Tendon Geometry Research Articles

Measuring Ultrasonographic Thickness of the Achilles Tendon Insertion Is Less Reliable Than the Midportion in Healthy Tendons and Patients With Tendinopathy.

Ultrasound is the preferred imaging method in the diagnostic process of Achilles tendinopathy (AT). Ultrasound tissue characterization (UTC) is a frequently used, standardized and valid method to assess tendon geometry in AT patients. It is unknown whether UTC is reliable for measuring Achilles tendon thickness. The aim of the study was to assess intra- and inter-rater reliability of Achilles tendon thickness measurements using UTC in both asymptomatic individuals and patients with AT, and to evaluate if the reliability of thickness measurements differs between the midportion and insertional area. Exactly 50 patients with AT and 50 asymptomatic individuals were included. Using the conventional US and standardized UTC procedure maximum thickness was measured in the midportion and insertion region. To determine inter- and intra-rater reliabilities, the intraclass correlation coefficient (ICC) was used. The ICC values for inter- and intra-rater reliability were classified as "excellent," for the AT group (0.93 [95% CI: 0.88-0.96] and 0.95 [0.92-0.97]) and asymptomatic participants (0.91 [0.87-0.94] and 0.94 [0.92-0.96]). The reliability of measuring tendon thickness in the midportion region was "excellent," with both inter-rater (0.97 [0.95-0.98]) and intra-rater (0.98 [0.96-0.99]) ICC values indicating high levels of agreement. In the insertional region, ICC values for inter-rater (0.79 [0.69-0.87]) and intra-rater (0.89 [0.84-0.93]) reliability were "moderate to good." We showed excellent reliability for measuring the US thickness of the midportion and good reliability of measuring the insertional region in patients with AT. Significantly lower ICCs were observed for the reliability of thickness measurements in the insertional region when compared with the midportion.

Estimation of the Effects of Achilles Tendon Geometry on the Magnitude and Distribution of Local Strain: A Finite Element Analysis

We investigated the influence of Achilles tendon (AT) geometry on local-strain magnitude and distribution during loading, using finite element analysis. We calculated the following eight AT parameters for 18 healthy men: thickness and width of the most distal part, minimum cross-sectional area (mCSA), and most proximal part; length; and position of the mCSA. To investigate the effect of AT geometry on the magnitude and distribution of local strain, we created three-dimensional numerical models by changing the AT parameter values for every one standard deviation (SD) in the range of ±2 SD. A 4000 N lengthening force was applied to the proximal surface of all the models. The mean first principal strain (FPS) was determined every 3% of the length. The highest FPS in each model was mainly observed in the proximal regions; the 86–89% site (the most proximal site was set at 100%) had the highest number of models with the highest FPS (nine models). The highest FPS was observed in the model with a distal thickness of −2 SD, which was 27.1% higher than that of the standard model observed in the 2–5% site. Therefore, the AT geometry influences local-strain magnitude and distribution during loading.

Are subject-specific models necessary to predict patellar tendon fatigue life? A finite element modelling study

Patellar tendinopathy is an overuse injury that occurs from repetitive loading of the patellar tendon in a scenario resembling that of mechanical fatigue. As such, fatigue-life estimates provide a quantifiable approach to assess tendinopathy risk and may be tabulated using nominal strain (NS) or finite element (FE) models with varied subject-specificity. We compared patellar tendon fatigue-life estimates from NS and FE models of twenty-nine athletes performing countermovement jumps with subject-specific versus generic geometry and material properties. Subject-specific patellar tendon material properties and geometry were obtained using a data collection protocol of dynamometry, ultrasound, and magnetic resonance imaging. Three FE models were created for each subject, with: subject-specific (hyperelastic) material properties and geometry, subject-specific material properties and generic geometry, and generic material properties and subject-specific geometry. Four NS models were created for each subject, with: subject-specific (linear elastic) material properties and moment arm, generic material properties and subject-specific moment arm, subject-specific material properties and generic moment arm, and generic material properties and moment arm. NS- and FE-modelled fatigue-life estimates with generic material properties were poorly correlated with their subject-specific counterparts (r2 ≤0.073), while all NS models overestimated fatigue life compared to the subject-specific FE model (r2 ≤0.223). Furthermore, FE models with generic tendon geometry were unable to accurately represent the heterogeneous strain distributions found in the subject-specific FE models or those with generic material properties. These findings illustrate the importance of incorporating subject-specific material properties and FE-modelled strain distributions into fatigue-life estimations.

