Tendon Mechanical Properties Research Articles

Intra- and inter-rater reliability for the measurement of the cross-sectional area of ankle tendons assessed by magnetic resonance imaging.

The cross-sectional area (CSA) records make an essential measurement for determining the mechanical properties of tendons, such as stress and strength. However, there is no consensus regarding the best method to record the CSA from different tendons. To determine intra- and inter-rater reliability for CSA measures from magnetic resonance imaging (MRI) of the following tendons: tibialis anterior; tibialis posterior; fibularis longus and brevis; and Achilles. We designed an observational study with repeated measures taken from a convenience sample of 20 participants diagnosed with acute or chronic ankle sprain. Two independent raters took three separate records from the CSA of ankle tendon images of each MRI slice. The intra-class correlation coefficient (ICC) and 95% limits of agreement (LoA) defined the quality (associations) and magnitude (differences), respectively, of intra- and inter-rater reliability on the measures plotted by the Bland-Altman method. Data showed very high intra- and inter-rater correlations for measures taken from all tendons analyzed (ICC 0.952-0.999). It also revealed an excellent agreement between raters (0.12%-2.3%), with bias no higher than 2 mm2 and LoA in the range of 4.4-7.9 mm2. The differences between repeated measures recorded from the thinnest tendons (fibularis longus and brevis) revealed the lowest bias and narrowest 95% LoA. Reliability for the CSA of ankle tendons measured from MRI taken by independent rates was very high, with the smallest differences between raters observed when the thinnest tendon was analyzed.

Regenerative Rehabilitation in Injuries of Tendons

The mechanical properties of tendons are thought to be affected by different loading levels. Changes in the mechanical properties of tendons, such as stiffness, have been reported to influence the risk of tendon injuries chiefly in athletes and the elderly, thereby affecting motor function execution. Unloading resulted in reduced tendons stiffness, and resistance exercise exercise counteracts this. Transforming growth factor-1 is a potent inducer of type I collagen and mechanosensitive genes encoding tenogenic differentiation markers expression which play critical roles in tendon tissue formation, tendon healing and their adaptation during exercise. In recent years, our understanding of the molecular biology of tendons growth and repair has expanded. It is probable that the next advance in the treatment of tendon injuries will result from the application of this basic science knowledge and the clinical solution will encompass not only the the best postoperative rehabilitation protocols, but also the optimal biological modulation of the healing process.

Limited Scar Resection for Chronic Achilles Tendon Repair: Use of a Rat Model

Background: Achilles tendon rupture diagnosis is frequently missed, leading to the development of a chronic rupture that requires surgical intervention to remove scar tissue and return the elongated Achilles tendon to appropriate functional length. The limited scar resection (LSR) intervention strategy may provide an advantage over other techniques, as it is less invasive and nondestructive to other tissues, although there is little evidence comparing outcomes between intervention strategies. Hypothesis: The LSR technique would be a viable treatment option for chronic Achilles tendon ruptures and would perform comparably with a more clinically accepted procedure, the gastrocnemius fascial turndown (GFT), in postintervention functional outcome measures and tendon mechanical and histological properties. Study Design: Controlled laboratory study. Methods: Chronic Achilles tendon ruptures were induced in the right hindlimb of Sprague-Dawley rats by Achilles tendon transection without repair, immobilization in dorsiflexion, and 5 weeks of cage activity. Animals were randomly divided between the intervention strategy groups (LSR and GFT), received 1 week of immobilization in plantarflexion, and were sacrificed at 3 or 6 weeks postintervention. In vivo functional outcome measures (gait kinetics, passive joint function, tendon vascular perfusion) were quantified during healing, and tendon mechanical and histological properties were assessed postsacrifice. Results: When compared with the GFT, the LSR technique elicited a faster return to baseline in gait kinetics, although there were few differences between groups or with healing time in other functional outcome measures (passive joint function and vascular perfusion). Quasi-static mechanical properties were improved with healing in both surgical intervention groups, although only the LSR group showed an improvement in fatigue properties between 3 and 6 weeks postintervention. Histological properties were similar between intervention strategies, except for decreased cellularity in the LSR group at 6 weeks postintervention. Conclusion: The LSR technique is a viable surgical intervention strategy for a chronic Achilles tendon rupture in a rodent model, and it performs similarly, if not better, when directly compared with a more clinically accepted surgery, the GFT. Clinical Relevance: This study supports the increased clinical use of the LSR technique for treating chronic Achilles tendon rupture cases.

