Tendon Elongation Research Articles

Treatment outcome at 1 year did not differ between use of cast or walker in the first 3 weeks after an acute Achilles tendon rupture. A registry study of 1304 patients from the Danish Achilles tendon database

BackgroundThe best choice of orthosis in the treatment of acute Achilles tendon rupture is still under debate. ObjectiveTo investigate if choice of orthosis in the first 3 weeks of treatment affected patient reported outcome (Achilles tendon Total Rupture Score (ATRS)), tendon elongation (Achilles Tendon Resting Angle (ATRA) and Heel Rise Height (HRH)) and re-rupture. MethodsRegistry study in the Danish Achilles tendon Database. Patients treated with cast and patients treated with walker in the first 3 weeks of treatment were compared using a linear mixed-effects model adjusted for potential confounders. Results1304 patients were included in the study. No clinically relevant difference was found: Adjusted mean difference (using walker the whole period as reference)(95% CI) ATRS after 1 year = 0.1(−3.0; 4.1), ATRS after 6 months = 2.0(−4.5; 5.8), ATRS after 2 years = 3.0(−0.7; 7.0), HRH difference = 0.6(−6.6; 8.2), ATRA difference = 0.03°(−1.5; 1.6), re-rupture(odds ratio) = 0.812(0.4; 1.61). ConclusionPatients treated with cast the first 3 weeks after acute Achilles tendon rupture did not have better treatment outcome than patients treated with walker.

Achilles tendon resting angle is able to detect deficits after an Achilles tendon rupture, but it is not a surrogate for direct measurements of tendon elongation, function or symptoms

PurposeThe aim of this study was to investigate how the Achilles tendon resting angle (ATRA), an indirect measurement of tendon elongation, correlates with ultrasonography (US) measurements of the Achilles tendon length 6 and 12 months after an acute ATR and relates to other clinical outcome measurements such as heel-rise height, jumping ability and patient-reported outcome measurements (PROMs).MethodsPatients were included following acute Achilles tendon rupture (ATR). Achilles tendon length, ATRA, heel-rise height (HRH), drop countermovement jump (Drop CMJ) and PROMs (Achilles tendon total rupture score (ATRS) and physical activity scale (PAS)) were evaluated 6 and 12 months after injury. Achilles tendon length was evaluated using US, while the ATRA was measured with a goniometer.ResultsSixty patients (13 women, 47 men), mean (SD) age 43 (9) years, with an acute ATR undergoing either surgical (35%) or non-surgical (65%) treatment were evaluated. A negative correlation (r = − 0.356, p = 0.010) between relative ATRA and tendon elongation was seen at 12 months after ATR. There were also significant positive correlations at 6 and 12 months between relative ATRA and HRH (r = 0.330, p = 0.011 and r = 0.379, p = 0.004). There were no correlations between ATRA and ATRS or ATRA and Drop CMJ, at either 6 or 12 months after the injury.ConclusionIn combination with other clinical evaluations such as HRH and US, ATRA could be a clinical tool for indirect measurements of tendon elongation. However, ATRA cannot be recommended as a direct surrogate for US for determining Achilles tendon length.Level of evidenceIII.

The Effect of an Additional Core Suture During Pulvertaft Tendon Repair: A Fresh-Frozen Cadaver Study

Pulvertaft tendon repair is a strong suture technique; however, proper tendon tension is impaired by repair site elongation. Therefore, methods to reduce postoperative elongation are warranted. This study aimed to determine the effects of additional core sutures during Pulvertaft tendon repair on repair site elongation and rupture strength. A total of 48 finger extensor tendons were harvested from fresh-frozen cadavers, and tendons with similar diameters were paired. The 24 pairs of tendons were divided into the following 4 groups: group I, 3 interlaced weaves only; group II, 3 interlaced weaves and 2 core suture strands with 4-0 nylon; group III, 3 interlaced weaves and 2 core suture strands with 4-0 FiberWire; and group IV, 4 interlaced weaves only. Each sutured tendon was placed in a Universal Testing Machine, and repair site elongation after repeated traction loads and rupture strength were measured. The mean elongation values were 2.74 ± 0.84 mm, 1.80 ± 0.16 mm, 1.60 ± 0.18 mm, and 1.92 ± 0.18 mm for groups I, II, III, and IV, respectively. The elongation values were significantly lower in groups II, III, and IV than in group I. The mean rupture strengths were 64.9 ± 16.0 N, 94.8 ± 17.2 N, 110.9 ± 21.3 N, and 104.9 ± 17.5 N for groups I, II, III, and IV, respectively. Rupture strengths were significantly higher for groups III and IV than for group I. After adding core sutures during Pulvertaft tendon repair, the elongation amount decreased, and the rupture strength improved. The study showed the effect of additional core sutures during Pulvertaft tendon repair, suggesting that it could be useful in reducing postoperative tendon elongation when extensor tendon transfers are performed.