Individual variation in Achilles tendon morphology and geometry changes susceptibility to injury.

The unique structure of the Achilles tendon, combining three smaller sub-tendons, enhances movement efficiency by allowing individual control from connected muscles. This requires compliant interfaces between sub-tendons, but compliance decreases with age and may account for increased injury frequency. Current understanding of sub-tendon sliding and its role in the whole Achilles tendon function is limited. Here we show changing the degree of sliding greatly affects the tendon mechanical behaviour. Our in vitro testing discovered distinct sub-tendon mechanical properties in keeping with their mechanical demands. In silico study based on measured properties, subject-specific tendon geometry, and modified sliding capacity demonstrated age-related displacement reduction similar to our in vivo ultrasonography measurements. Peak stress magnitude and distribution within the whole Achilles tendon are affected by individual tendon geometries, the sliding capacity between sub-tendons, and different muscle loading conditions. These results suggest clinical possibilities to identify patients at risk and design personalised rehabilitation protocols.

3D Models Reveal the Influence of Achilles Subtendon Twist on Strain and Energy Storage.

The Achilles tendon (AT) has complex function in walking, exchanging energy due to loading by the triceps surae muscles. AT structure comprises three subtendons which exhibit variable twist among themselves and between individuals. Our goal was to create 3D finite element (FE) models to explore AT structure-function relationships. By simulating subtendon loading in FE models with different twisted geometries, we investigated how anatomical variation in twisted tendon geometry impacts fascicle lengths, strains, and energy storage. Three tendon FE models, built with elliptical cross sections based on average cadaver measurements, were divided into subtendons with varied geometric twist (low, medium, and high) and equal proportions. Tendon was modeled as transversely isotropic with fascicle directions defined using Laplacian flow simulations, producing fascicle twist. Prescribed forces, representing AT loading during walking, were applied to proximal subtendon ends, with distal ends fixed, and tuned to produce equal tendon elongation in each case, consistent with ultrasound measurements. Subtendon fascicle lengths were greater than free tendon lengths in all models by 1–3.2 mm, and were longer with greater subtendon twist with differences of 1.2–1.9 mm from low to high twist. Subtendon along-fiber strains were lower with greater twist with differences of 1.4–2.6%, and all were less than free tendon longitudinal strain by 2–5.5%. Energy stored in the AT was also lower with greater twist with differences of 1.8–2.4 J. With greater subtendon twist, similar elongation of the AT results in lower tissue strains and forces, so that longitudinal stiffness of the AT is effectively decreased, demonstrating how tendon structure influences mechanical behavior.

Tendon Geometry Optimization Using Path Integrals

The implementation of post-tensioned elements in concrete structures offers a multitude of benefits with regards to the overall structural behavior, with the efficacy of the applied tendons depending heavily on their geometry. However, the derivation of an optimal tendon geometry for a given structure is nontrivial, requiring engineering experience or the use of complex and often computationally demanding methodologies, e.g.the use of topology optimization strategies. This paper aims to investigate the possibility for optimizing tendon geometries using a path integral based objective function developed at the TU Berlin. For this purpose, the mathematical background is first presented to illustrate the proposed concept. Beginning with a tendon geometry optimization of a simply supported beam and progressing to more complex systems, a generalized approach for doubly curved spatial structures will be presented.

