Training-induced changes in peritendinous type I collagen turnover determined by microdialysis in humans

Collagen denaturation in post-run Achilles tendons and Achilles tendinopathy: In vivo mechanophysiology and magnetic resonance imaging

Achilles tendinopathy is often attributed to overuse, but its pathophysiology remains poorly understood. Disruption to the molecular structure of collagen is fundamental for the onset and progression of tendinopathy but has mostly been investigated in vitro. Here, we interrogated the in vivo molecular structure changes of collagen in rat Achilles tendons following treadmill running. Unexpectedly, the tendons' collagen molecules were not mechanically unfolded by running but denatured through proteolysis during physiological post-run remodeling. We further revealed that running induces inflammatory gene expressions in Achilles tendons and that long-term running causes prolonged, elevated collagen degradation, leading to the accumulation of denatured collagen and tendinopathy development. For applications, we demonstrated magnetic resonance imaging of collagenase-induced Achilles tendon injury in vivo using a denatured collagen targeting contrast agent. Our findings may help close the knowledge gaps in the mechanobiology and pathogenesis of Achilles tendinopathy and initiate new strategies for its imaging-based diagnosis.

Functionality and jump performance in patellar tendinopathy with the application of three different treatments

OBJECTIVES

The aim is to assess performance characteristics in jumps and functionality in participants with patellar tendinopathy and compare changes with various tendinopathy treatments in the short and medium term. As a secondary objective, the study aims to verify the relationship between changes in knee functionality assessed by the VISA-P and jump capacity in the different treatment groups.

DESIGN

A double-blinded randomized controlled trial.

METHODS

Recruitment was conducted at sport clubs, with 48 participants with patellar tendinopathy included in the study. Participants were randomized into groups: dry needling (DN), percutaneous electrolysis (PNE), and sham needling as the control group (CG), all combined with eccentric exercise (EE). Functionality and performance during jumps, including squat jump (SJ) and counter movement jump (CMJ), were assessed.

RESULTS

Significant differences were found in functionality between the pre-test and post-test evaluations, as well as between the pre-test and follow-up evaluations, in all three groups (p < 0.001). The DN group experienced an improvement in eccentric power (p = 0.021). A moderate correlation was found between the pre-test and post-test changes in functionality and SJ maximum concentric force (r = 0.63, p < 0.01, CI: 0.1; 0.8), CMJ maximum concentric force (r = 0.52, p = 0.05, CI: -0.01; 0.8), and CMJ eccentric power in the DN group (r = 0.63, p = 0.01, CI: 0.1; 0.8).

CONCLUSIONS

Eccentric exercise could be effective in improving functionality in patellar tendinopathy and DN could improve eccentric power in jumps performance. Moreover, the DN group experienced an increase in functionality that correlated with the improvements found in jump performance in eccentric power and concentric strength.

The Collagen Synthesis Response to an Acute Bout of Resistance Exercise Is Greater when Ingesting 30 g Hydrolyzed Collagen Compared with 15 g and 0 g in Resistance-Trained Young Men

BACKGROUND

Resistance exercise (RE) stimulates collagen synthesis in skeletal muscle and tendon but there is limited and equivocal evidence regarding an effect of collagen supplementation and exercise on collagen synthesis. Furthermore, it is not known if a dose-response exists regarding the effect of hydrolyzed collagen (HC) ingestion and RE on collagen synthesis.

OBJECTIVE

To determine the HC dose-response effect on collagen synthesis after high-intensity RE in resistance-trained young men.

METHODS

Using a double-blind, randomized crossover design, 10 resistance-trained males (age: 26 ± 3 y; height: 1.77 ± 0.04 m; mass: 79.7 ± 7.0 kg) ingested 0 g, 15 g, or 30 g HC with 50 mg vitamin C 1 h before performing 4 sets' barbell back squat RE at 10-repetition maximum load, after which they rested for 6 h. Blood samples were collected throughout each of the 3 interventions to analyze procollagen type Ⅰ N-terminal propeptide (PINP) and β-isomerized C-terminal telopeptide of type I collagen (β-CTX) concentration, and the concentration of 18 collagen amino acids.

RESULTS

The serum PINP concentration × time area under the curve (AUC) was greater for 30 g (267 ± 79 μg·L-1·h) than for 15 g (235 ± 70 μg·L-1·h, P = 0.013) and 0 g HC (219 ± 88 μg·L-1·h, P = 0.002) but there was no difference between 0 and 15 g HC (P = 0.225). The AUCs of glycine and proline were greater for 30 g than for 15 and 0 g HC (P < 0.05). Plasma β-CTX concentration decreased from -1 to +6 h (P < 0.05), with no differences between interventions.

CONCLUSIONS

Ingesting 30 g HC before high-intensity RE augments whole-body collagen synthesis more than 15 g and 0 g HC in resistance-trained young males.

Mechanical properties, collagen and glycosaminoglycan content of equine superficial digital flexor tendons are not affected by training

Physical activity can activate extracellular matrix (ECM) protein synthesis and influence the size and mechanical properties of tendon. In this study, we aimed to investigate whether different training histories of horses would influence the synthesis of collagen and other matrix proteins and alter the mechanical properties of tendon. Samples from superficial digital flexor tendon (SDFT) from horses that were either (a) currently race trained (n = 5), (b) previously race trained (n = 5) or (c) untrained (n = 4) were analysed for matrix protein abundance (mass spectrometry), collagen and glycosaminoglycan (GAG) content, ECM gene expression and mechanical properties. It was found that ECM synthesis by tendon fibroblasts in vitro varied depending upon the previous training history. In contrast, fascicle morphology, collagen and GAG content, mechanical properties and ECM gene expression of the tendon did not reveal any significant differences between groups. In conclusion, although we could not identify any direct impact of the physical training history on the mechanical properties or major ECM components of the tendon, it is evident that horse tendon cells are responsive to loading in vivo, and the training background may lead to a modification in the composition of newly synthesised matrix.