Complications of Ponseti Technique in Treatment of Idiopathic Club Foot

Background: Clubfoot, or talipes equinovarus, is a congenital deformity that consist of; supination and adduction of the forefoot and midfoot; equinus of hindfoot and varus. It was found that more than 100,000 babies are born each year with congenital clubfoot Objectives: The purpose of this study was to investigate the complications of ponseti method for treatment of children with idiopathic club foot. Subjects and Methods: 50 children with 74 clubfeet were managed by Ponseti method from May 2019 to July 2020 in Al-Wasity teaching hospital with primary correction of the deformity followed sometimes by elongation of Achilles tendon then the patients were followed up till June 2021 and the complications were calculated. Results: complications were 10.8% incomplete correction (mostly equinus) and it was corrected by surgery, 6.7% ulcer on the medial surface of head of 1st metatarsal , 9.4% cast falling and 18.9% relapse. Conclusions: Ponseti technique is a safe and effective method for correction of clubfoot and decreases the need for corrective surgery with minimal complications that can be easily managed.

Electrospun aligned poly(ε-caprolactone) nanofiber yarns guiding 3D organization of tendon stem/progenitor cells in tenogenic differentiation and tendon repair.

Hierarchical anisotropy structure directing 3D cellular orientation plays a crucial role in designing tendon tissue engineering scaffolds. Despite recent development of fabrication technologies for controlling cellular organization and design of scaffolds that mimic the anisotropic structure of native tendon tissue, improvement of tenogenic differentiation remains challenging. Herein, we present 3D aligned poly (ε-caprolactone) nanofiber yarns (NFYs) of varying diameter, fabricated using a dry-wet electrospinning approach, that integrate with nano- and micro-scale structure to mimic the hierarchical structure of collagen fascicles and fibers in native tendon tissue. These aligned NFYs exhibited good in vitro biocompatibility, and their ability to induce 3D cellular alignment and elongation of tendon stem/progenitor cells was demonstrated. Significantly, the aligned NFYs with a diameter of 50 μm were able to promote the tenogenic differentiation of tendon stem/progenitor cells due to the integration of aligned nanofibrous structure and suitable yarn diameter. Rat tendon repair results further showed that bundled NFYs encouraged tendon repair in vivo by inducing neo-collagen organization and orientation. These data suggest that electrospun bundled NFYs formed by aligned nanofibers can mimic the aligned hierarchical structure of native tendon tissue, highlighting their potential as a biomimetic multi-scale scaffold for tendon tissue regeneration.

Persistent Deficits after an Achilles Tendon Rupture: A Narrative Review.

Persistent muscle weakness, tendon elongation, and incomplete return to preinjury level are frequent sequelae after acute Achilles tendon rupture, and evidence-based knowledge of how to best rehabilitate the injury is largely absent in the literature. The objective of this review is to illuminate and discuss to what extent an Achilles tendon rupture affects muscle, tendon, and function when assessed with the Achilles tendon total rupture score (ATRS), muscle strength, muscle cross-sectional area, tendon length, and the heel-rise test. The patient-reported outcome measures (PROM) data in the literature suggest that the recovery takes longer than 6 months (ATRS, 70 out of 100), that one-year postinjury, the ATRS only reaches 82, and that this does not appear to noticeably improve thereafter. Loss of muscle mass, strength, and function can in some cases be permanent. Over the first 6 months postinjury, the tendon undergoes elongation, which appears to be negatively correlated to heel-rise function. More recently, there has been some interest in how muscle length and excursion is related to the reduced function. The available literature indicates that further research is highly warranted and that efforts to restore normal tendon length may improve the likelihood of returning to preinjury level after an Achilles tendon rupture.