Prevention of strain-induced impairments of patellar tendon micromorphology in adolescent athletes.

High-level patellar tendon strain may cause impairments of the tendon's micromorphological integrity in growing athletes and increase the risk for tendinopathy. This study investigated if an evidence-based tendon exercise intervention prevents high-level patellar tendon strain, impairments of micromorphology and pain in adolescent basketball players (male, 13-15years). At three time points over a season (M1-3), tendon mechanical properties were measured using ultrasound and dynamometry, proximal tendon micromorphology with a spatial frequency analysis and pain and disability using VISA-P scores. The control group (CON, n=19) followed the usual strength training plan, including sprint and change-of-direction drills. In the intervention group (INT, n=14), three sessions per week with functional exercises were integrated into the training, providing repetitive high-magnitude tendon loading for at least 3s per repetition. The frequency of high-level strain (ie, ≥9%) continuously decreased in INT, while tending to increase in CON since tendon force increased in both (p<0.001), yet tendon stiffness only in INT (p=0.004). In CON, tendon strain was inversely associated with tendon peak spatial frequency at all time points (p<0.05), indicating impairments of tendon micromorphological integrity with higher strain, but not at M2 and M3 in INT. Descriptively, the fraction of asymptomatic athletes at baseline was similar in both groups (~70%) and increased to 100% in M3 in INT, while remaining unchanged in CON. We suggest that functional high-load tendon exercises could reduce the prevalence of high-level patellar tendon strain and associated impairments of its micromorphology in adolescent athletes, providing new opportunities for tendinopathy prevention.

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.

The Impact of Hypercholesterolemia on Tendon Injury Repair

Background Hypercholesterolemia is a condition characterized by high blood cholesterol levels and is associated with tendon xanthomas (cholesterol deposits found on superficial tendons). Lipid accumulation in the tendon's extracellular spaces1 may disrupt the parallel organization of collagen substructures within the tendon, and negatively affect its mechano-sensing and mechanical properties, which may lead to injury. We hypothesized that tendon strength and metabolism would be inferior in a high cholesterol environment and attenuate the tendon's ability to repair after injury. Methods 50 Sprague-Dawley (SD, control) and 50 apolipoprotein E knock-out rats (ApoE, Envigo, IL, USA) rats bred in-house were subject to a unilateral patellar tendon (PT) injury at 12 weeks of age; the uninjured limb served as a control. Animals were euthanased at 3, 14 or 42 days post-injury, time-points chosen to represent tendon inflammatory, reparative and remodelling repair phases, respectively. Animals were randomly assigned for investigating gene expression (SD/ApoE per timepoint n=4/4), tissue histology (n=6/6), biomechanical testing (n=10/10; 14 and 42 days only). Equal male/female ratios were used where possible (total SD M23/F27, ApoE M23/F26). Results ApoE total cholesterol was over double that of SD rats (mean 2.12 vs 0.99 mg/ml, p<0.001). Despite this, there was little histological evidence of lipid content (Oil Red-O staining) in tendons of either group, and no apparent differences in tendon mechanical or material properties (Fig. 1). However, there were differences in gene expression (Fig. 2). ApoE rats demonstrated significantly greater COX2 expression than SD; other inflammatory markers (TGFβ, IL-1, IL-6) did not differ between groups. COL1A1, SCX, LOXα were significantly upregulated 14 days post injury in SD compared to ApoE. A greater COL3A1 response was also observed in ApoE compared to SD rats. Discussion We found differences in injury repair at the cellular level, using an ApoE high cholesterol model. There was little evidence of lipid accumulation at the tissue level, therefore the PT may have been a poor choice for an injury study in this instance and it is not surprising that biomechanical differences were not found. Moreover, ApoE rats were recently found to demonstrate only modest early atherosclerotic characteristics2, thus the young age of our cohort may be a primary factor in the lack of physical evidence of lipid accumulation. Nonetheless, our results indicate that even with a mild phenotype, high cholesterol significantly modulates tendon inflammatory and healing cellular activity, as indicated by altered mRNA levels, which may contribute to the known consequences of tendon cholesterol on tendons in humans. References 1Grewal et al. 2014. Accumulation of oxidized LDL in the tendon tissues of C57BL/6 or apolipoprotein E knock-out mice that consume a high fat diet: potential impact on tendon health. PLoS One 9(12): e114214. 2Rune et al., 2018. Long-term Western diet fed apolipoprotein E-deficient rats exhibit only modest early atherosclerotic characteristics. Sci Rep 8(1): 5416.