Novel application of in vivo microdialysis in a rat Achilles tendon acute injury model

Tendon injury and healing involve intricate changes to tissue metabolism, biology, and inflammation. Current techniques often require animal euthanasia or tissue destruction, limiting assessment of dynamic changes in tendon, including treatment response, disease development, rupture risk, and healing progression. Microdialysis, a minimally invasive technique, offers potential for longitudinal assessment, yet it has not been applied to rat tendon models. Therefore, the objective of this study is to adapt a novel application of an in vivo assay, microdialysis, using acute injury as a model for extreme disruption of the tendon homeostasis. We hypothesize that microdialysis will be able to detect measurable differences in the healing responses of acute injury with high specificity and sensitivity. Overall results suggest that microdialysis is a promising in vivo technique for longitudinal assessment for this system with strong correlations between extracellular fluid (ECF) and dialysate concentrations and reasonable recovery rates considering the limitations of this model. Strong positive correlations were found between dialysate and extracellular fluid (ECF) concentration for each target molecule of interest including metabolites, inflammatory mediators, and collagen synthesis and degradation byproducts. These results suggest that microdialysis is capable of detecting changes in tendon healing following acute tendon injury with high specificity and sensitivity. In summary, this is the first study to apply microdialysis to a rat tendon model and assess its efficacy as a direct measurement of tendon metabolism, biology, and inflammation.NEW & NOTEWORTHY This study adapts a novel application of microdialysis to rat tendon models, offering a minimally invasive avenue for longitudinal tendon assessment. Successfully detecting changes in tendon healing after acute injury, it showcases strong correlations between extracellular fluid and dialysate concentrations. The results highlight the potential of microdialysis as a direct measure of tendon metabolism, biology, and inflammation, bypassing the need for animal euthanasia and tissue destruction.

Whole Genome Expression Profiling of Semitendinosus Tendons from Children with Diplegic and Tetraplegic Cerebral Palsy

Cerebral palsy (CP) is the most common movement disorder in children, with a prevalence ranging from 1.5 to 4 per 1000 live births. CP is caused by a non-progressive lesion of the developing brain, leading to progressive alterations of the musculoskeletal system, including spasticity, often leading to the development of fixed contractures, necessitating tendon lengthening surgery. Total RNA-sequencing analysis was performed on semitendinosus tendons from diplegic and tetraplegic CP patients subjected to tendon lengthening surgery compared to control patients undergoing anterior cruciate ligament reconstructive surgery. Tetraplegic CP patients showed increased expression of genes implicated in collagen synthesis and extracellular matrix (ECM) turnover, while only minor changes were observed in diplegic CP patients. In addition, tendons from tetraplegic CP patients showed an enrichment for upregulated genes involved in vesicle-mediated transport and downregulated genes involved in cytokine and apoptotic signaling. Overall, our results indicate increased ECM turnover with increased net synthesis of collagen in tetraplegic CP patients without activation of inflammatory and apoptotic pathways, similar to observations in athletes where ECM remodeling results in increased tendon stiffness and tensile strength. Nevertheless, the resulting increased tendon stiffness is an important issue in clinical practice, where surgery is often required to restore joint mobility.

Biomechanical and histological changes secondary to aging in the human rotator cuff: A preliminary analysis

The high failure rate of rotator cuff repair surgeries is positively correlated with age, yet the biomechanical changes to the tendons of the rotator cuff with age have not been described. As such, we sought to benchmark and characterize the biomechanical and histopathological properties with the accompanying gene expression of human rotator cuff tendons as a function of age and histopathological degeneration. All four rotator cuff tendons from fresh human cadaver shoulders underwent biomechanical, histopathological, and gene expression analyses. Following cadaver availability, samples were grouped into Younger (i.e., less than 36 years of age, n = 2 donors) and Aged (i.e., greater than 55 years of age, n = 3 donors) as a means of characterizing and quantifying the age-related changes exhibited by the tendons. Biomechanical testing and subsequent computational modeling techniques revealed both differences in properties between tendons and greater Young's moduli in the Younger tendons (supraspinatus 3.06x, infraspinatus 1.76x, subscapularis 1.25x, and teres minor 1.32x). Histopathological scoring using the semi-quantitative Bonar scoring scheme revealed a positive correlation with age across all tendons (r = 0.508, p < 0.001). These data contextualize the biomechanical and histopathological changes to tendons that occurs naturally with aging, highlighting the innate differences in biomechanical properties of all four rotator cuff tendons, as well as the difference in their degenerative trajectories. Additionally, the histopathological scoring revealed moderate signs of degeneration within the Younger supraspinatus tendons, suggesting tissue quality may decrease in this specific tendon in patients less than 40 years old, before clinical symptoms or tears.

Correlations between Achilles tendon material and structural properties and quantitative magnetic resonance imagining in different athletic populations

Achilles tendon stiffness (kAT) and Young's modulus (yAT) are important determinants of tendon function. However, their evaluation requires sophisticated equipment and time-consuming procedures. The goal of this study was twofold: to compare kAT and yAT between populations using the classical approach proposed in the literature (a combination of ultrasound and force data) and the MRI technique to understand the MRI's capability in determining differences in kAT and yAT. Furthermore, we investigated potential correlations between short and long T2* relaxation time, kAT and yAT to determine whether T2* relaxation time may be associated with material or structural properties. Twelve endurance and power athlete, and twelve healthy controls were recruited. AT T2* short and long components were measured using standard gradient echo MRI at rest, while kAT and yAT were evaluated using the classical method (combination of ultrasound and dynamometric measurements). Power athletes had the highest kAT (3064 ± 260, 2714 ± 260 and 2238 ± 189 N/mm for power athletes, endurance athletes and healthy control, respectively) and yAT (2.39 ± 0.28, 1.64 ± 0.22 and 1.97 ± 0.32 GPa for power athletes, endurance athletes and healthy control, respectively) and the lowest T2* short component (0.58 ± 0.07, 0.77 ± 0.06 and 0.74 ± 0.08 ms for power athletes, endurance athletes and healthy control, respectively). Endurance athletes had the highest T2* long component value. No correlations were reported between T2* long component, kAT or yAT in the investigated populations, whereas the T2* short component was negatively correlated with yAT. These results suggest that T2* short component could be used to investigate the differences in AT material properties in different populations.

Exercise builds the scaffold of life: muscle extracellular matrix biomarker responses to physical activity, inactivity, and aging

Skeletal muscle extracellular matrix (ECM) is critical for muscle force production and the regulation of important physiological processes during growth, regeneration, and remodelling. ECM remodelling is a tightly orchestrated process, sensitive to multi-directional tensile and compressive stresses and damaging stimuli, and its assessment can convey important information on rehabilitation effectiveness, injury, and disease. Despite its profound importance, ECM biomarkers are underused in studies examining the effects of exercise, disuse, or aging on muscle function, growth, and structure. This review examines patterns of short- and long-term changes in the synthesis and concentrations of ECM markers in biofluids and tissues, which may be useful for describing the time course of ECM remodelling following physical activity and disuse. Forces imposed on the ECM during physical activity critically affect cell signalling while disuse causes non-optimal adaptations, including connective tissue proliferation. The goal of this review is to inform researchers, and rehabilitation, medical, and exercise practitioners better about the role of ECM biomarkers in research and clinical environments to accelerate the development of targeted physical activity treatments, improve ECM status assessment, and enhance function in aging, injury, and disease.

Outcomes of early versus late functional weight-bearing after the acute Achilles tendon rupture repair with minimally invasive surgery: a randomized controlled trial

INTRODUCTION

Optimal postoperative rehabilitation regimen for acute Achilles tendon rupture (AATR) remains unclear. It is important to evaluate whether early functional weight-bearing rehabilitation program after minimally invasive repair results in an earlier return to pre-injury activity but increases the risk of re-rupture.