Minimally Invasive Mid-Substance Achilles Tendon Repair Using the Percutaneous Achilles Repair System (PARS).

Minimally Invasive Mid-Substance Achilles Tendon Repair Using the Percutaneous Achilles Repair System (PARS).

Elongation of the inferior rectus tendon with fascia lata graft for large vertical squint angles in patients with Graves’ orbitopathy

PurposeTo investigate the use of fascia lata (FL) grafts for inferior rectus muscle (IRM) tendon elongation in patients with large vertical squint angles with Graves’ orbitopathy (GO).MethodsIn this retrospective study, we included a consecutive series of 20 eyes of 13 patients with GO who underwent IRM tendon elongation with FL. Orthoptic and ophthalmologic examinations including measurement of the head posture, the extent of deviation in primary position (PP), elevation, motility, and binocular diplopia at the tangent of Harms were conducted preoperatively and after a mean postoperative time of 10.8 (5.0–35.0) months in all patients.ResultsThe mean total repositioning distance was 9.3 ± 3.6 (3.5–16.0) mm. Postoperatively, we found a significant increase in elevation (5.4 ± 2.4 vs. 2.7 ± 2.4 mm preoperatively, p = 0.011). A significant reduction in vertical squint angle (2.8 ± 3.7 vs. 20.2 ± 18.8 Δ preoperatively, p = 0.004), chin elevation (2.3 ± 3.7 vs. 12.9 ± 6.3° preoperatively, p < 0.001), extorsion in PP (0.1 ± 3.8 vs. 8.4 ± 7.8° preoperatively, p = 0.002), and in elevation (1.8 ± 4.8 vs. 11.1 ± 10.9° preoperatively, p = 0.004) occurred postoperatively. A mean dose–effect relation of 2.6 ± 2.9 Δ/mm was calculated. Postoperatively, the lower eyelid retraction was significantly increased (1.5 ± 1.4 vs. 0.4 ± 0.5 mm preoperatively, p = 0.005).ConclusionIRM tendon elongation with FL is a feasible and effective procedure without relevant risk for surgery-related complications.

Operative versus conservative treatment of acute Achilles tendon ruptures: preliminary results of clinical outcome, kinematic MRI and contrast-enhanced ultrasound

IntroductionThere is no uniform consensus on the gold standard therapy for acute Achilles tendon rupture. The aim of this pilot study was to compare operative and conservative treatment regarding imaging findings and clinical outcome.Materials and methodsSurgically or conservatively treated patients with acute Achilles tendon rupture were retrospectively evaluated. Differences in tendon length and diameter with and without load were analysed using kinematic MRI, tendon perfusion, structural alterations, movement and scar tissue by means of grey-scale and contrast-enhanced ultrasound (CEUS). Intra- and interobserver agreement were recorded.ResultsNo significant difference was detected regarding clinical outcome, B mode ultrasonography, contrast-enhanced sonography or MRI findings, although alterations in MRI-based measurements of tendon elasticity were found for both groups. Considerable elongation and thickening of the injured tendon were detected in both groups.ConclusionBoth, conservative and surgical treatment showed comparable outcomes in our preliminary results and may suggest non-inferiority of a conservative approach.