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

Neonatal Spinal Cord Transection Decreases Hindlimb Weight-Bearing and Affects Formation of Achilles and Tail Tendons.

Mechanical loading may be required for proper tendon formation. However, it is not well understood how tendon formation is impacted by the development of weight-bearing locomotor activity in the neonate. This study assessed tendon mechanical properties, and concomitant changes in weight-bearing locomotion, in neonatal rats subjected to a low thoracic spinal cord transection or a sham surgery at postnatal day (P)1. On P10, spontaneous locomotion was evaluated in spinal cord transected and sham controls to determine impacts on weight-bearing hindlimb movement. The mechanical properties of P10 Achilles tendons (ATs), as representative energy-storing, weight-bearing tendons, and tail tendons (TTs), as representative positional, non-weight-bearing tendons were evaluated. Non- and partial weight-bearing hindlimb activity decreased in spinal cord transected rats compared to sham controls. No spinal cord transected rats showed full weight-bearing locomotion. ATs from spinal cord transected rats had increased elastic modulus, while cross-sectional area trended lower compared to sham rats. TTs from spinal cord transected rats had higher stiffness and cross-sectional area. Collagen structure of ATs and TTs did not appear impacted by surgery condition, and no significant differences were detected in the collagen crimp pattern. Our findings suggest that mechanical loading from weight-bearing locomotor activity during development regulates neonatal AT lateral expansion and maintains tendon compliance, and that TTs may be differentially regulated. The onset and gradual increase of weight-bearing movement in the neonate may provide the mechanical loading needed to direct functional postnatal tendon formation.

Comparison between dry needling and focused ultrasound on the mechanical properties of the rat Achilles tendon: A pilot study

In the U.S., approximately 14 million tendon and ligament injuries are reported each year. Dry needling (DN) is a conservative treatment introduced to alleviate pain and restore function; however, it is invasive and has mixed success. Focused ultrasound (fUS) is a non-invasive technology that directs ultrasound energy into a well-defined focal volume. fUS induces thermal and/or mechanical bioeffects which can be controlled by the choice of ultrasound parameters. fUS could be an alternative to DN for treatment of tendon injuries, but the bioeffects must be established. Thus, the purpose of this pilot study was to compare the effect of DN and fUS on the mechanical properties and cell morphology of 30 ex vivo rat Achilles tendons. Tendons were randomly assigned to sham, DN, or fUS, with 10 tendons per group. Within each group, 5 tendons were evaluated mechanically, and 5 tendons were analyzed histologically. Elastic modulus in the DN (74.05 ± 15.0 MPa) group was significantly lower than sham (149.84 ± 59.1 MPa; p = 0.0094) and fUS (128.84 ± 28.3 MPa; p = 0.0453) groups. Stiffness in DN (329.05 ± 236.8 N/mm; p = 0.0034) and fUS (315.26 ± 68.9 N/mm; p = 0.0027) groups were significantly lower than sham (786.10 ± 238.7 N/mm) group. Histologically, localized necrosis was observed in 3 out of 5 tendons exposed to fUS, with surrounding tissue unharmed; no evidence of cellular injury was observed in DN or sham groups. These results suggest that fUS preserves the mechanical properties of tendon better than DN. Further studies are needed to evaluate fUS as an alternative, noninvasive treatment modality for tendon injuries.