MATERIALS AND METHODS

This was a prospective randomized controlled trial involving 68 AATR patients undergoing minimally invasive surgery. 34 patients were enrolled in early weight‑bearing mobilization accelerated rehabilitation group (AR group); 34 patients were enrolled in the traditional rehabilitation (TR) group. Outcomes measures included American Orthopaedic Foot and Ankle Society Score (AOFAS) score and Achilles Tendon Total Rupture Score (ATRS) score before surgery and 3, 6, and 12 months after surgery, incidence rate of Achilles tendon re-rupture and total complications, length of hospital stay, time return to work and sports.

RESULTS

There was no significant difference in preoperative basic data between the two groups. However, AOFAS score and ATRS score were better in AR group than TR group at 3 months postoperatively (92.4 ± 3.5 vs 88.3 ± 4.5, P < 0.01; 91.1 ± 4.4 vs 88.9 ± 3.4, P = 0.03, respectively), the mean length of hospital stay (4.7 ± 1.5 vs 7.6 ± 2.0 days, P < 0.01) and time return to work (4.5 ± 1.0 vs 7.5 ± 1.6 weeks, P < 0.01) were shorter in AR group than in TR group. No statistical significance was calculated in patient-reported outcomes during the rest of the follow-up time and complications.

CONCLUSION

Early accelerated rehabilitation with weight-bearing in patients with AATR after minimally invasive surgery results in better early functional outcomes and shows similar security and feasibility.

REGISTRATION NO

ChiCTR2100043398.

Collagen supplementation augments changes in patellar tendon properties in female soccer players

We investigated the effect of collagen hydrolysate supplementation on changes in patellar tendon (PT) properties after 10 weeks' training in female soccer players from a Football Association Women's Super League Under 21 s squad. We pair-matched n = 17 players (age: 17 ± 0.9 years; height: 1.66 ± 0.06 m; mass: 58.8 ± 8.1 kg) for baseline knee extension (KE) maximum isometric voluntary contraction (MIVC) torque, age, height, and body mass, and randomly assigned them to collagen (COL) or placebo (PLA) groups (COL n = 8, PLA n = 9). Participants consumed 30 g collagen hydrolysate supplementation or energy-matched PLA (36.5 g maltodextrin, 8.4 g fructose) and plus both groups consumed 500 mg vitamin C, after each training session, which comprised bodyweight strength-, plyometric- and/or pitch-based exercise 3 days/week for 10 weeks in-season. We assessed KE MIVC torque, vastus lateralis muscle thickness and PT properties using isokinetic dynamometry and ultrasonography before and after 10 weeks' soccer training. KE MIVC torque, muscle thickness and tendon cross-sectional area did not change after training in either group. However, COL increased PT stiffness [COL, +18.0 ± 12.2% (d = 1.11) vs. PLA, +5.1 ± 10.4% (d = 0.23), p = 0.049] and Young's modulus [COL, +17.3 ± 11.9% (d = 1.21) vs. PLA, +4.8 ± 10.3% (d = 0.23), p = 0.035] more than PLA. Thus, 10 weeks' in-season soccer training with COL increased PT mechanical and material properties more than soccer training alone in high-level female soccer players. Future studies should investigate if collagen hydrolysate supplementation can improve specific aspects of female soccer performance requiring rapid transference of force, and if it can help mitigate injury risk in this under-researched population.

Variations in the Thickness of the Plantar Fascia After Training Based in Training Race. A Pilot Study

Plantar fascia (PF) is a connective tissue made up of mostly type 1 collagen that is subjected to constant loads. This study evaluated the effect of continuous running on tissue stress in the PF by measuring changes in the thickness of the PF using ultrasound scans. It was a cross-sectional study involving 24 runners from the University of Valencia, recruited as volunteers between December 2018 and February 2019. A variety of data was recorded: (age, body mass index, type of footwear, number of workouts per week, KM run per week, sports injuries in the last year, pre and postrace ultrasound PF measurements). There were significant differences in the 3 postrace measurements of the left foot (<0.001). PF thicknesses were measured before and after running, with a minimal average difference of 0.4 mm in the medial and central fascicles, and 0.3 mm in the lateral fascicle. We observed PF thicknesses above 4mm in asymptomatic patients with no signs of vascularisation, proving that increased PF thickness is not the only criterion for diagnosis of plantar fasciitis.

Metabolic and molecular responses of human patellar tendon to concentric- and eccentric-type exercise in youth and older age

Exercise training can induce adaptive changes to tendon tissue both structurally and mechanically; however, the underlying compositional changes that contribute to these alterations remain uncertain in humans, particularly in the context of the ageing tendon. The aims of the present study were to determine the molecular changes with ageing in patellar tendons in humans, as well as the responses to exercise and exercise type (eccentric (ECC) and concentric (CON)) in young and old patellar tendon. Healthy younger males (age 23.5 ± 6.1 years; n = 27) and older males (age 68.5 ± 1.9 years; n = 27) undertook 8 weeks of CON or ECC training (3 times per week; at 60% of 1 repetition maximum (1RM)) or no training. Subjects consumed D₂O throughout the protocol and tendon biopsies were collected after 4 and 8 weeks for measurement of fractional synthetic rates (FSR) of tendon protein synthesis and gene expression. There were increases in tendon protein synthesis following 4 weeks of CON and ECC training (P < 0.01; main effect by ANOVA), with no differences observed between young and old males, or training type. At the transcriptional level however, ECC in young adults generally induced greater responses of collagen and extracellular matrix-related genes than CON, while older individuals had reduced gene expression responses to training. Different training types did not appear to induce differential tendon responses in terms of protein synthesis, and while tendons from older adults exhibited different transcriptional responses to younger individuals, protein turnover changes with training were similar for both age groups.

The mechanosensitive ion channel PIEZO1 is expressed in tendons and regulates physical performance

How mechanical stress affects physical performance via tendons is not fully understood. Piezo1 is a mechanosensitive ion channel, and E756del PIEZO1 was recently found as a gain-of-function variant that is common in individuals of African descent. We generated tendon-specific knock-in mice using R2482H Piezo1, a mouse gain-of-function variant, and found that they had higher jumping abilities and faster running speeds than wild-type or muscle-specific knock-in mice. These phenotypes were associated with enhanced tendon anabolism via an increase in tendon-specific transcription factors, Mohawk and Scleraxis, but there was no evidence of changes in muscle. Biomechanical analysis showed that the tendons of R2482H Piezo1 mice were more compliant and stored more elastic energy, consistent with the enhancement of jumping ability. These phenotypes were replicated in mice with tendon-specific R2482H Piezo1 replacement after tendon maturation, indicating that PIEZO1 could be a target for promoting physical performance by enhancing function in mature tendon. The frequency of E756del PIEZO1 was higher in sprinters than in population-matched nonathletic controls in a small Jamaican cohort, suggesting a similar function in humans. Together, this human and mouse genetic and physiological evidence revealed a critical function of tendons in physical performance, which is tightly and robustly regulated by PIEZO1 in tenocytes.