V-Y plasty combined with gastrocnemius aponeurosis turndown repairing the Myerson type Ⅲ chronic Achilles tendon rupture

To investigate the clinical application and effectiveness of V-Y plasty combined with gastrocnemius aponeurosis turndown in the repair of Myerson type Ⅲ chronic Achilles tendon rupture combined with large tendon defect. Between February 2008 and July 2019, 25 patients underwent the V-Y plasty combined with gastrocnemius aponeurosis turndown to treat the Myerson type Ⅲ chronic Achilles tendon rupture. There were 21 males and 4 females. The age ranged from 17 to 56 years, with an average of 34.3 years. Achilles tendon rupture was caused by sports injury in all patients, and the duration from Achilles tendon rupture to operation was 31-70 days, with an average of 53.9 days. After resection of fibrous scar tissue, the distance of Achilles tendon defect was 7-12 cm, with an average of 9.04 cm. The clinical results were evaluated by the Achilles tendon total rupture score (ATRS), American Orthopaedic Foot and Ankle Society (AOFAS) score, dorsiflexion and heel raise height before and after operation. The donor and recipient wounds of all 25 cases healed by first intention after operation. All patients were followed up 24 months. During the follow-up, 3 patients developed mild wound infection, which was cured after anti-infection treatment. One patient had Achilles tendon exposure, which was cured after local flap transfer and repair. Ultrasound and MRI reexamination at 3-12 months after operation showed no Achilles tendon elongation, adhesion, or re-rupture. At 24 months after operation, the ATRS score, AOFAS score, dorsiflexion and heel raise height of affected side significantly improved when compared with those before operation (P<0.05). However, the dorsiflexion and heel raise height of affected side were still significantly worse than those of the healthy side (P<0.05). V-Y plasty combined with gastrocnemius aponeurosis turndown to repair the chronic Achilles tendon rupture can achieve good effectiveness, and the Achilles tendon function significantly improved after repair. However, the procedure is more invasive and has a long duration of intraoperative wound exposure, causing an increased risk of infection, and the aesthetic is not good.

Reliability and Accuracy of a Time-Efficient Method for the Assessment of Achilles Tendon Mechanical Properties by Ultrasonography.

The assessment of the force–length relationship under mechanical loading is widely used to evaluate the mechanical properties of tendons and to gain information about their adaptation, function, and injury. This study aimed to provide a time-efficient ultrasound method for assessing Achilles tendon mechanical properties. On two days, eleven healthy young non-active adults performed eight maximal voluntary isometric ankle plantarflexion contractions on a dynamometer with simultaneous ultrasonographic recording. Maximal tendon elongation was assessed by digitizing ultrasound images at rest and at maximal tendon force. Achilles tendon stiffness index was calculated from the ratio of tendon force-to-strain. No within- and between-day differences were detected between the proposed method and manual frame by frame tracking in Achilles tendon maximal force, maximal elongation, maximal strain, and stiffness index. The overall coefficient of variation between trials ranged from 3.4% to 10.3% and average difference in tendon tracking between methods was less than 0.6% strain. Furthermore, an additional assessment demonstrated significant differences between elite athletes, healthy young, and older adults in Achilles tendon force and stiffness index. Hence, the analysis has the potential to reliably and accurately monitor changes in Achilles tendon mechanical properties due to aging and altered mechanical loading in a time-efficient manner.

1.7cm elongated Achilles tendon did not alter walking gait kinematics 4.5years after non-surgical treatment.

The aim of the present study was to evaluate Achilles tendon length after non-surgical treatment of acute Achilles tendon rupture (aATR), and to evaluate indirect effects of possible persistent elongation on kinematics. The study was performed as a cross-sectional study based on a population of patients from an RCT regarding non-operative treatment of aATR. Thirty-seven patients out of the 56 in the original RCT participated with at a follow up of 4-5years after aATR. Primary outcome was Achilles tendon elongation. Additional outcomes were Achilles tendon resting angle (ATRA), calf circumference, passive ankle plantar and dorsiflexion and loading pattern. Foot pressure mapping was performed to measure plantar loading distribution pattern; medial and lateral forefoot peak pressure, heel peak pressure, medial versus lateral loading pattern and timing of heel lift during roll over process. The healthy leg was used as a control. The injured Achilles tendon was significantly elongated by 1.7 (SD 1.6) cm compared to the non-injured leg. A slight delay of 2.6% (SD 6.0) was measured in heel lift in the injured side compared to the non-injured leg. We found no significant difference in forefoot peak pressure, medial and lateral peak pressure as well as heel peak pressure, and no correlation was found between Achilles tendon length and pressure measurements. Finally, dorsiflexion was 1.9°(SD1.28) larger, ATRA 8.1°(SD6.7) larger, and calf circumference 1.6cm (SD1.1) lower on the injured leg. The Achilles tendon was 1.7cm elongated 4.5years after the initial injury and significant changes in ATRA, calf circumference and passive dorsiflexion was present. Except for a slight delay in heel lift-off, kinematics during walking was symmetrical between injured and healthy leg, even with an elongated tendon on the injured leg. The clinical relevance of the Achilles tendon elongation is uncertain. II. NCT02760784.

