Achilles Tendon Mechanical Properties Research Articles

Differences in Achilles tendon mechanical properties between professional ballet dancers and collegiate athletes utilizing shear wave elastography.

To report normative stiffness parameters obtained using shear wave elastography in dorsiflexion from the Achilles tendons in asymptomatic professional ballet dancers and compare them with college-level athletes. An Institutional Review Board (IRB)-approved study consists of 28 professional ballet dancers and 64 asymptomatic collegiate athletes. The athletes were further subdivided into runner and non-runner disciplines. Shear wave elastography (SWE) measurements were made in maximum ankle dorsiflexion position. Forty-eight (52%) males and 44 (48%) females were examined with an overall mean age of 22.2 (± 3.8 years). There were no significant SWE differences between dominant and non-dominant legs in both groups and comparing spin vs. non-spin leg of ballet dancers (p > 0.05). Ballet dancers had significantly higher short-axis velocity values than runners and non-runners (2.34 m/s increase and 2.79 m/s increase, respectively, p < 0.001). Long-axis velocity was significantly higher in ballet dancers compared to non-runners (by 0.80 m/s, p < 0.001), but was not different between ballet dancers and runners (p > 0.05). Short-axis modulus was significantly higher in dancers compared to runners and non-runners (by 135.2 kPa and 159.2 kPa, respectively, p < 0.001). Long-axis modulus (LAM) was not significantly different in ballet dancers when compared to runners. Asymptomatic professional ballet dancers exhibit greater short-axis tendon stiffness compared to athletes and greater long-axis tendon stiffness compared to non-runners but similar to runners. The functional benefit from elevated short-axis stiffness in dancers is not clear but may be related to greater axial loading and adaptations of the tendon matrix.

MULTISCALE ASSESSMENT OF ACHILLES TENDON MECHANICS AND MECHANOBIOLOGY

Achilles tendon mechanical properties depend on a complex hierarchical design, with collagen being the smallest load-bearing unit. At the nanoscale, collagen molecules are organized into fibrils, which at the microscale are assembled into fibers, followed by larger structures such as sub-tendons or fascicles. Degree of in vivo loading affects the collagen content, and organization and consequently the tissue's mechanical response. We aim to unravel how composition, structural organization, and mechanical response are affected by degree of in vivo loading at each length scale. The presentation will outline the results to date about to the use of high-resolution synchrotron-based tissue characterisation methods on several length scales in combination with in situ mechanical tests. We use a rat model, where the tendons are subjected to varying loading in vivo. To characterize the tissue microstructure, phase-contrast enhanced synchrotron micro-tomography is performed. The 3D fiber organization in fully loaded tendons is highly aligned, whereas the fibers in unloaded tendons are significantly more heterogeneously arranged and crimped. To characterize the collagen fibril response, Small Angle X-ray Scattering is performed. Two types of fibril organizations are found; a single population oriented towards the main load direction and two fibril subpopulations with clearly distinct orientations. Scattering during loading showed that the fibrils in unloaded tendons did not strain as much in fully loaded. In situ loading concurrently with high resolution synchrotron experiments show the complex tendon response to in situ load and its relation to in vivo loading and tendon hierarchical structure. Unloading seems to alter the organization of the fibrils and fibers, e.g. increased crimping and more pronounced sub-tendon twists.Acknowledgements: Funding from Knut and Alice Wallenberg Foundation and European Research Council (101002516). Paul Scherrer Institut, Switzerland for beamtime at cSAXS and TOMCAT.

Effects of Collagen and Exercise on Tendon Properties and Pain: A Critically Appraised Topic.