Collagen and Vitamin C Supplementation Increases Lower Limb Rate of Force Development

BACKGROUND

Exercise and vitamin C-enriched collagen supplementation increase collagen synthesis, potentially increasing matrix density, stiffness, and force transfer.

PURPOSE

To determine whether vitamin C-enriched collagen (hydrolyzed collagen [HC] + C) supplementation improves rate of force development (RFD) alongside a strength training program.

METHODS

Using a double-blinded parallel design, over 3 weeks, healthy male athletes (n = 50, 18-25 years) were randomly assigned to the intervention (HC + C; 20 g HC + 50 mg vitamin C) or placebo (20 g maltodextrin). Supplements were ingested daily 60 min prior to training. Athletes completed the same targeted maximal muscle power training program. Maximal isometric squats, countermovement jumps, and squat jumps were performed on a force plate at the same time each testing day (baseline, Tests 1, 2, and 3) to measure RFD and maximal force development. Mixed-model analysis of variance compared performance variables across the study timeline, whereas t tests were used to compare the change between baseline and Test 3.

RESULTS

Over 3 weeks, maximal RFD in the HC + C group returned to baseline, whereas the placebo group remained depressed (p = .18). While both groups showed a decrease in RFD through Test 2, only the treatment group recovered RFD to baseline by Test 3 (p = .036). In the HC + C group, change in countermovement jumps eccentric deceleration impulse (p = .008) and eccentric deceleration RFD (p = .04) was improved. A strong trend was observed for lower limb stiffness assessed in the countermovement jumps (p = .08). No difference was observed in maximal force or squat jump parameters.

CONCLUSION

The HC + C supplementation improved RFD in the squat and countermovement jump alongside training.

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.

Habitual side-specific loading leads to structural, mechanical and compositional changes in the patellar tendon of young and senior life-long male athletes

Effects of life-long physical activity on tendon function have been investigated in cross-sectional studies, but these are at risk of "survivorship" bias. Here, we investigate if life-long side-specific loading is associated with greater cross-sectional area (CSA), mechanical properties, cell density (DNA content) and collagen cross-link composition of the male human patellar tendon (PT), in vivo. Nine seniors and six young male life-long elite badminton players and fencers were included. CSA of the PT obtained by 3-tesla MRI, and ultrasonography-based bilateral PT mechanics were assessed. Collagen fibril characteristics, enzymatic cross-links, non-enzymatic glycation (autofluorescence), collagen and DNA content were measured biochemically in PT biopsies. The elite athletes had a ≥15% side-to-side difference in maximal knee extensor strength, reflecting chronic unilateral sport-specific loading patterns. The PT CSA was greater on the lead extremity compared with the non-lead extremity (17 %, p=0.0001). Furthermore, greater tendon stiffness (18 %, p=0.0404) together with lower tendon stress (22 %, p=0.0005) and tendon strain (18 %, p=0.0433) were observed on the lead extremity. No effects were demonstrated from side-to-side for glycation, enzymatic cross-link, collagen, and DNA content (50%, p=0.1160). Moreover, tendon fibril density was 87±28 fibrils/μm² on the lead extremity and 68±26 fibrils/μm² on the non-lead extremity (28%, p=0.0544). Tendon fibril diameter was 86±14 nm on the lead extremity and 94±14 nm on the non-lead extremity (-9%, p=0.1076). These novel data suggest that life-long side-specific loading in males yields greater patellar tendon size and stiffness possibly with concomitant greater fibril density but without changes of collagen cross-link composition.

Hydrolyzed Collagen Supplementation on Lower Body Stiffness in Recreational Triathletes

Background: Myotendinous stiffness is related to the collagen content of the muscle and tendon, and can be estimated during running by changes in vertical stiffness (kvert) and the resulting modifications of the spatiotemporal parameters (on-off ground asymmetry and landing-takeoff asymmetry). Supplementation with amino acids found in collagen, such as proline, glycine, and hydroxyl proline, combined with ascorbic acid, improve collagen synthesis and potentially result in improved mechanical strength and stiffness. Objectives: To determine if hydrolyzed collagen (HC) supplementation increases kvert and improves the spatiotemporal parameters during running in recreational triathletes. Methods: Nine active males (weight; 68.4 ± 5.7 kg, height; 171.8 ± 5.4 cm, age; 32.5 ± 4.1 years; Vo2max; 53.15 ± 2.19 mL/kg/min) were randomly distributed into a collagen group (CollG, n = 5) and a control group (CG, n = 4). Participants were supplemented for 4 weeks with 15g HC (CollG) or 15g placebo (CG; maltodextrin), 3 times per week. One hour after supplementation, the participants of both groups were asked to perform four repetitions of short sprints to further stimulate collagen synthesis. The ground reaction forces were recorded during running at 4.44 m s-1, 5.55 m.s-1, and 6.66 m.s-1 for assessment of kvert and the spatiotemporal step parameters. Results: Both groups increased kvert with speed (4.44 - 6.66 m s-1) from 24.8 ± 2.7 to 53.7 ± 16.5 N/m and from 25.1 to 49.8 N/m in the CollG and CG, respectively (P < 0.0001); however, there were no differences between groups before and after the supplementation period. As a consequence, the spatiotemporal parameters of running were also similar between groups. Conclusions: Four weeks of HC supplementation does not improve the bouncing mechanism of running in recreational triathletes.

Molecular Basis for Mechanical Properties of ECMs: Proposed Role of Fibrillar Collagen and Proteoglycans in Tissue Biomechanics

Collagen and proteoglycans work in unison in the ECM to bear loads, store elastic energy and then dissipate excess energy to avoid tissue fatigue and premature mechanical failure. While collagen fibers store elastic energy by stretching the flexible regions in the triple helix, they do so by lowering their free energy through a reduction in the entropy and a decrease in charge-charge repulsion. Entropic increases occur when the load is released that drive the reversibility of the process and transmission of excess energy. Energy is dissipated by sliding of collagen fibrils by each other with the aid of decorin molecules that reside on the d and e bands of the native D repeat pattern. Fluid flow from the hydration layer associated with the decorin and collagen fibrils hydraulically dissipates energy during sliding. The deformation is reversed by osmotic forces that cause fluid to reform a hydration shell around the collagen fibrils when the loads are removed. In this paper a model is presented describing the organization of collagen fibers in the skin and cell-collagen mechanical relationships that exist based on non-invasive measurements made using vibrational optical coherence tomography. It is proposed that under external stress, collagen fibers form a tensional network in the plane of the skin. Collagen fiber tension along with forces generated by fibroblasts exerted on collagen fibers lead to an elastic modulus that is almost uniform throughout the plane of the skin. Tensile forces acting on cells and tissues may provide a baseline for stimulation of normal mechanotransduction. We hypothesize that during aging, changes in cellular metabolism, cell-collagen interactions and light and UV light exposure cause down regulation of mechanotransduction and tissue metabolism leading to tissue atrophy.