The modified mini-open technique for repairing total ruptured Achilles tendon using fiber wire with calcaneal fixation. A prospective case series

BackgroundThe purpose of this study was to evaluate clinical outcomes and complications of our modified Maffuli's mini-open technique for repairing acute Achilles tendon rupture using fiber wire and calcaneal fixation. Material and methodsBetween January 2017 and August 2020, 21 patients with acute rupture of the Achilles tendon who underwent the modified mini-open Maffulli's procedure have been enrolled in the study. ResultAll surgical incisions healed well without scar adhesions or infections. One year postoperatively, the ATRS score and AOFAS score were 91.2 ± 1.8; 97.2 ± 1.6 respectively; the range of ankle joint movement was normal. Patients could return to their work and their light sporting activities at the time of 16.9 ± 1.1 weeks and 19.7 ± 0.9 weeks postoperatively, respectively. 21 out of 21 patients were able to perform single heel raise. There were no sural nerve injuries, re-ruptures, tendon elongation, or deep vein thromboses. ConclusionWe have shown that the modified Maffulli's technique using fiber wire with a calcaneal fixation for repairing acute Achilles tendon ruptures to be a safe and reliable method without requiring specialized or expensive materials. It allows a durable repairing, a limitation of healing problems, and a quick return to physical therapy and full activity. This technique can be widely employed in a low-income country.

Patients with chronic Achilles tendon rupture have persistent limitations in patient-reported function and calf muscle function one year after surgical treatment \u2013 a case series

PurposeEvaluate the one-year postoperative outcomes in patients with Chronic Achilles tendon rupture.MethodsPatients surgically treated for Chronic Achilles tendon rupture (n = 22, 14 males and 8 females, mean age 61 ± 15) were evaluated by Achilles tendon Total Rupture Score, The Physical Activity Scale, The Foot and Ankle Outcome Score, Calf muscle endurance test, counter movement jump, Hopping, ultrasound measurement of tendon length, Achilles Tendon Resting Angle, dorsi flexion range of motion and calf muscle circumference. Muscle function and tendon length outcomes on the injured side were compared with the healthy side.ResultsThe patients scored a mean of 62 ± 26 on the Achilles tendon Total Rupture Score. Median scores on the injured compared with the healthy side were lower in heel-rise repetitions (20 vs 24 cm, p = 0.004), hel-rise height (8 vs 10 cm, p < 0.001), heel-rise total work (872 vs 1590 joule, p < 0.001) and hopping ratio (0.37 vs 0.48, p = 0.005). Median calf circumference was smaller (37 vs 38 cm, p = 0.001) and the mean tendon elongation greater on the injured side; Achilles tendon resting angle (55 vs 50°, p < 0.001) and ultrasound (22.4 vs 20.5 cm, p = 0.006).ConclusionsAt one year postoperatively, patients with chronic Achilles tendon rupture reported persistent limitations in subjective foot and ankle function. Heel-rise height and total work as well as hopping ratio were not recovered, and there was an elongation of the injured Achilles tendon compared with the healthy tendon.Level of evidence IV

The Copenhagen Achilles Length Measurement Performed at Time of Acute Achilles Tendon Rupture is Correlated to Tendon Elongation After 1 Year

