcium concentration was determined by using a Fluo-3/AM fluorescence probe, and the cytoskeleton was revealed by F-actin Phalloidin staining. The intracellular calcium concentration increased in a magnitude- and time-dependent manner following stretching. These increases were suppressed by EGTA, MnCl2, or nifedipine. Additionally, cytoskeleton F-actin was disrupted significantly by stretching in a time-dependent manner. When extracellular calcium was applied, the intracellular calcium concentration increased, and F-actin was disrupted dramatically under mechanical stretching compared with non-stretched cells. Thus, repetitive mechanical overloading induces the accumulation of abnormally high concentrations of intracellular calcium resulting from extracellular calcium influx mediated, at least in part, by membrane calcium channels and finally causes cytoskeleton disorganization and tenocyte dysfunction. These findings provide novel experimental evidence for the pathology of tendon calcification and indicate that the blockade of calcium influx is a potential target for the prevention and treatment of calcific tendinopathy.
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4.
Weight-Bearing in the Nonoperative Treatment of Acute Achilles Tendon Ruptures: A Randomized Controlled Trial.
Young, SW, Patel, A, Zhu, M, van Dijck, S, McNair, P, Bevan, WP, Tomlinson, M
The Journal of bone and joint surgery. American volume. 2014;(13):1073-1079
Abstract
BACKGROUND The rate of Achilles tendon ruptures is increasing, but there is a lack of consensus on treatment of acute injuries. The purpose of this trial was to compare outcomes of weight-bearing casts with those of traditional casts in the treatment of acute Achilles tendon ruptures. METHODS Eighty-four patients with an acute Achilles tendon rupture were recruited over a two-year period. Patients were randomized to be treated with either a weight-bearing cast with a Böhler iron or a non-weight-bearing cast for eight weeks. Patients underwent muscle dynamometry testing at six months, with additional follow-up at one and two years. The primary outcomes that were assessed were the rerupture rate and the time taken to return to work. Secondary outcomes included return to sports, ankle pain and stiffness, footwear restrictions, and patient satisfaction. RESULTS There were no significant differences between groups with regard to patient demographics or activity levels prior to treatment. At the time of follow-up at two years, one (3%) of the thirty-seven patients in the weight-bearing group and two (5%) of the thirty-seven in the non-weight-bearing group had sustained a rerupture (p = 0.62). The patients in the weight-bearing group experienced less subjective stiffness at one year. There were no significant differences in time taken to return to work, Leppilahti scores, patient satisfaction, pain, or return to sports between the groups. CONCLUSIONS Use of weight-bearing casts for the nonoperative treatment of Achilles tendon ruptures appears to offer outcomes that are at least equivalent to those of non-weight-bearing casts. The overall rerupture rate in this study was low, supporting the continued use of initial nonoperative management for the treatment of acute Achilles tendon ruptures. LEVELS OF EVIDENCE Therapeutic Level I. See Instructions for Authors for a complete description of levels of evidence.
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5.
Evolution of the Achilles tendon: The athlete's Achilles heel?
Malvankar, S, Khan, WS
Foot (Edinburgh, Scotland). 2011;(4):193-7
Abstract
The Achilles tendon is believed to have first developed two million years ago enabling humans to run twice as fast. However if the Achilles tendon is so important in terms of evolution, then why is this tendon so prone to injury - especially for those more active like athletes. The Achilles tendon had an integral role in evolving apes from a herbivorous diet to early humans who started hunting for food over longer distances, resulting in bipedal locomotion. Evolutionary advantages of the Achilles tendon includes it being the strongest tendon in the body, having an energy-saving mechanism for fast locomotion, allows humans to jump and run, and additionally is a spring and shock absorber during gait. Considering these benefits it is therefore not surprising that studies have shown athletes have thicker Achilles tendons than subjects who are less active. However, contradictory to these findings that show the importance of the Achilles tendon for athletes, it is well known that obtaining an Achilles tendon injury for an athlete can be career-altering. A disadvantage of the Achilles tendon is that the aetiology of its pathology is complicated. Achilles tendon ruptures are believed to be caused by overloading the tensed tendon, like during sports. However studies have also shown athlete Achilles tendon ruptures to have degenerative changes in the tendon. Other flaws of the Achilles tendon are its non-uniform vascularity and incomplete repair system which may suggest the Achilles tendon is on the edge of evolution. Research has shown that there is a genetic influence on the predisposition a person has towards Achilles tendon injuries. So if this tendon is here to stay in our anatomy, and it probably is due to the slow rate of evolution in humans, research in genetic modification could be used to decrease athletes' predisposition to Achilles tendinopathy.