Regulation of tendon and ligament differentiation

Tendons transmit power from muscles to bones, and ligaments maintain the stability of joints, thus producing smooth and flexible movements of articular joints. However, tendons have poor self-healing ability upon damage due to injuries, diseases, or aging. To maintain homeostasis or promote regeneration of the tendon/ligament, it is critical to understand the mechanism responsible for the coordination of tendon/ligament-specific gene expression and subsequent cell differentiation. In this review, we have discussed the core molecular mechanisms involved in the development and homeostasis of tendons and ligaments, with particular focus on transcription factors, signaling, and mechanical stress.

Tendon Extracellular Matrix Assembly, Maintenance and Dysregulation Throughout Life

In his Lissner Award medal lecture in 2000, Stephen Cowin asked the question: "How is a tissue built?" It is not a new question, but it remains as relevant today as it did when it was asked 20 years ago. In fact, research on the organization and development of tissue structure has been a primary focus of tendon and ligament research for over two centuries. The tendon extracellular matrix (ECM) is critical to overall tissue function; it gives the tissue its unique mechanical properties, exhibiting complex non-linear responses, viscoelasticity and flow mechanisms, excellent energy storage and fatigue resistance. This matrix also creates a unique microenvironment for resident cells, allowing cells to maintain their phenotype and translate mechanical and chemical signals into biological responses. Importantly, this architecture is constantly remodeled by local cell populations in response to changing biochemical (systemic and local disease or injury) and mechanical (exercise, disuse, and overuse) stimuli. Here, we review the current understanding of matrix remodeling throughout life, focusing on formation and assembly during the postnatal period, maintenance and homeostasis during adulthood, and changes to homeostasis in natural aging. We also discuss advances in model systems and novel tools for studying collagen and non-collagenous matrix remodeling throughout life, and finally conclude by identifying key questions that have yet to be answered.

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.

The Collagen-Based Medical Device MD-Tissue Acts as a Mechanical Scaffold Influencing Morpho-Functional Properties of Cultured Human Tenocytes

Mechanotransduction is the ability of cells to translate mechanical stimuli into biochemical signals that can ultimately influence gene expression, cell morphology and cell fate. Tenocytes are responsible for tendon mechanical adaptation converting mechanical stimuli imposed during mechanical loading, thus affecting extracellular matrix homeostasis. Since we previously demonstrated that MD-Tissue, an injectable collagen-based medical compound containing swine-derived collagen as the main component, is able to affect tenocyte properties, the aim of this study was to analyze whether the effects triggered by MD-Tissue were based on mechanotransduction-related mechanisms. For this purpose, MD-Tissue was used to coat Petri dishes and cytochalasin B was used to deprive tenocytes of mechanical stimulation mediated by the actin cytoskeleton. Cell morphology, migration, collagen turnover pathways and the expression of key mechanosensors were analyzed by morphological and molecular methods. Our findings confirm that MD-Tissue affects collagen turnover pathways and favors cell migration and show that the MD-Tissue-induced effect represents a mechanical input involving the mechanotransduction machinery. Overall, MD-Tissue, acting as a mechanical scaffold, could represent an effective medical device for a novel therapeutic, regenerative and rehabilitative approach to favor tendon healing in tendinopathies.

Short- and Long-Term Exercise Results in a Differential Achilles Tendon Mechanical Response

The study was conducted to define the biomechanical response of rat Achilles tendon after a single bout of exercise and a short or long duration of daily exercise. We hypothesized that a single bout or a short duration of exercise would cause a transient decrease in Achilles tendon mechanical properties and a long duration of daily exercise would improve these properties. One hundred and thirty-six Sprague-Dawley rats were divided into cage activity (CA) or exercise (EX) groups for a single bout, short-term, or long-term exercise. Animals in single bout EX groups were euthanized, 3, 12, 24, or 48 h upon completion of a single bout of exercise (10 m/min, 1 h) on a flat treadmill. Animals in short-term EX groups ran on a flat treadmill for 3 days, 1, or 2 weeks while animals in long-term EX groups ran for 8 weeks. Tendon quasi-static and viscoelastic response was evaluated for all Achilles tendons. A single bout of exercise increased tendon stiffness after 48 h of recovery. Short-term exercise up to 1 week decreased cross-sectional area, stiffness, modulus, and dynamic modulus of the Achilles tendon. In contrast, 8 weeks of daily exercise increased stiffness, modulus, and dynamic modulus of the tendon. This study highlights the response of Achilles tendons to single and sustained bouts of exercise. Adequate time intervals are important to allow for tendon adaptations when initiating a new training regimen and overall beneficial effects to the Achilles tendon.

PAST, CURRENT AND FUTURE INTERVENTIONAL ORTHOBIOLOGICS TECHNIQUES AND HOW THEY RELATE TO REGENERATIVE REHABILITATION: A CLINICAL COMMENTARY

Interventional orthobiologics is changing the landscape of orthopedic medicine. Various methods exist for treatment of many different musculoskeletal pathologies. Candidacy for such injections remains a debated topic, and current research is underway for stratifying the patients that would be most successful for certain techniques. Described in this commentary are the various methods of interventional orthobiologic techniques available such as: prolotherapy, platelet rich plasma (PRP), mesenchymal stromal cells (MSCs), culture-expanded MSCs and amniotic-based products. Here we review the healing cascade and how this relates to the application of the various injectates and rehabilitation protocols. In conclusion, there exists orthobiologic techniques for the healing of a multitude of musculoskeletal ailments, from ligamentous instabilities/tears, tendon derangements and osteoarthritis, however candidacy grades continue to be an area for discussion as to which type of treatment is the most beneficial, and which rehabilitation protocols are required. More randomized controlled trials and comparative analyses are needed for direct correlative conclusions for which interventional orthobiologic treatment and rehabilitation protocol is best after each respective treatment.

LEVEL OF EVIDENCE

5.

Dry Needling as a Treatment Modality for Tendinopathy: a Narrative Review

PURPOSE OF REVIEW

Tendinopathy describes a combination of pain, swelling, and impaired performance of the tendon and around structures. There are various treatment options for tendinopathy with unclear efficacy. Dry needling involves inserting needles into the affected tendon, and it is thought to disrupt the chronic degenerative process and encourage localized bleeding and fibroblastic proliferation. The purpose of this review is to review the use of dry needling as a treatment modality for tendinopathy.