Elongation of the tendon has been proposed as the most important factor leading to poor outcome after acute Achilles tendon rupture (ATR). The aim of this paper was to investigate if Amlang's ultrasound classification (AmC) or the Copenhagen Achilles Length Measurement (CALM) when assessed in the acute phase after ATR could predict elongation 1 y after rupture. 107 males and 27 females, aged 18 to 70 y and treated nonsurgically were included. AmC and CALM were assessed at time of rupture and correlated to elongation measured with CALM and Achilles Tendon Resting Angle (ATRA) at 1 y. Receiver operating characteristic (ROC) analysis was performed to determine a cut off for acceptable elongation at time of rupture given that elongation at 1 y was not to exceed 10%. AmC showed no statistically significant correlation. CALM at baseline correlated to CALM at 1 y r = 0.214 (p = .02) and ATRA at 1 y r = 0.218 (p = .02). The ROC model had AUC = 0.67 for 7% elongation at baseline yielding a sensitivity of 0.77 and specificity of 0.50 for predicting elongation of 10% or more at 1 y. Elongation of the Achilles tendon at baseline measured with CALM was weakly correlated to elongation at 1 y. A cut off of 7% elongation at baseline caught 77% of patients who, when treated nonsurgically, ended up with an elongation above 10% at 1 y. A prospective trial investigating CALM as part of a selection algorithm for deciding between operative and nonoperative treatment is needed.

Mechanical properties of muscles and tendon structures in middle-aged and young men

The purpose of this study was to compare the mechanical properties of muscles and tendon structures for plantar flexor muscles at various strain rates and jump performances using single joint between middle-aged and young men in order to clarify the mechanisms of age-related decline in power output during vertical jump of middle-aged people previously reported. Passive muscle stiffness of the medial gastrocnemius muscle was determined based on passive muscle force and fascicle length during passive stretching at four angular velocities. Active muscle stiffness was calculated based on changes in muscle force and fascicle length during stretching at five angular velocities after submaximal isometric contractions. Maximal elongation and hysteresis of tendon structures were assessed from estimated muscle force—tendon elongation during ramp and ballistic contractions. Two kinds of unilateral jump heights using only ankle joint (no-countermovement and countermovement jumps) were measured. No significant differences in passive and active muscle stiffness, tendon structure properties (except for maximal elongation during ramp contraction), or jump heights were found between middle-aged and young men. The results suggest that the mechanical properties of muscles and tendon structures for plantar flexor muscles and jump performances using only ankle joint do not show age-related changes in middle-aged men.

Triceps Surae Muscle-Tendon Properties as Determinants of the Metabolic Cost in Trained Long-Distance Runners.

Purpose: This study aimed to determine whether triceps surae’s muscle architecture and Achilles tendon parameters are related to running metabolic cost (C) in trained long-distance runners.Methods: Seventeen trained male recreational long-distance runners (mean age = 34 years) participated in this study. C was measured during submaximal steady-state running (5 min) at 12 and 16 km h–1 on a treadmill. Ultrasound was used to determine the gastrocnemius medialis (GM), gastrocnemius lateralis (GL), and soleus (SO) muscle architecture, including fascicle length (FL) and pennation angle (PA), and the Achilles tendon cross-sectional area (CSA), resting length and elongation as a function of plantar flexion torque during maximal voluntary plantar flexion. Achilles tendon mechanical (force, elongation, and stiffness) and material (stress, strain, and Young’s modulus) properties were determined. Stepwise multiple linear regressions were used to determine the relationship between independent variables (tendon resting length, CSA, force, elongation, stiffness, stress, strain, Young’s modulus, and FL and PA of triceps surae muscles) and C (J kg–1m–1) at 12 and 16 km h–1.Results: SO PA and Achilles tendon CSA were negatively associated with C (r2 = 0.69; p < 0.001) at 12 km h–1, whereas SO PA was negatively and Achilles tendon stress was positively associated with C (r2 = 0.63; p = 0.001) at 16 km h–1, respectively. Our results presented a small power, and the multiple linear regression’s cause-effect relation was limited due to the low sample size.Conclusion: For a given muscle length, greater SO PA, probably related to short muscle fibers and to a large physiological cross-sectional area, may be beneficial to C. Larger Achilles tendon CSA may determine a better force distribution per tendon area, thereby reducing tendon stress and C at submaximal speeds (12 and 16 km h–1). Furthermore, Achilles tendon morphological and mechanical properties (CSA, stress, and Young’s modulus) and triceps surae muscle architecture (GM PA, GM FL, SO PA, and SO FL) presented large correlations with C.