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6.
The use of Achilles tendon sonography to distinguish familial hypercholesterolemia from other genetic dyslipidemias.
Junyent, M, Gilabert, R, Zambón, D, Núñez, I, Vela, M, Civeira, F, Pocoví, M, Ros, E
Arteriosclerosis, thrombosis, and vascular biology. 2005;(10):2203-8
Abstract
OBJECTIVE Achilles tendon (AT) xanthomas, specific for familial hypercholesterolemia (FH), may be clinically undetectable. We assessed the usefulness of AT sonography in the diagnosis of FH. METHODS AND RESULTS Sonographic AT characteristics were evaluated in 127 subjects with FH (81 genetically ascertained), 84 familial combined hyperlipidemia, 79 polygenic hypercholesterolemia, and 88 normolipidemic controls. Abnormal echostructure (sonographic xanthoma) was noted only in FH. AT thickness was higher (P<0.001) in FH men and women compared with all of the other groups and, in FH mutation carriers but not in others, correlated positively with low-density lipoprotein cholesterol (r=0.345; P<0.001) and negatively with high-density lipoprotein cholesterol (r=-0.265, P=0.015). Thickness thresholds for the diagnosis of FH with specificity >80%, as were derived from receiver operating curves, were 5.3 and 5.7 mm in men < and >45 years, and 4.8 and 4.9 mm in women < and >50 years, respectively. In FH mutation carriers, sonographic findings increased the clinical diagnosis of xanthomas from 35 (43%) to 55 (68%). Using thresholds in validation sets of 70 genetically identified FH and 54 dyslipidemic non-FH correctly classified 80% and 88%, respectively. CONCLUSIONS Sonographic AT characteristics are normal in non-FH dyslipidemias. Identification of suspected FH by ultrasound using sex- and age-specific AT thickness thresholds is recommended.
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7.
Pathogenesis, detection and treatment of Achilles tendon xanthomas.
Tsouli, SG, Kiortsis, DN, Argyropoulou, MI, Mikhailidis, DP, Elisaf, MS
European journal of clinical investigation. 2005;(4):236-44
Abstract
Tendon xanthomatosis often accompanies familial hypercholesterolaemia, but it can also occur in other pathologic states. Achilles tendons are the most common sites of tendon xanthomas. Low-density lipoprotein (LDL) derived from the circulation accumulates into tendons. The next steps leading to the formation of Achilles tendon xanthomas (ATX) are the transformation of LDL into oxidized LDL (oxLDL) and the active uptake of oxLDL by macrophages within the tendons. Although physical examination may reveal Achilles tendon xanthomas (ATX), there are several imaging methods for their detection. It is worth mentioning that ultrasonography is the method of choice in everyday clinical practice. Although several treatments for Achilles tendon xanthomas (ATX) have been proposed (LDL apheresis, statins, etc.), they target mostly in the treatment of the basic metabolic disorder of lipid metabolism, which is the main cause of these lesions. In this review we describe the formation, detection, differential diagnosis and treatment of ATX as well as the relationship between tendon xanthomas and atheroma.
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8.
Common conditions of the achilles tendon.
Mazzone, MF, McCue, T
American family physician. 2002;(9):1805-10
Abstract
The Achilles tendon, the largest tendon in the body, is vulnerable to injury because of its limited blood supply and the combination of forces to which it is subjected. Aging and increased activity (particularly velocity sports) increase the chance of injury to the Achilles tendon. Although conditions of the Achilles tendon are occurring with increasing frequency because the aging U.S. population is remaining active, the diagnosis is missed in about one fourth of cases. Injury onset can be gradual or sudden, and the course of healing is often lengthy. A thorough history and specific physical examination are essential to make the appropriate diagnosis and facilitate a specific treatment plan. The mainstay of treatment for tendonitis, peritendonitis, tendinosis, and retrocalcaneobursitis is ice, rest, and nonsteroidal anti-inflammatory drugs, but physical therapy, orthoties, and surgery may be necessary in recalcitrant cases. In patients with tendon rupture, casting or surgery is required. Appropriate treatment often leads to full recovery.