RECENT FINDINGS

The effectiveness of dry needling for treatment of tendinopathy has been evaluated in 3 systematic reviews, 7 randomized controlled trials, and 6 cohort studies. The following sites were studied: wrist common extensor origin, patellar tendon, rotator cuff, and tendons around the greater trochanter. There is considerable heterogeneity of the needling techniques, and the studies were inconsistent about the therapy used after the procedure. Most systematic reviews and randomized controlled trials support the effectiveness of tendon needling. There was a statistically significant improvement in the patient-reported symptoms in most studies. Some studies reported an objective improvement assessed by ultrasound. Two studies reported complications. Current research provides initial support for the efficacy of dry needling for tendinopathy treatment. It seems that tendon needling is minimally invasive, safe, and inexpensive, carries a low risk, and represents a promising area of future research. In further high-quality studies, tendon dry needling should be used as an active intervention and compared with appropriate sham interventions. Studies that compare the different protocols of tendon dry needling are also needed.

Plasma Amino Acid Concentrations After the Ingestion of Dairy and Collagen Proteins, in Healthy Active Males

Introduction: Recent evidence suggests that the consumption of essential amino acids (AA) and/or those abundantly present in collagen may have the capacity to influence the synthesis of new collagen in ligaments and tendons, when tissue perfusion is optimized (e.g., during exercise). However, little is currently known about the bioavailability of these AAs in blood after the consumption of various collagen and diary protein sources: such information is needed to develop potentially useful dietary and supplement intake strategies. Objectives: The aim of the current study was to characterize blood AA concentrations in response to consumption of collagen and dairy protein sources; specifically, maximum concentrations, the timing of maximum concentration, and total (area under the curve) exposure above baseline. Methods: A 20 g serve of various dairy and collagen proteins, and a 300 mL serve of bone broth were consumed by healthy, recreationally active males after an overnight fast. Blood samples were drawn every 20 min for a total of 180 min, for analysis of plasma AA concentrations. Total AA, essential AA and collagen specific AAs were analyzed for maximum concentration, timing of peak, and area under the curve. Results: In general, protein intake was associated with a similar increase in total and collagen specific AAs, except for collagen proteins being a superior source of glycine (683 ± 166 μmol/L) compared to 260 ± 65 μmol/L for dairy proteins (P < 0.0001), whilst dairy proteins were a superior source of leucine (267 ± 77 μmol/L) compared to 189 ± μmol/L for collagen proteins (P < 0.04). Although there were several differences in the bioavailability of hydrolysed compared to non-hydrolysed proteins, this only reached statistical significance within the dairy proteins, but not for collagen proteins. Conclusions: The intake of collagen proteins result in higher plasma peaks of glycine, whilst the intake of dairy proteins result in higher plasma peaks of leucine. This information may support further investigations, and identification of key AAs that may support exercise in the synthesis of collagen.

Clinical Improvements Are Not Explained by Changes in Tendon Structure on Ultrasound Tissue Characterization After an Exercise Program for Patellar Tendinopathy

OBJECTIVES

The aim of this study was to investigate the effects of a 4-wk in-season exercise program of isometric or isotonic exercises on tendon structure and dimensions as quantified by ultrasound tissue characterization (UTC).

DESIGN

This was a randomized clinical trial. Volleyball and basketball players (16-31 yrs, n = 29) with clinically diagnosed patellar tendinopathy were randomized to a 4-wk isometric or isotonic exercise program. The programs were designed to decrease patellar tendon pain. A baseline and 4-wk UTC scan was used to evaluate change in tendon structure.

RESULTS

No significant change in tendon structure or dimensions on UTC was detected after the exercise program despite patellar tendinopathy symptoms improving. The percentage and mean cross-sectional area of aligned fibrillar structure (echo types I + II) (Z = -0.414, P = 0.679) as well as disorganized structure (echo types III + IV) (Z = -0.370, P = 0.711) did not change over the 4-wk exercise program. Change in tendon structure and dimensions on UTC did not differ significantly between the groups.

CONCLUSION

Structural properties and dimensions of the patellar tendon on UTC did not change after a 4-wk isometric or isotonic exercise program for athletes with patellar tendinopathy in-season, despite an improvement in symptoms. It seems that structural improvements are not required for a positive clinical outcome.

Measurement of Strength Gains Using a Fascial System Exercise Program

Current fascia research is allowing for an interdisciplinary understanding of the body's anatomical, biomechanical, and neurological connectivity via the fascial network. Fascial research and its application has been validated and established in various clinical areas of research. The purpose of this study was to apply the current knowledge of the fascial system to general exercise protocols. This study involved 20 women, ages 30-60 years, who were novice weight trainers, mostly sedentary, and with no injuries, excessive pain or disease. The 10-week study compared strength gain changes between a strength training regimen control group (10) and a treatment group (10) with the same strength routine along with a fascial system exercise protocol. Statistical analysis was completed using a repeated measure design to determine differences between baseline and final measures of strength between groups. The repeated measures analysis of variance revealed no significant differences between treatment and control groups between pre and post trials. The analysis did find significant differences in strength across trials for both groups in the variables of leg press (Treatment =+62 lbs., Control = +67 lbs.), leg extension (Treatment =+61 lbs., Control = +45.5 lbs.), and chest press (Treatment =+19.5 lbs., Control = +16.5 lbs.). These results may be attributed to the control group receiving sufficient stimulus to the fascial system to produce similar results to that of the treatment group or due to training time was not sufficient to elicit an effect of the fascial training.

The mechanical and biochemical properties of tail tendon in a rat model of obesity: Effect of moderate exercise and prebiotic fibre supplementation

The worldwide trajectory of increasing obesity rates is a major health problem precipitating a rise in the prevalence of a variety of co-morbidities and chronic diseases. Tendinopathy, in weight and non-weight bearing tendons, in individuals with overweight or obesity has been linked to metabolic dysfunction resulting from obesity. Exercise and dietary fibre supplementation (DFS) are common countermeasures to combat obesity and therefore it seems reasonable to assume that they might protect tendons from structural and mechanical damage in a diet-induced obesity (DIO) model. The purpose of this study was to determine the effects of a DIO, DIO combined with moderate exercise, DIO combined with DFS (prebiotic oligofructose), and DIO combined with moderate exercise and DFS on the mechanical and biochemical properties of the rat tail tendon. Twenty-four male Sprague-Dawley rats, fed a high-fat/high-sucrose diet were randomized into a sedentary, a moderate exercise, a DFS, or a moderate exercise combined with DFS group for 12 weeks. Additionally, six lean age-matched animals were included as a sedentary control group. DIO in combination with exercise alone and with exercise and DFS reduced the Young's Modulus but not the collagen content of the rat tail tendons compared to lean control animals. However, no differences in the mechanical and biochemical properties of the rat tail tendon were detected between the DIO and the lean control group, suggesting that DIO by itself did not impact the tail tendon. It seems that longer DIO exposure periods may be needed to develop overt differences in our DIO model.