Achilles tendon ruptures are prevalent and devastating injuries that require the need for extensive rehabilitation. The methods for preventing these injuries vary between different exercise methods and nutritional supplementation. Although proven effective for decreasing pain and increasing tendon properties, the influence of these 2 methods in combination has not yet been evaluated. Does exercise combined with collagen supplementation improve Achilles tendon structural and mechanical properties and diminish subsequent patient-reported pain compared with exercise alone in adults? Exercise training, including eccentric training protocols and concentric resistance training protocols, combined with collagen supplementation influence Achilles tendon properties and subsequent patient-reported pain compared with exercise alone. Evidence supports that collagen along with exercise training has a significant influence on pain mitigation, augmented cross-sectional area, and tendon thickness, but may have little to no influence on tendon stiffness and microvascularity compared with exercise alone. Further research is needed to determine the effects of combined methods on various populations. Collectively, the body of evidence included to answer the clinical question aligns with the strength of recommendation of A.

Reduction in postnatal weight-bearing does not alter the trajectory of murine meniscus growth and maturation.

The early postnatal period represents a critical window for the maturation and development of orthopedic tissues, including those within the knee joint. To understand how mechanical loading impacts the maturational trajectory of the meniscus and other tissues of the hindlimb, perturbation of postnatal weight bearing was achieved through surgical resection of the sciatic nerve in neonatal mice at 1 or 14 days old. Sciatic nerve resection (SNR) produced significant and persistent disruptions in gait, leading to reduced tibial length and reductions in Achilles tendon mechanical properties. However, SNR resulted in minimal disruptions in morphometric parameters of the menisci and other structures in the knee joint, with no detectable differences in Col1a1-YFP or Col2a1-CFP expressing cells within the menisci. Furthermore, micromechanical properties of the meniscus and cartilage (as assessed by atomic force microscopy-based nanoindentation testing) were not different between experimental groups. In contrast to our initial hypothesis, reduced hindlimb weight bearing via neonatal SNR did not significantly impact the growth and development of the knee meniscus. This unexpected finding demonstrates that the input mechanical threshold required to sustain meniscus development may be lower than previously hypothesized, though future studies incorporating skeletal kinematic models coupled with force plate measurements will be required to calculate the loads passing through the affected hindlimb and precisely define these thresholds. Collectively, these results provide insight into the mechanobiological responses of the meniscus to alterations in load, and contribute to our understanding of the factors that influence normal postnatal development.

Adolescent boys who participate in sports exhibit similar ramp torque control with young men despite differences in strength and tendon characteristics.

The goal of this paper was to determine if sports participation influences torque control differently for adolescent boys and young men during a slow ramp task. Twenty-one adolescent boys (11 athletes) and 31 young men (16 athletes) performed a slow ramp increase in plantar flexion torque from 0 to maximum. We quantified torque control as the coefficient of variation (CV) of torque during the ramp and quantified the Achilles tendon mechanical properties using ultrasonography. Relative to adolescent boys, young men were taller, heavier, stronger, and had a longer and stiffer Achilles tendon. However, these characteristics were not different between athletes and non-athletes in adolescent boys. For the CV of torque, there was a significant interaction with sports participation, indicating that only adolescent boys who were non-athletes had greater variability than young men. The CV of torque of all participants was predicted from the maximum torque and torque oscillations from 1 to 2Hz, whereas the CV of torque for adolescent boys was predicted only from torque oscillations from 1 to 2Hz. These findings suggested that adolescent boys who participate in sports exhibited lower torque variability during a slow ramp task, which was not explained by differences in Achilles tendon properties or strength.

Are the mechanical properties of Achilles tendon Altered in CrossFit athletes? Reliability and accuracy of myotonometry