The Free Achilles Tendon Is Shorter, Stiffer, Has Larger Cross-Sectional Area and Longer T2* Relaxation Time in Trained Middle-Distance Runners Compared to Healthy Controls

Tendon geometry and tissue properties are important determinants of tendon function and injury risk and are altered in response to ageing, disease, and physical activity levels. The purpose of this study was to compare free Achilles tendon geometry and mechanical properties between trained elite/sub-elite middle-distance runners and a healthy control group. Magnetic resonance imaging (MRI) was used to measure free Achilles tendon volume, length, average cross-sectional area (CSA), regional CSA, moment arm, and T2* relaxation time at rest, while freehand three-dimensional ultrasound (3DUS) was used to quantify free Achilles tendon mechanical stiffness, Young’s modulus, and length normalised mechanical stiffness. The free Achilles tendon in trained runners was significantly shorter and the average and regional CSA (distal end) were significantly larger compared to the control group. Mechanical stiffness of the free Achilles tendon was also significantly higher in trained runners compared to controls, which was explained by the group differences in tendon CSA and length. T2* relaxation time was significantly longer in trained middle-distance runners when compared to healthy controls. There was no relationship between T2* relaxation time and Young’s modulus. The longer T2* relaxation time in trained runners may be indicative of accumulated damage, disorganised collagen, and increased water content in the free Achilles tendon. A short free Achilles tendon with large CSA and higher mechanical stiffness may enable trained runners to rapidly transfer high muscle forces and possibly reduce the risk of tendon damage from mechanical fatigue.

Association between increased signal intensity at the proximal patellar tendon and patellofemoral geometry in community-based asymptomatic middle-aged adults: a cross-sectional study

BackgroundHistological and epidemiological data suggest that increased signal intensity at the proximal patellar tendon on magnetic resonance imaging is a response to tendon loading. As patellofemoral geometry is a mediator of loading, we examined the association between patellofemoral geometry and the prevalence of increased signal intensity at the patellar tendon in community-based middle-aged adults.MethodsTwo hundred-one adults aged 25–60 years in a study of obesity and musculoskeletal health had the patellar tendon assessed from magnetic resonance imaging. Increased signal intensity at the proximal patellar tendon was defined as hyper-intense regions of characteristic pattern, size and distribution on both T1- and T2-weighted sequences. Indices of patellofemoral geometry, including Insall-Salvati ratio, patellofemoral congruence angle, sulcus angle, and lateral condyle-patella angle, were measured from magnetic resonance imaging using validated methods. Binary logistic regression was used to examine the association between patellofemoral geometrical indices and the prevalence of increased signal intensity at the patellar tendon.ResultsThe prevalence of increased signal intensity at the patellar tendon was 37.3%. A greater Insall-Salvati ratio (odds ratio 0.80, 95% confidence interval 0.66–0.97 per 0.1 change in the ratio, p = 0.02), indicative of a higher-riding patella, and a larger patellofemoral congruence angle (odds ratio 0.91, 95% confidence interval 0.85–0.98 per 5 degree change in the angle, p = 0.01), indicating a more laterally placed patella, were associated with reduced odds of increased signal intensity at the patellar tendon. Sulcus angle and lateral condyle-patella angle were not significantly associated with the odds of increased signal intensity at the patellar tendon.ConclusionsIn community-based asymptomatic middle-aged adults, increased signal intensity at the patellar tendon was common and associated with Insall-Salvati ratio and patellofemoral congruence angle, suggesting a biomechanical mechanism. Such work is likely to inform tissue engineering and cell regeneration approaches to improving outcomes in those with tendon pathology.

Targeted Achilles Tendon Training and Rehabilitation Using Personalized and Real-Time Multiscale Models of the Neuromusculoskeletal System.

Musculoskeletal tissues, including tendons, are sensitive to their mechanical environment, with both excessive and insufficient loading resulting in reduced tissue strength. Tendons appear to be particularly sensitive to mechanical strain magnitude, and there appears to be an optimal range of tendon strain that results in the greatest positive tendon adaptation. At present, there are no tools that allow localized tendon strain to be measured or estimated in training or a clinical environment. In this paper, we first review the current literature regarding Achilles tendon adaptation, providing an overview of the individual technologies that so far have been used in isolation to understand in vivo Achilles tendon mechanics, including 3D tendon imaging, motion capture, personalized neuromusculoskeletal rigid body models, and finite element models. We then describe how these technologies can be integrated in a novel framework to provide real-time feedback of localized Achilles tendon strain during dynamic motor tasks. In a proof of concept application, Achilles tendon localized strains were calculated in real-time for a single subject during walking, single leg hopping, and eccentric heel drop. Data was processed at 250 Hz and streamed on a smartphone for visualization. Achilles tendon peak localized strains ranged from ∼3 to ∼11% for walking, ∼5 to ∼15% during single leg hop, and ∼2 to ∼9% during single eccentric leg heel drop, overall showing large strain variation within the tendon. Our integrated framework connects, across size scales, knowledge from isolated tendons and whole-body biomechanics, and offers a new approach to Achilles tendon rehabilitation and training. A key feature is personalization of model components, such as tendon geometry, material properties, muscle geometry, muscle-tendon paths, moment arms, muscle activation, and movement patterns, all of which have the potential to affect tendon strain estimates. Model personalization is important because tendon strain can differ substantially between individuals performing the same exercise due to inter-individual differences in these model components.