Effect of a 10-Week Stretching Program of the Triceps Surae Muscle Architecture and Tendon Mechanical Properties

The present study aimed to test if a long-term passive stretching training causes adaptations of the medial gastrocnemius architecture and the Achilles tendon (AT) tangent modulus. A total of 20 males took part in the study. The stretching group (n = 12), performed stretching exercises for the plantar flexors for 10 weeks, 4–5 times a week, which comprised two static positions sustained twice each during 30 s. For the stretching group, maximum dorsiflexion angle, peak passive torque, and muscle–tendon unit maximum length significantly increased after training. No other differences were found related to muscle architecture and AT tangent modulus. Joint amplitude gain after a long-term stretching of the triceps surae was not accompanied by structural or mechanical changes of the medial gastrocnemius and AT tendon, and seems to reflect an increasing stretch tolerance level.

Differences in cellular and microstructural properties of the semitendinosus muscle tendon between young and adult patients

BackgroundPoor outcomes associated with anterior cruciate ligament reconstruction in paediatric patients are a major concern. The tendon structure and its cellular characteristics are key factors that affect the mechanical properties of tendons. This study aimed to evaluate the effects of growth on the cellular and microstructural properties of the tendon of the semitendinosus muscle in humans. MethodsSemitendinosus muscle tendon samples from 76 patients who underwent ligament reconstruction were examined and divided into three groups: immature (10.8 ± 2.7 years old), young (16.5 ± 1.8 years old), and adult (35.2 ± 8.6 years old), based on age and the state of the epiphyseal plate in the distal femur. The number of tendon cells per unit area was assessed, and the major-to-minor-length ratio of the tendon cell nuclei was calculated to evaluate the shape of the nuclei using haematoxylin and eosin staining. The collagen fibril diameter and distribution were determined using electron microscopy. ResultsThe major-to-minor-length ratio of the tendon cell nuclei significantly increased with age (p-value; immature vs. young: 0.018, young vs adult: 0.001, immature vs adult: 0.001). The shape of the tendon cell nuclei was rounder in the immature group and more elongated in the adult group. A significant decrease in the number of tendon cells was observed with age (immature: 565 ± 134/mm2, young: 356 ± 105/mm2, adult: 272 ± 81/mm2; p-value: immature vs young: 0.001, young vs adult: 0.012, immature vs adult: 0.001). The mean fibril diameter in the immature group was significantly smaller (p-value: immature vs young: 0.018, young vs adult: 0.001, immature vs adult: 0.001). The distribution of the collagen fibrils changed from right skewed in the immature group to flat in the adult group. ConclusionsThe characteristics of the tendon cells and the microstructure of collagen in muscle tendons significantly changed with age.

A Functional High-Load Exercise Intervention for the Patellar Tendon Reduces Tendon Pain Prevalence During a Competitive Season in Adolescent Handball Players.