Transcriptomic and Genetic Analyses Identify the Krüppel-Like Factor Dar1 as a New Regulator of Tube-Shaped Long Tendon Development.

To ensure locomotion and body stability, the active role of muscle contractions relies on a stereotyped muscle pattern set in place during development. This muscle patterning requires a precise assembly of the muscle fibers with the skeleton via a specialized connective tissue, the tendon. Like in vertebrate limbs, Drosophila leg muscles make connections with specific long tendons that extend through different segments. During the leg disc development, cell precursors of long tendons rearrange and collectively migrate to form a tube-shaped structure. A specific developmental program underlies this unique feature of tendon-like cells in the Drosophila model. We provide for the first time a transcriptomic profile of leg tendon precursors through fluorescence-based cell sorting. From promising candidates, we identified the Krüppel-like factor Dar1 as a critical actor of leg tendon development. Specifically expressed in the leg tendon precursors, loss of dar1 disrupts actin-rich filopodia formation and tendon elongation. Our findings show that Dar1 acts downstream of Stripe and is required to set up the correct number of tendon progenitors.

Stretch-Shortening Cycle Performance and Muscle-Tendon Properties in Dancers and Runners.

The purpose of this investigation was to elucidate whether ankle joint stretch-shortening cycle performance, isometric and isokinetic plantarflexion strength, and maximal Achilles tendon force and elongation differ between dancers, endurance runners, and untrained controls. To differentiate between dancers, endurance runners, and controls, the authors measured maximal Achilles tendon force and elongation during isometric ramp contractions with ultrasonic imaging, maximal isometric and isokinetic plantarflexion strength with dynamometry, and stretch-shortening cycle function during countermovement hopping and 30-cm drop hopping with a custom-designed sled. The Achilles tendon of dancers elongated significantly (P ≤ .05) more than runners and controls. Dancers were significantly stronger than controls during isometric contractions at different ankle angles. Concentric and eccentric strength during isokinetic contractions at 60°·s-1 and 120°·s-1 was significantly higher in dancers and runners than controls. Dancers hopped significantly higher than runners and controls during hopping tasks. Dancers also possessed significantly greater countermovement hop relative peak power, drop hop relative impulse, and drop hop relative peak power than controls. Finally, dancers reached significantly greater velocities during countermovement hops than runners and controls. Our findings suggest dancing and running require or likely enhance plantarflexion strength. Furthermore, dancing appears to require and enhance ankle joint stretch-shortening cycle performance and tendon elongation.

Age-related structural changes show that loss of fibers is not a significant contributor to muscle atrophy in old mice.

Age-related loss of skeletal muscle mass is widely considered a consequence of both fiber atrophy and fiber death. Evidence for fiber death derives largely from an age-related reduction in fiber numbers in muscle cross-sections, however it is unclear how age-related alterations in muscle morphology affect accuracy of such counts. To explore this we performed an examination of muscle and tendon length, muscle mass and girth, and pennation angle, in addition to histological section fiber counts of parallel-fibered (sternomastoid), fusiform (biceps brachii), and pennate (tibialis anterior, extensor digitorum longus, soleus) muscles from 31 mice aged 6-32months. Age-related decline in mass and girth occurred in soleus (p=0.026; p=0.040), tibialis anterior (p=0.004; p=0.039), and extensor digitorum longus (p=0.040; p=0.022) muscles, for which location of maximal girth also changed. Tendon length and pennation angle remained consistent across the lifespan in all except soleus which showed elongation of both proximal and distal tendons coupled with alterations in pennation angle. Age-related decreases in fiber number were observed in transversely sectioned soleus and extensor digitorum longus muscles however when age-related changes in morphology were accounted for via oblique sectioning the age-related decrease in fiber number was eliminated. Findings show loss of fibers is not a significant contributor to age-related muscle wasting in mice, and that age-related changes in connective tissue selectively impact muscle structure. Fiber shortening is a likely contributor to loss of mass and change in function in muscles of old mice.