How do tendons adapt? Going beyond tissue responses to understand positive adaptation and pathology development: A narrative review

Understanding how tendons adapt to load is crucial to understanding how training can improve performance, minimise the risk of injury and aid rehabilitation. Adaptation is the positive response of an organism or tissue to benefit its function. In tendons, numerous tissue responses to load have been identified in vivo. Changes in tendon dimensions, structure on imaging, mechanical properties, and blood flow have been reported in response to mechanical stimuli. However, research has focused on tissue level changes with little understanding of how changes at the tissue level affect the person, their athletic performance or injury risk. Tendons can have a paradoxical response to load, load can induce positive adaptation, however it is also a major factor in the development of tendon pathology and pain. Tendon pathology is a risk factor for developing symptoms, yet the high rate of asymptomatic pathology suggests that the pathological tendon must adapt to be able to tolerate load. Similarly, there is mounting evidence to suggest that tendon remodelling or repair is not necessary for a positive clinical outcome following rehabilitation, suggesting that the tendon must adapt via other mechanisms. This narrative review synthesises evidence of how normal and pathological tendons adapts to load, and how this relates to adaptation of load capacity and function of the individual.

Connective Tissue and Age-Related Diseases

We begin this chapter by describing normal characteristics of several pertinent connective tissue components, and some of the basic changes they undergo with ageing. These alterations are not necessarily tied to any specific disease or disorders, but rather an essential part of the normal ageing process. The general features of age-induced changes, such as skin wrinkles, in selected organs with high content of connective or soft tissues are discussed in the next part of the chapter. This is followed by a section dealing with age-related changes in specific diseases that fall into at least two categories. The first category encompasses common diseases with high prevalence among mostly ageing populations where both genetic and environmental factors play roles. They include but may not be limited to atherosclerosis and coronary heart disease, type II diabetes, osteopenia and osteoporosis, osteoarthritis, tendon dysfunction and injury, age-related disorders of spine and joints. Disorders where genetics plays the primary role in pathogenesis and progression include certain types of progeria, such as Werner syndrome and Hutchinson-Gilford progeria belong to the second category discussed in this chapter. These disorders are characterized by accelerated signs and symptoms of ageing. Other hereditary diseases or syndromes that arise from mutations of genes encoding for components of connective tissue and are less common than diseases included in the first group will be discussed briefly as well, though they may not be directly associated with ageing, but their connective tissue undergoes some changes compatible with ageing. Marfan and Ehlers-Danlos syndromes are primary examples of such disorders. We will probe the role of specific components of connective tissue and extracellular matrix if not in each of the diseases, then at least in the main representatives of these disorders.

Tendon Remodeling in Response to Resistance Training, Anabolic Androgenic Steroids and Aging

Exercise training (ET), anabolic androgenic steroids (AAS), and aging are potential factors that affect tendon homeostasis, particularly extracellular matrix (ECM) remodeling. The goal of this review is to aggregate findings regarding the effects of resistance training (RT), AAS, and aging on tendon homeostasis. Data were gathered from our studies regarding the impact of RT, AAS, and aging on the calcaneal tendon (CT) of rats. We demonstrated a series of detrimental effects of AAS and aging on functional and biomechanical parameters, including the volume density of blood vessel cells, adipose tissue cells, tendon calcification, collagen content, the regulation of the major proteins related to the metabolic/development processes of tendons, and ECM remodeling. Conversely, RT seems to mitigate age-related tendon dysfunction. Our results suggest that AAS combined with high-intensity RT exert harmful effects on ECM remodeling, and also instigate molecular and biomechanical adaptations in the CT. Moreover, we provide further information regarding the harmful effects of AAS on tendons at a transcriptional level, and demonstrate the beneficial effects of RT against the age-induced tendon adaptations of rats. Our studies might contribute in terms of clinical approaches in favor of the benefits of ET against tendinopathy conditions, and provide a warning on the harmful effects of the misuse of AAS on tendon development.

Effect of a Collagen-Based Compound on Morpho-Functional Properties of Cultured Human Tenocytes

Background: Greater Trochanter Pain Syndrome (GTPS) is the main reason for recalcitrant lateral hip pain. Gluteus medius and minimus tendinopathy plays a key role in this setting. An injectable medical compound containing collagen type I (MD-Tissue, Guna) has been produced with the aim to counteract the physiological and pathological degeneration of tendons. In this study we aimed at characterizing the effect of this medical compound on cultured human gluteal tenocytes, focusing on the collagen turnover pathways, in order to understand how this medical compound could influence tendon biology and healing. Methods: Tenocytes were obtained from gluteal tendon fragments collected in eight patients without any gluteal tendon pathology undergoing total hip replacement through an anterior approach. Cell proliferation and migration were investigated by growth curves and wound healing assay, respectively. The expression of genes and proteins involved in collagen turnover were analysed by real-time PCR, Slot blot and SDS-zymography. Results: Our data show that tenocytes cultured on MD-Tissue, compared to controls, have increased proliferation rate and migration potential. MD-Tissue induced collagen type I (COL-I) secretion and mRNA levels of tissue inhibitor of matrix metalloproteinases (MMP)-1 (TIMP-1). Meanwhile, lysyl hydroxylase 2b and matrix metalloproteinases (MMP)-1 and -2, involved, respectively, in collagen maturation and degradation, were not affected. Conclusions: Considered as a whole, our results suggest that MD-Tissue could induce in tenocytes an anabolic phenotype by stimulating tenocyte proliferation and migration and COL-I synthesis, maturation, and secretion, thus favouring tendon repair. In particular, based on its effect on gluteal tenocytes, MD-Tissue could be effective in the discouraging treatment of GTPS. From now a rigorous clinical investigation is desirable to understand the real clinical potentials of this compound.

SUPRASPINATUS TENDON PATHOMECHANICS: A CURRENT CONCEPTS REVIEW

BACKGROUND AND PURPOSE

Tendinopathy of the supraspinatus muscle is a frequent cause of shoulder pain. Although it is a common condition, the pathophysiology is not fully understood. The purpose of this clinical commentary is to provide an overview of the pathophysiology of supraspinatus tendinopathy and discuss the conservative treatment solutions.

DESCRIPTION

Supraspinatus tendinopathy is thought to be caused by both intrinsic, and extrinsic factors. Structural and biological changes happen when tendinopathy develops. Cellular and extracellular modifications characterize tendon healing stages that continue over time. Assessment is paramount in order to differentiate the structure involved, and to offer a proper treatment solution.