Imbalances of muscle strength and tendon stiffness may increase the risk for patellar tendinopathy in growing athletes. The present study investigated if a functional high-load exercise intervention, designed to facilitate tendon adaptation and reduce muscle-tendon imbalances, may prevent patellar tendon pain in adolescent male handball players (12–14 years). Tendon pain prevalence (using VISA-P scores), knee extensor strength, vastus lateralis (VL) architecture and patellar tendon mechanical properties were measured at four measurement time points (M1–M4) over a season. The control group (CON; n = 18; age 13.1 ± 0.7 yrs, height 170 ± 8 cm, mass 58 ± 10 kg) followed the usual strength training plan, including muscular endurance and explosive strength components. In the experimental group (EXP; n = 16; 13.1 ± 0.6 yrs, 169 ± 11 cm, 58 ± 16 kg), two sessions per week with functional high-load exercises for the patellar tendon were integrated in the strength training schedule, aiming to provide repetitive high-intensity loading of at least 3 s loading duration per repetition. While in the control group 30% of the athletes reported a clinically significant aggravation of symptoms, all players in the experimental group remained or became pain-free at M2 until the end of the season. There was a similar increase of strength (normalized to body mass; CON: 3.1%, d = 0.22; EXP: 6.8%, d = 0.47; p = 0.04) and VL thickness (CON: 4.8%, d = 0.28; EXP: 5.7%, d = 0.32; p < 0.001) in both groups, but no significant changes of tendon stiffness or maximum tendon strain. Further, both groups demonstrated similar fluctuations of tendon strain over time. We conclude that functional high-load exercises can reduce the prevalence of patellar tendon pain in adolescent athletes even without a reduction of tendon strain.

Correlation between Patellar Tendon Mechanical Properties and Oxygenation Detection by Near Infrared Spectroscopy in Males

Correlation between Patellar Tendon Mechanical Properties and Oxygenation Detection by Near Infrared Spectroscopy in Males

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.

Mechanical properties of the different rotator cuff tendons in the rat are similarly and adversely affected by age

Rotator cuff tendon tears and tendinopathies are common injuries affecting a large portion of the population and can result in pain and joint dysfunction. Incidence of rotator cuff tears significantly increases with advancing age, and up to 90% of these tears involve the supraspinatus. Previous literature has shown that aging can lead to inferior mechanics, altered composition, and changes in structural properties of the supraspinatus. However, there is little known about changes in supraspinatus mechanical properties in context of other rotator cuff tendons. Alterations in tendon mechanical properties may indicate damage and an increased risk of rupture, and thus, the purpose of this study was to use a rat model to define age-related alterations in rotator cuff tendon mechanics to determine why the supraspinatus is more susceptible to tears due to aging than the infraspinatus, subscapularis, and teres minor. Fatigue, viscoelastic, and quasi-static properties were evaluated in juvenile, adult, aged, and geriatric rats. Aging ubiquitously and adversely affected all rotator cuff tendons tested, particularly leading to increased stiffness, decreased stress relaxation, and decreased fatigue secant and tangent moduli in geriatric animals, suggesting a common intrinsic mechanism due to aging in all rotator cuff tendons. This study demonstrates that aging has a significant effect on rotator cuff tendon mechanical properties, though the supraspinatus was not preferentially affected. Thus, we are unable to attribute the aging-associated increase in supraspinatus tears to its mechanical response alone.

In vivo manipulation of muscle shape and tendinous stiffness affects the human ability to generate torque rapidly.

What is the central question of this study? What are the determinants of muscle belly gearing, and how does it affect the torque rise? What is the main finding and its importance? Change in muscle thickness of the gastrocnemius medialis is related to variations in belly gearing. Belly gearing has a key role in the rise of muscle torque and rate of torque development (RTD). Besides, the increase of tendinous tissue stiffness could increase the torque rise as well, and in turn, the RTD. However, changes in the tendinous tissue stiffness showed no effects on muscle fascicle behaviour, suggesting a possible uncoupling between muscle and tendon mechanical properties. During fixed-end contractions, muscles bulge in thickness and/or width to maintain a constant volume, whereas tendons lengthen over the entire contraction period. These dynamic changes play a key functional role in modulating the generated torque. However, the literature has revealed a limited understanding of in vivo dynamic muscle-tendon changes during rapid contractions. Therefore, this study aimed to investigate the determinants of belly gearing (belly velocity/fascicle velocity) and its effects on rapid torque production during in vivo fixed-end contractions. Twenty healthy males were recruited for the study. Muscle shape and tendon stiffness were manipulated by applying a transverse load (2-10kg) and an ankle rotation manoeuvre, respectively. Ultrafast-ultrasound was employed to quantify medial gastrocnemius architecture during evoked contraction and a dynamometer was used to measure the muscle torque and quantify the rate of torque development (RTD). Torque and RTD diminished by transverse load application, whereas they increased during the ankle rotation manoeuvre. Belly gearing declined with increasing transverse load but was unaffected by tendinous stiffness variations. Alterations in belly gearing were strongly related to variations in muscle thickness throughout any load applied and affected the torque rise rapidly. In contrast, changes in tendinous tissue stiffness affected the torque rise only but did not modify the muscle shape. These data may suggest that concurrent manipulation of the tendinous tissue stiffness and muscle shape does not affect the explosive rise in torque capacity, suggesting a possible uncoupling between mechanical properties of muscle and tendon.