A Validated, Specimen-Specific Finite Element Model of the Supraspinatus Tendon Mechanical Environment.

Rotator cuff tears are a significant clinical problem previously investigated by unvalidated computational models that either use simplified geometry or isotropic elastic material properties to represent the tendon. The objective of this study was to develop an experimentally validated, finite element model of supraspinatus tendon using specimen-specific geometry and inhomogeneous material properties to predict strains in intact supraspinatus tendon at multiple abduction angles. Three-dimensional tendon surface strains were determined at 60 deg, 70 deg, and 90 deg of glenohumeral abduction for articular and bursal surfaces of supraspinatus tendon during cyclic loading (5-200 N, 50 cycles, 20 mm/min) to serve as validation data for computational model predictions. A finite element model was developed using the tendon geometry and inhomogeneous material properties to predict surface strains for loading conditions mimicking experimental loading conditions. Experimental strains were directly compared with computational model predictions to validate the model. Overall, the model successfully predicted magnitudes of strains that were within the experimental repeatability of 3% strain of experimental measures on both surfaces of the tendon. Model predictions and experiments showed the largest strains to be located on the articular surface (∼8% strain) between the middle and the anterior edge of the tendon. Importantly, the reference configuration chosen to calculate strains had a significant effect on strain calculations, and therefore, must be defined with an innovative optimization algorithm. This study establishes a rigorously validated specimen-specific (both geometry and material properties) computational model using novel surface strain measurements for the use in investigating the function of the supraspinatus tendon and to ultimately predict the propagation of supraspinatus tendon tears based on the tendon's mechanical environment.

Partial Patellar Tendon Tears in Athletes: When Is Surgery Required?

Objectives: Partial patellar tendon tears (PPTTs) can be a frustrating injury for athletes and physicians. Determining the location and size of the PPTT are fundamental in understanding prognosis and selecting the most effective treatment. With recent enhancements in MRI quality, the size and dimensions of the tear can be more easily and accurately estimated. While some PPTTs respond to therapy, medication, bracing, biologic injections, and/or ultrasound procedures, other PPTTs in do not respond and require surgical intervention. The goal of this study is to correlate PPTT size and location to clinical outcomes, in order to create a classification system to help guide treatment decisions for athletes with PPTT. Methods: 112 athletic patients (range: 15-45 y/o, mean 23.9+7.2 y/o) who underwent knee MRI were included in this study. 85 of those patients (mean 24.9+8.1 y/o) presented with history and physical examination concerning for recalcitrant patellar tendonitis or suspicion of a partial patellar tendon tear. The other 27 athletic patients (mean 25.6+6.3 y/o) underwent MRI for other pathology and were included as age-matched controls. MR scans were evaluated for patellar tendon tear size, thickness, and location with respect to the entire patellar tendon. Descriptive statistics were used to evaluate tendon size and tear distributions. Pearson correlation, univariate regressions, and logistic regression were performed to correlate tendon geometry and tear sizes. Tear geometry variables were compared to patient outcome measures (return to previous activity level, surgical treatment) using t-tests. Results: 56 out of 85 symptomatic patients had partial patellar tendon tears. 91% of PPTTs involved the posterior and posteromedial region of the proximal patellar tendon (Figure 1). On axial MRI imaging, patients with PPTT had mean tendon thickness of 10 mm compared to 5.9 mm for athletes with no PPTT, including healthy controls (p<.0001). There was a significant correlation between patellar tendon thickness and PPTT size (R=0.85, p<0.0001). Logistic regression analysis showed that athletes with patellar tendon thickness above 7.45 mm are likely to have PPTTs (100% sensitivity). Tear distributions according to MRI grading are shown in Table 1. 11 out of 56 patients underwent surgery for PPTT. All 11 of these patients had tear sizes on axial images > 50% of tendon thickness (mean thickness of tear 6.3 mm). Logistic regression showed that patellar tendon thickness > 8.8 mm, and/or tear size > 55% correlated with surgical intervention. Five of the surgical patients did not make a return to sport at the same level. No patient in this series had surgery for tear thickness less than 4.5 mm. Basketball, track and field and soccer were the most common sports involved in the study. Conclusion: PPTTs are located posterior/posteromedially in the proximal patellar tendon. The most sensitive metric for PPTTs are patellar tendon thickness (anterior to posterior), where thickness more than 8.8 mm is strongly predictive of having a partial tear in the tendon. Athletes with greater than a 55% tear thickness on axial MRI imaging or with a tear measuring more than 4.5 mm on axial cuts are less likely to respond to non-operative treatment. Tracking thickness changes on axial views, specifically in the posterior/posteromedial region, may predict effectiveness of non-operative therapy. [Table: see text][Figure: see text]