Purpose Tendons adapt to loads affecting them, by changing tendons’ mechanical and morphological properties. The aim of the study has been to investigate the influence of involvement in sport activities in the form of CrossFit training by individuals of different age upon the mechanical properties of Achilles tendon. Methods 231 persons participated in the study. One group consisted of subjects who train CrossFit as amateurs, the other group comprised subjects who were not physically active. Achilles tendon was studied for various positions of the ankle joint: 0° DF/PF, 10° DF, 20° DF, 20° PF and 40° PF. The following mechanical and viscoelastic tendon properties were measured using MyotonPRO: frequency [Hz], stiffness [N/m], decrement [log], relaxation time [ms] and creep [De]. The results have been compared in reference to physical activity, BMI, age, and length of training history. Results Both the tension and stiffness increased with degree of Achilles tendon stretching and decreased as it contracted. Higher values have been noted in the group of people in training and with higher BMI values. The elasticity of Achilles tendon decreased with plantar flexion increase. Lower elasticity has been recorded in the group in training and with higher BMI. No significant influence of age and length of training history upon the parameters achieved has been noted. Conclusions The specificity of Crossfit training and accompanying mechanical load result in development of adaptation changes in Achilles tendon, in the form of its higher tone/tension and stiffness, as well as lower elasticity.

Achilles tendon mechanical properties during walking and running are underestimated when its curvature is not accounted for

Achilles tendon (AT) mechanical properties can be estimated using an inverse dynamic approach, taking into account the tendon internal moment arm (IMA) and its kinematic behavior. Although AT presents a curvilinear line of action, a straight-line function to estimate IMA and AT length is often utilized in the literature. In this study, we combined kinetic, kinematic and ultrasound data to understand the impact of two different approaches (straight-line vs. curvilinear) in determining AT mechanical properties in vivo (during walking and running at the self-selected speed). AT force and power were calculated based on data of AT IMA and AT length derived by both respective methods. All investigated parameters were significantly affected by the method utilized (paired t-test; p < 0.05): when using the curvilinear method IMA was about 5% lower and AT length about 1.2% higher, whereas peak and mean values of AT force and power were 5% higher when compared to the straight-line method (both in walking and running). Statistic-parametric mapping (SMP) analysis revealed significant differences in IMA during the early and the late stance phase of walking and during the late stance phase of running (p < 0.01); SPM revealed significant differences also in AT length during the entire stance phase in both locomotion modes (p < 0.01). These results confirm and extend previous findings to human locomotion: neglecting the AT curvature might be a source of error, resulting in underestimates not only of internal moment arm and tendon length, but also of tendon force and power.

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.

An Identical Twin Study on Human Achilles Tendon Adaptation: Regular Recreational Exercise at Comparatively Low Intensities Can Increase Tendon Stiffness

Achilles tendon adaptation is a key aspect of exercise performance and injury risk prevention. However, much debate exists about the adaptation of the Achilles tendon in response to exercise activities. Most published research is currently limited to elite athletes and selected exercise activities. Also, existing studies on tendon adaptation do not control for genetic variation. Our explorative cross-sectional study investigated the effects of regular recreational exercise activities on Achilles tendon mechanical properties in 40 identical twin pairs. Using a handheld oscillation device to determine Achilles tendon mechanical properties, we found that the Achilles tendon appears to adapt to regular recreational exercise at comparatively low intensities by increasing its stiffness. Active twins showed a 28% greater Achilles tendon stiffness than their inactive twin (p < 0.05). Further, our research extends existing ideas on sport-specific adaptation by showing that tendon stiffness seemed to respond more to exercise activities that included an aerial phase such as running and jumping. Interestingly, the comparison of twin pairs revealed a high variation of Achilles tendon stiffness (305.4–889.8 N/m), and tendon adaptation was only revealed when we controlled for genetic variance. Those results offer new insights into the impact of genetic variation on individual Achilles tendon stiffness, which should be addressed more closely in future studies.

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.