Stiffness of the Gastrocnemius-Achilles Tendon Complex Between Amateur Basketball Players and the Non-athletic General Population.

Muscle and tendon stiffness are related to sports performance, tendinopathy, and tendon degeneration. However, the effects of habitual loading on muscle and tendon mechanical properties are unclear. Using amateur basketball players as examples, we investigated the effects of mechanical loading on the stiffness of the gastrocnemius–Achilles tendon (AT) complex in non-dominant and dominant lower limbs. Then, we evaluated the correlation between gastrocnemius and AT stiffness. Forty participants (20 amateur basketball players; 20 normal non-athletic persons) were recruited for this study. Stiffness of the gastrocnemius–AT complex was assessed using MyotonPRO at neutral position and 10° dorsiflexion of the ankle joint in participants from amateur basketball players and the non-athletic general population. Our results showed a greater stiffness of the gastrocnemius–AT complex in amateur basketball players than that in healthy non-athletic subjects at neutral position and 10° dorsiflexion of the ankle joint (P < 0.05). No significant difference in stiffness was found between the non-dominant and dominant lower limbs either in amateur basketball players or in generally healthy subjects (P > 0.05). A significant positive correlation was obtained between stiffness of the AT and medial gastrocnemius (MG) in amateur basketball players (neutral position: r = 0.726 and P = 0.001; dorsiflexion 10°: r = 0.687 and P = 0.001). The amateur basketball players exhibit significantly higher stiffness value in Achilles and gastrocnemius. This is possibly caused by repeated training effects. The symmetric stiffness of the AT and gastrocnemius exists both in amateur basketball players and generally healthy subjects. A significant correlation between the AT and the MG was found in amateur basketball players.

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.

Chronic Nicotine Exposure Minimally Affects Rat Supraspinatus Tendon Properties and Bone Microstructure.

Cigarette smoking is the largest cause of preventable deaths, and a known risk factor for musculoskeletal issues including rotator cuff tendon tears. Tendon degeneration is believed to be due in part to changes in tendon cell health and collagen structure. Several studies have demonstrated that exposure to nicotine negatively impacts tendon healing, but surprisingly, nicotine exposure was shown to increase rat supraspinatus tendon stiffness. In order to address this seeming contradiction, the objective of this study was to comprehensively investigate the effects of long-term (18weeks) exposure of nicotine on tendon-to-bone microstructural properties in a rat model. We hypothesized that long term subcutaneous nicotine delivery would lead to diminished tendon mechanical properties, decreased bone microstructure in the humeral head, and altered tendon cell morphology compared to age-matched control rats receiving saline. Results demonstrated a small decrease in tendon size and stiffness, with decreased cell density in the tendon midsubstance. However, no differences were found in the enthesis fibrocartilage or in the underlying subchondral or trabecular bone. In conclusion, our study revealed limited effects of nicotine on the homeostatic condition of the supraspinatus tendon, enthesis, and underlying bone. Future studies are needed to ascertain effects of other components of tobacco products.