Ontogenetic scaling of pelvic limb muscles, tendons and locomotor economy in the ostrich (Struthio camelus).

In rapidly growing animals there are numerous selective pressures and developmental constraints underpinning the ontogenetic development of muscle-tendon morphology and mechanical properties. Muscle force generating capacity, tendon stiffness, elastic energy storage capacity and efficiency were calculated from muscle and tendon morphological parameters and in vitro tendon mechanical properties obtained from a growth series of ostrich cadavers. Ontogenetic scaling relationships were established using reduced major axis regression analysis. Ostrich pelvic limb muscle mass and cross-sectional area broadly scaled with positive allometry, indicating maintained or relatively greater capacity for maximum isometric force generation in larger animals. The length of distal limb tendons was found to scale with positive allometry in several tendons associated with antigravity support and elastic energy storage during locomotion. Distal limb tendon stiffness scaled with negative allometry with respect to body mass, with tendons being relatively more compliant in larger birds. Tendon material properties also appeared to be size-dependent, suggesting that the relative increased compliance of tendons in larger ostriches is due in part to compensatory distortions in tendon material properties during maturation and development, not simply from ontogenetic changes in tendon geometry. Our results suggest that the previously reported increase in locomotor economy through ontogeny in the ostrich is due to greater potential for elastic energy storage with increasing body size. In fact, the rate of this increase may be somewhat greater than the conservative predictions of previous studies, thus illustrating the biological importance of elastic tendon structures in adult ostriches.

Side-to-side differences in Achilles tendon geometry and mechanical properties following achilles tendon rupture

Side-to-side differences in Achilles tendon geometry and mechanical properties following achilles tendon rupture

Effects of tear size and location on predictions of supraspinatus tear propagation

Rotator cuff tears remain a significant clinical problem with a high incidence rate and severe clinical burden. Previous computational models developed to study rotator cuff tears have not modeled tissue damage and tear propagation. The objective of this study was to predict tear propagation for various combinations of tear size and location using an experimentally validated finite element model of supraspinatus tendon. It was hypothesized that larger rotator cuff tears propagate at lower loads than smaller tears, and that posterior tears require higher loads to propagate than anterior tears. Using a previously validated computational model of supraspinatus tendon, tears of size 0.5–1.5 cm were introduced to the tendon geometry in the anterior, middle, and posterior tendon thirds. Cohesive elements were assigned subject-specific failure properties and used to model tissue damage and tear propagation. A displacement of 5 mm was applied to the medial tendon edge to induce tear propagation. Model outputs included critical load required to propagate the tear, and principal stress and maximum principal strain at the anterior and posterior tear tips. For all tear sizes, posterior tears required the highest loads to propagate (247–567 N). Anterior tears generally required the least load to propagate (171–280 N). Stress and strain were larger on the articular side (maximum 33.9% articular strain vs 27.8% bursal strain). Overall, larger tears located in the anterior supraspinatus tendon that interrupt the rotator cable are most at risk for tear propagation, and should be carefully followed by clinicians when considering treatment options.