Ultrasound Stress-Imaging is a Promising Tool to Detect Achilles Tendon Damage

Category:Sports; Basic Sciences/BiologicsIntroduction/Purpose:Achilles tendon disorders are among the most common conditions observed by sports medicine physicians and among the most difficult to diagnose using current clinical tools. While qualitative imaging is a validated method to grade the severity of tendinopathy, predicting the risk of these patients progressing or suffering tendon ruptures remains a major clinical need. Therefore, the purpose of this study was to determine the efficacy of quantitative ultrasound imaging to explain in vitro fatigue-induced degradation of Achilles tendon mechanical properties. We hypothesized that decreases in mean echogenicity would be linked to in vitro tendon fatigue characterized by decreased mechanical properties.Methods:In this cadaveric tendon study, we cyclically fatigued 10 cadaveric Achilles tendons (7 donors; sex: 4M, 3F; age: 60+-15 years) and acquired b-mode ultrasound images to determine if stress-imaging biomarkers provide new insight into tendon status. We cut dog-bone shapes to concentrate tendon damage at the mid-substance where we acquired ultrasound images. In a custom- built testing bath, we cyclically applied 10-20 MPa of tendon stress at 1 Hz for 150,00 or until the specimen failed. Every 500th cycle, we applied 2 slow (0.25 Hz) tendon stresses of 10-20 MPa while acquiring ultrasound images using an 18MHz transducer.We calculated the change in tendon echogenicity caused by the applied stress to determine if this stress-imaging biomarker was associated with tendon failure. We compared these stress-imaging biomarkers from the tendons that failed (N=6) and the tendons that survived (N=4) cyclic fatigue damage using an unpaired t-test (p < 0.05).Results:Quantitative analysis of the ultrasound images indicated 2 key differences between tendons that failed during the cyclic loading protocol and those that did not (Figure 1 shows representative data of tendons with similar demographics but one tendon exhibited increased change in echogenicity before failing while the other tendon exhibited smaller changes in echogenicity and did not rupture). First, mean echogenicity decreased before failure. Second, the average change in mean echogenicity was significantly greater in tendons that failed (p = 0.031). For most tendons that did fail, mean echogenicity decreased during the third phase of fatigue life. For the tendons that did not fail, mean echogenicity plateaued along with strain during the second phase of fatigue.Conclusion:This study found detectable differences in image echogenicity during a stress test between tendons that fail during cyclic loading and those that do not. While preliminary, our findings indicate that B-mode ultrasound has potential as a clinically viable tool to predict severe tendon injuries. Our future work is focused on developing computer-based predictive tools to assess Achilles tendon fatigue in patients with tendinopathy following prolonged tendon loading to establish quantitative imaging thresholds that can serve as clinical benchmarks.

Achilles Tendon Ruptures in Middle-Aged Rats Heal Poorly Compared With Those in Young and Old Rats

Background: Achilles tendon ruptures are painful and debilitating injuries and are most common in middle-aged patients. There is a lack of understanding of the underlying causes for increased rupture rates in middle-aged patients and how healing outcomes after a rupture might be affected by patient age. Therefore, the objective of this study was to define age-specific Achilles tendon healing by assessing ankle functional outcomes and Achilles tendon mechanical and histological properties after a rupture using a rat model. Hypothesis: Rats representing the middle-aged patient population would demonstrate reduced healing capability after an Achilles tendon rupture, as demonstrated by a slower return to baseline ankle functional properties and inferior biomechanical and histological tendon properties. Study Design: Controlled laboratory study. Methods: Fischer 344 rats were categorized by age to represent young, middle-aged, and old patients, and Achilles tendon ruptures were induced in the right hindlimb. Animals were allowed to heal and were euthanized at 3 or 6 weeks after the injury. In vivo functional assays and ultrasound imaging were performed throughout the healing period, and ex vivo tendon mechanical and histological properties were assessed after euthanasia. Results: Rats representing middle-aged patients displayed reduced healing potential compared with the other age groups, as they demonstrated decreased recovery of in vivo functional and ultrasound assessment parameters and inferior mechanical and histological properties after an Achilles tendon rupture. Conclusion: These findings may help explain the increased rupture rate observed clinically in middle-aged patients by suggesting that there may be altered tendon responses to daily trauma. Clinical Relevance: The results provide novel data on age-specific healing outcomes after an Achilles tendon rupture, which underscores the importance of considering a patient’s age during treatment and expectations for outcomes.