Achilles tendon stress is more sensitive to subject-specific geometry than subject-specific material properties: A finite element analysis

This study used subject-specific measures of three-dimensional (3D) free Achilles tendon geometry in conjunction with a finite element method to investigate the effect of variation in subject-specific geometry and subject-specific material properties on tendon stress during submaximal isometric loading. Achilles tendons of eight participants (Aged 25–35years) were scanned with freehand 3D ultrasound at rest and during a 70% maximum voluntary isometric contraction. Ultrasound images were segmented, volume rendered and transformed into subject-specific 3D finite element meshes. The mean (±SD) lengths, volumes and cross-sectional areas of the tendons at rest were 62±13mm, 3617±984mm3 and 58±11mm2 respectively. The measured tendon strain at 70% MVIC was 5.9±1.3%. Subject-specific material properties were obtained using an optimisation approach that minimised the difference between measured and modelled longitudinal free tendon strain. Generic geometry was represented by the average mesh and generic material properties were taken from the literature. Local stresses were subsequently computed for combinations of subject-specific and generic geometry and material properties. For a given geometry, changing from generic to subject-specific material properties had little effect on the stress distribution in the tendon. In contrast, changing from generic to subject-specific geometry had a 26-fold greater effect on tendon stress distribution. Overall, these findings indicate that the stress distribution experienced by the living free Achilles tendon of a young and healthy population during voluntary loading are more sensitive to variation in tendon geometry than variation in tendon material properties.

Side-to-side differences in Achilles tendon geometry and mechanical properties following achilles tendon rupture.

Recovery of tendon structure has been suggested to play a role in clinical success following Achilles tendon rupture. The purpose of this study was to identify side-to-side differences in tendon geometry and mechanical properties following Achilles tendon rupture and investigate the relationship of tendon structure with clinical outcomes. Participants within 1 year post complete rupture were included. Tendon geometry and mechanical properties were quantified using B-mode ultrasound imaging and continuous shear wave elastography (cSWE). Clinical outcomes included the heel-rise test. Participant self-reported function was measured using the Achilles tendon Total Rupture Score, Foot and Ankle Outcome Score - quality of life subscale, and the Physical Activity Scale. Twenty participants [mean (SD) age: 42.7(13.6) years, 13 managed surgically] were included. Tendon thickness was greater on the ruptured side (p <0.001) [median (IQR) rupture: 1.38(1.21-1.56) cm, non-rupture: 0.49(0.40-0.52)]. Tendon length to the gastrocnemius was longer (p <0.001) on ruptured [22.8 (21.71-24.31) cm] than non-ruptured [21.66(20.74-23.62) cm] sides. Viscosity was lower on the ruptured side (p <0.001) [median (IQR) rupture: 37.7(30.6-43.3) Pa*s, non-rupture: 53.5(48.4-59.6) Pa*s]. Shear modulus was not different between sides. Tendon thickness (rho = 0.675, p = 0.002) and shear modulus (rho = -0.791, p = 0.001) related to total work on the heel-rise test. Ultrasound imaging, including cSWE, can be used to detect side-to-side differences in tendon structure in individuals with Achilles tendon rupture and tendon structure relates to clinical performance. III b.

Subject-specific finite element analysis to characterize the influence of geometry and material properties in Achilles tendon rupture

Achilles tendon injuries including rupture are one of the most frequent musculoskeletal injuries, but the mechanisms for these injuries are still not fully understood. Previous in vivo and experimental studies suggest that tendon rupture mainly occurs in the tendon mid-section and predominantly more in men than women due to reasons yet to be identified. Therefore we aimed to investigate possible mechanisms for tendon rupture using finite element (FE) analysis. Specifically, we have developed a framework for generating subject-specific FE models of human Achilles tendon. A total of ten 3D FE models of human Achilles tendon were generated. Subject-specific geometries were obtained using ultrasound images and a mesh morphing technique called Free Form Deformation. Tendon material properties were obtained by performing material optimization that compared and minimized difference in uniaxial tension experimental results with model predictions. Our results showed that both tendon geometry and material properties are highly subject-specific. This subject-specificity was also evident in our rupture predictions as the locations and loads of tendon ruptures were different in all specimens tested. A parametric study was performed to characterize the influence of geometries and material properties on tendon rupture. Our results showed that tendon rupture locations were dependent largely on geometry while rupture loads were more influenced by tendon material properties. Future work will investigate the role of microstructural properties of the tissue on tendon rupture and degeneration by using advanced material descriptions.