Sex Differences in the Morphological and Mechanical Properties of the Achilles Tendon.

Background: Patients with Achilles tendon (AT) injuries are often engaged in sedentary work because of decreasing tendon vascularisation. Furthermore, men are more likely to be exposed to AT tendinosis or ruptures. These conditions are related to the morphological and mechanical properties of AT, but the mechanism remains unclear. This study aimed to investigate the effects of sex on the morphological and mechanical properties of the AT in inactive individuals. Methods: In total, 30 inactive healthy participants (15 male participants and 15 female participants) were recruited. The AT morphological properties (cross-sectional area, thickness, and length) were captured by using an ultrasound device. The AT force–elongation characteristics were determined during isometric plantarflexion with the ultrasonic videos. The AT stiffness was determined at 50%–100% maximum voluntary contraction force. The AT strain, stress, and hysteresis were calculated. Results: Male participants had 15% longer AT length, 31% larger AT cross-sectional area and 21% thicker AT than female participants (p < 0.05). The plantarflexion torque, peak AT force, peak AT stress, and AT stiffness were significantly greater in male participants than in female participants (p < 0.05). However, no significant sex-specific differences were observed in peak AT strain and hysteresis (p > 0.05). Conclusions: In physically inactive adults, the morphological properties of AT were superior in men but were exposed to higher stress conditions. Moreover, no significant sex-specific differences were observed in peak AT strain and hysteresis, indicating that the AT of males did not store and return elastic energy more efficiently than that of females. Thus, the mechanical properties of the AT should be maintained and/or improved through physical exercise.

Bilateral in vivo neuromechanical properties of the triceps surae and Achilles tendon in runners and triathletes

Inter-limb differences in Achilles tendon mechanical, material and morphological properties have previously been described in non-athletes and attributed to the preferential use of a given limb. Achilles tendon overuse tendon injury generally initiate unilaterally and alters triceps surae activation and Achilles tendon properties. The investigation of inter-limb differences in muscle activation and tendon properties may provide directions for injury prevention in habitual runners. In this study triceps surae and Achilles tendon properties were investigated bilaterally in habitual runners during unilateral maximal isometric contractions. Morphological, mechanical and material Achilles tendon properties were assessed using isokinetic dynamometry, motion capture and ultrasonography while triceps surae activation strategies were assessed using electromyography. Lower limb preference was assessed for inter-limb comparisons using the Waterloo questionnaire. Zero and one-dimensional statistical analysis and Cohen’s d were employed to investigate possible inter-limb differences. Inter-limb associations in Achilles tendon properties and intra-limb associations between triceps surae activations were assessed using Pearson’s correlation coefficients. No differences were observed between the preferred and non-preferred limb in terms of triceps surae muscle activation amplitude and Achilles tendon properties. However, intra-limb association among triceps surae activation ratios were not identical between limbs. Runners and triathletes present similar Achilles tendons properties between limbs, and thus initial observations of unilateral changes in the Achilles tendon properties might be used as a strategy to prevent the onset of overuse tendon injury. The non-similar associations within activation ratios between limbs should be further explored since triceps surae activation strategies may alter loading of the Achilles tendon.

An adaptive Model of Achilles Tendon Mechanical Properties during Adolescence: Effect of Sex

An adaptive Model of Achilles Tendon Mechanical Properties during Adolescence: Effect of Sex

The differences in viscoelastic properties of subtendons result from the anatomical tripartite structure of human Achilles tendon - ex vivo experimental study and modeling

The human Achilles tendon (AT) is a hierarchical structure macroscopically composed of three subtendons originating from the soleus (SOL) and gastrocnemius (GL, GM) muscles. According to recent reports, the divisible structure of the AT together with diverse material properties of its subtendons are suspected as a probable cause of non-homogeneous stress and strain distribution occurring in loaded AT. Despite numerous investigations on human AT, there is still relatively little knowledge regarding mechanical properties of subtendon-level hierarchy, which is crucial in fully understanding the multiscale relationship which governs tendon mechanics.In this paper we present the first ex vivo study conducted on SOL, GL, and GM subtendons of human AT. We investigate differences in viscoelastic properties of SOL, GM, and GL subtendons in terms of tensile modulus, mechanical hysteresis as well as stress relaxation observed at two different values of strain. Our results show that the most significant differences in mechanical properties exist between subtendon attached to the soleus muscle (SOL) and subtendons originating from the two heads of the gastrocnemius muscle (GM and GL). We used our experimental results to calibrate three different constitutive models: the hyperelastic Yeoh model with power-law flow, the microstructurally motivated Holzapfel-Gasser-Ogden model enhanced with strain-dependent Berström-Boyce flow and the phenomenological elasto-viscoplastic Arruda-Boyce-based model with strain-dependent Berström-Boyce flow supplemented with component representing matrix response. All calibrated models may be applied to commercial FEA software as a sufficient solution for rapid mechanical response modeling of human AT subtendons or for the purpose of future development of comprehensive patient-specific models of human lower limbs. Statement of significanceThe divisible structure of the Achilles tendon together with diverse material properties of its subtendons are suspected as a probable cause of non-homogeneous stress and strain distribution occurring in loaded Achilles tendon. Despite numerous investigations on mechanical properties of Achilles tendon, there is still relatively little knowledge regarding mechanical properties of subtendon-level hierarchy, which is crucial in fully understanding the multiscale relationship which governs tendon mechanics. This study is the first reported ex vivo investigation conducted on SOL, GL, and GM human Achilles subtendons. We investigate differences in the viscoelastic properties of individual subtendons and demonstrate that the observed differences should be considered as muscle-dependent. Our experimental research is supported with a modeling study in which we calibrate three different constitutive models.

Shear wave and strain sonoelastography for the evaluation of the Achilles tendon during isometric contractions

ObjectivesChanges in mechanical loading as well as pathology can modify the Achilles tendon mechanical properties and therefore detection of these changes is relevant for the diagnosis and management of Achilles tendinopathy. The aim of this study was to evaluate strain and shear wave sonoelastography for their ability to detect changes in the Achilles tendon mechanical properties during a series of isometric contractions.MethodsLongitudinal sonoelastography images of the Achilles tendon were acquired from 20 healthy participants using four different ultrasound devices; two implementing strain sonoelastography technology (SE1, SE2) and two, shear wave elastography technology (SWE1, SWE2).ResultsSE1 measured a decreasing strain ratio (tendon become harder) during the different contraction levels from 1.51 (0.92) to 0.33 (0.16) whereas SE2 mesaured a decreasing strain ratio from 1.08 (0.76) to 0.50 (0.32). SWE1 measured decreasing tendon stiffness during contractions of increasing intensity from 33.40 (19.61) to 16.19 (2.68) whereas SWE2 revealed increasing tendon stiffness between the first two contraction levels from 428.65 (131.5) kPa to 487.9 (121.5) kPa followed by decreasing stiffness for the higher contraction levels from 459.35 (113.48) kPa to 293.5 (91.18) kPa.ConclusionsStrain elastography used with a reference material was able to detect elasticity changes between the different contraction levels whereas shear wave elastography was less able to detect changes in Achilles tendon stiffness when under load. Inconsistent results between the two technologies should be further investigated.

Motor Control and Achilles Tendon Adaptation in Adolescence: Effects of Sport Participation and Maturity.