Changes in the flexor digitorum profundus tendon geometry in the carpal tunnel due to force production and posture of metacarpophalangeal joint of the index finger: An MRI study

BackgroundCarpal tunnel syndrome is a disorder caused by increased pressure in the carpal tunnel associated with repetitive, stereotypical finger actions. Little is known about in vivo geometrical changes in the carpal tunnel caused by motion at the finger joints and exerting a fingertip force. MethodsThe hands and forearms of five subjects were scanned using a 3.0T magnetic resonance imaging scanner. The metacarpophalangeal joint of the index finger was placed in: flexion, neutral and extension. For each joint posture subjects either produced no active force (passive condition) or exerted a flexion force to resist a load (~4.0N) at the fingertip (active condition). Changes in the radii of curvature, position and transverse plane area of the flexor digitorum profundus tendons at the carpal tunnel level were measured. ResultsThe radius of curvature of the flexor digitorum profundus tendons, at the carpal tunnel level, was significantly affected by posture of the index finger metacarpophalangeal joint (P<0.05) and the radii was significantly different between fingers (P<0.05). Actively producing force caused a significant shift (P<0.05) in the flexor digitorum profundus tendons in the ventral (palmar) direction. No significant change in the area of an ellipse containing the flexor digitorum profundus tendons was observed between conditions. InterpretationThe results show that relatively small changes in the posture and force production of a single finger can lead to significant changes in the geometry of all the flexor digitorum profundus tendons in the carpal tunnel. Additionally, voluntary force production at the fingertip increases the moment arm of the FDP tendons about the wrist joint.

Effects of plyometric training on passive stiffness of gastrocnemii muscles and Achilles tendon

Plyometric training is commonly used to improve athletic performance; however, it is unclear how each component of the muscle-tendon complex (MTC) is affected by this intervention. The effects of 14weeks of plyometric training on the passive stiffness of the gastrocnemii muscles and Achilles tendon was determined simultaneously to assess possible local adaptations of elastic properties. The passive force-length relationship of the gastrocnemii MTC and elongation of the gastrocnemii muscles were determined using ultrasonography during passive cyclic stretching in 19 subjects divided into trained (n=9) and control (n=10) groups. An upward trend in stiffness of the gastrocnemii MTC (P=0.09) and a significant increase in the intrinsic gastrocnemii muscle stiffness were found (P<0.05). In contrast, no significant change in gastrocnemii tendon stiffness, or in muscle and tendon geometry, was determined (P>0.05). Considering the lack of change in gastrocnemii muscle geometry, the change in the gastrocnemii muscle stiffness may be mainly due to a change in the intrinsic mechanical properties of the muscular tissues.

Fatigue‐related changes in fascicle–tendon geometry over repeated contractions: Difference between synergist muscles

Fatigue-induced changes in force production of synergist muscles were evaluated through observation of fascicle-tendon geometry and electromyography (EMG). Seven subjects performed 60 maximal isometric plantar flexions intermittently. No statistically significant intermuscle difference was observed in the decrease of mean EMG amplitudes or mean power frequency for the medial gastrocnemius (MG) and soleus (SOL) muscles. The tendon elongation of MG significantly decreased after the 19th contraction, and MG fascicle length increased after the 29th contraction, while SOL fascicle and tendon length did not change except for the last contraction. The declines in torques were highly correlated with the increase of MG fascicle length and decrease in tendon elongation in each subject, while no consistent relationship was found for SOL. These results suggest that changes in force-production of MG and SOL over repeated contractions differ, which is reflected in fascicle-tendon geometry.