An important but unresolved research question in adolescent children is the following: “Does sport participation interact with maturation to change motor control and the mechanical and morphological properties of tendons?” Here, we address this important research question with a longitudinal study around the age of peak height velocity (PHV). Our purpose was to characterize the interactive effects of maturation and sports participation on motor control and the mechanical and morphological properties of the Achilles tendon (AT) in adolescent athletes and non-athletes. Twenty-two adolescent athletes (13.1 ± 1.1 years) and 19 adolescent non-athletes (12.8 ± 1.1 years) volunteered for this study. We quantified motor control as the coefficient of variation of torque during a ramp task. In addition, we quantified the AT morphological and mechanical properties using ultrasonography from 18 months before to 12 months after PHV. We found that motor control improved with maturation in both athletes and non-athletes. We found that athletes have a greater increase in body mass with maturation that relates to greater plantarflexion peak force and AT peak stress. Also, athletes have a thicker and longer AT, as assessed with resting cross-sectional area and length. Although the rate of increase in the morphological change with maturation was similar for athletes and non-athletes, the rate of increase in normalized AT stiffness was greater for athletes. This increased AT stiffness in athletes related to peak force and stress. In summary, maturation improves motor control in adolescent children. Further, we provide novel longitudinal evidence that sport participation interacts with maturation in adolescents to induce adaptive effects on the Achilles tendon morphology and mechanical properties. These findings have the potential to minimize the risk of injuries and maximize athletic development in talented adolescents.

Coordination variability in runners after surgical Achilles tendon repair

The purpose of this study was to compare lower extremity coordination variability between runners with history of Achilles tendon rupture and healthy controls. Twenty participants, 10 Achilles tendons repaired and 10 controls, were recruited. The groups were matched according to age, sex, volume of running, speed, body mass, height, and footfall type. Achilles tendon mechanical properties were determined using a sonographic technique. A motion capture system was used to record running kinematics. A vector coding technique was used to investigate segment coordination variability and the mean phase angle. Statistical parametric mapping was used to examine the relationship in coordination variability between groups. Higher foot eversion and shank internal rotation coordination variability were found in participants with a history of Achilles tendon rupture compared to healthy controls during the portion of the stance phase between 47.2% and 50.3% when the maximal ground reaction force occurs. The current study provides the empirical evidence for increased coordination variability in a specifically affected group of runners. Altered coordination variability between the foot and shank may indicate a risk of abnormal loading of the musculoskeletal structures of the lower extremity in runners with a history of Achilles tendon rupture.

Contribution of Achilles tendon mechanical properties to torque steadiness in persons with transfemoral amputation.

How Achilles tendon mechanics and plantar flexion strength and torque steadiness are altered in the intact leg of persons with trauma-related amputation is unknown. Understanding Achilles tendon mechanics following amputation will further inform rehabilitation approaches to enhance posture, balance, and force control. Conduct a pilot study to quantify plantar flexion maximal voluntary contraction torque, torque steadiness, and Achilles tendon mechanics in persons with unilateral trauma-related transfemoral amputation and controls without amputation. Cross-sectional study. Isometric plantar flexion maximal voluntary contractions were performed with the intact leg of ten males with transfemoral amputation (48 ± 14 years) and the dominant leg of age-matched male controls without amputation. Torque steadiness was calculated as the coefficient of variation in torque over 6 s during submaximal tracking tasks (5%, 10%, 25%, 50%, and 75% maximal voluntary contraction). Achilles tendon elongation and cross-sectional area were recorded with ultrasound to calculate strain, stress, and stiffness. Maximal voluntary contraction and torque steadiness did not differ between persons with amputation (90.6 ± 31.6 N m, 3.7 ± 2.0%) and controls (95.8 ± 26.8 N m, 2.9 ± 1.2%; p > 0.05). Tendon stiffness (21.1 ± 18.2 N/mm) and strain (5.2 ± 1.3%) did not differ between groups (p > 0.05). Tendon cross-sectional area was 10% greater in persons with amputation leading to 29% lower stress (p = 0.021). Maximal voluntary contraction was a predictor of a lower coefficient of variation in torque (R2 = 0.11, p < 0.05). Persons with trauma-related transfemoral amputation do not differ in plantar flexion maximal voluntary contraction and torque steadiness of the intact leg compared with controls without amputation. Larger tendon cross-sectional area reduces stress and enables distribution of force across a greater area.