RELATION TO CLINICAL PRACTICE

Knowledge of the general concepts regarding the development of supraspinatus tendinopathy, and of the healing process should guide physiotherapists when proposing treatment options. Physical modalities commonly utilized for supraspinatus tendinopathy such as: laser, ultrasound, and shock-wave therapy have little and contradictory evidence. Exercise in form of eccentric training may be considered as it seems to have beneficial effects, however, more research is needed.

Tendon Structure Quantified using Ultrasound Imaging Differs Based on Location and Training Type

Achilles tendinopathy is ten-times more common amongst running athletes compared to age-matched peers. Load induced tendon remodeling and its progression in an at-risk population of developing symptomatic tendinopathy is not well understood. The purpose of this study was to prospectively characterize Achilles and patellar tendon structure in competitive collegiate distance runners over different competitive seasons using quantitative ultrasound imaging. Twenty-two collegiate cross country runners and eleven controls were examined for this study. Ultrasound images of bilateral Achilles and patellar tendons were obtained near the start and end of the collegiate cross country season and the conclusion outdoor track season. Collagen organization, mean echogenicity, tendon thickness, and neovascularity were determined using well established image processing techniques. Achilles tendon collagen was less aligned in runners compared to controls (28% greater) but improved slightly (7% decrease) after the completion of the track season. Conversely, patellar tendons in runners were similar to control tendon throughout the cross-country season but underwent collagen alignment (17% decrease) and tendon hypertrophy (21% increase). Our findings indicate that Achilles tendon structure in trained runners differ structurally to control tendons but is stable throughout training while patellar tendon structure changes in response to the transition in training volume between cross country and track seasons. These findings expand upon prior reports that some degree of tendon remodeling may act as a protective adaptation for sport specific loading.

A Multicenter Large-Sample Shear Wave Ultrasound Elastographic Study of the Achilles Tendon in Chinese Adults

OBJECTIVES

The changes in the viscoelasticity of the Achilles tendon are related to tendinopathy. Therefore, constructing a data model in the healthy population is essential to understanding the key factors affecting the viscoelasticity of the Achilles tendon. The purpose of our research was to obtain large sample data, construct a data model, and determine parameters that affect the elastic modulus of the Achilles tendon in healthy Chinese adults.

METHODS

We designed a prospective multicenter clinical trial to evaluate the viscoelasticity of the Achilles tendon by using shear wave elastography. A total of 1165 healthy adult participants from 17 Chinese hospitals were recruited for the assessment. The necessary parameters (age, height, weight, and body mass index) were recorded. The elastic modulus (Young modulus) was obtained from the middle of the Achilles tendon and calculated with feet in naturally relaxed, dorsal, and plantar positions. The thickness and perimeter of the Achilles tendon were measured via cross section on the same site. A multiple linear regression was performed to find the key factors affecting the Young modulus of the Achilles tendon.

RESULTS

The Young modulus of the left Achilles tendon in the natural relaxed position followed a normal distribution (P > .05) with a mean ± SD of 374.24 ± 106.12 kPa. The regression equations showed a positive correlation between the Young modulus and weight and a negative correlation between the Young modulus and the circumference or thickness of the left Achilles tendon (P < .05).

CONCLUSIONS

The Young modulus of the Achilles tendon as measured by shear wave elastography is related to body weight as well as the perimeter or thickness of the tendon.

Achilles tendon structure differs between competitive distance runners and nonrunners despite no clinical signs or symptoms of midsubstance tendinopathy

Achilles tendinopathy affects many running athletes and often leads to chronic pain and functional deficits. Although changes in tendon structure have been linked with tendinopathy, the effects of distance running on tendon structure are not well understood. Therefore, the purpose of this study was to characterize structural differences in the Achilles tendons in healthy young adults and competitive distance runners using quantitative ultrasound analyses. We hypothesized that competitive distance runners with no clinical signs or symptoms of tendinopathy would have quantitative signs of tendon damage, characterized by decreased collagen alignment and echogenicity, in addition to previous reports of thicker tendons. Longitudinal ultrasound images of the right Achilles tendon midsubstance were acquired in competitive distance runners and recreationally active adults. Collagen organization, mean echogenicity, and tendon thickness were quantified using image processing techniques. Clinical assessments confirmed that runners had no signs or symptoms of tendinopathy, and controls were only included if they had no history of Achilles tendon pain or injuries. Runner tendons were 40% less organized, 48% thicker, and 41% less echogenic compared with the control tendons ( P < 0.001). Young adults engaged in competitive distance running have structurally different tendons than recreationally active young adults.

NEW & NOTEWORTHY In this study, we quantified the Achilles tendon substructure in distance runners, and a control group of young adults, to determine whether distance running elicits structural adaptations of the tendon. We found that competitive distance runners have structurally compromised Achilles tendons despite not showing any clinical signs or symptoms of tendon injury. These findings suggest that distance running may stimulate structural changes as a protective mechanism against tendon pain and dysfunction.

The impact of loading, unloading, ageing and injury on the human tendon

A tendon transfers force from the contracting muscle to the skeletal system to produce movement and is therefore a crucial component of the entire muscle-tendon complex and its function. However, tendon research has for some time focused on mechanical properties without any major appreciation of potential cellular and molecular changes. At the same time, methodological developments have permitted determination of the mechanical properties of human tendons in vivo, which was previously not possible. Here we review the current understanding of how tendons respond to loading, unloading, ageing and injury from cellular, molecular and mechanical points of view. A mechanistic understanding of tendon tissue adaptation will be vital for development of adequate guidelines in physical training and rehabilitation, as well as for optimal injury treatment.

Imbalances in the Development of Muscle and Tendon as Risk Factor for Tendinopathies in Youth Athletes: A Review of Current Evidence and Concepts of Prevention

Tendons feature the crucial role to transmit the forces exerted by the muscles to the skeleton. Thus, an increase of the force generating capacity of a muscle needs to go in line with a corresponding modulation of the mechanical properties of the associated tendon to avoid potential harm to the integrity of the tendinous tissue. However, as summarized in the present narrative review, muscle and tendon differ with regard to both the time course of adaptation to mechanical loading as well as the responsiveness to certain types of mechanical stimulation. Plyometric loading, for example, seems to be a more potent stimulus for muscle compared to tendon adaptation. In growing athletes, the increased levels of circulating sex hormones might additionally augment an imbalanced development of muscle strength and tendon mechanical properties, which could potentially relate to the increasing incidence of tendon overload injuries that has been indicated for adolescence. In fact, increased tendon stress and strain due to a non-uniform musculotendinous development has been observed recently in adolescent volleyball athletes, a high-risk group for tendinopathy. These findings highlight the importance to deepen the current understanding of the interaction of loading and maturation and demonstrate the need for the development of preventive strategies. Therefore, this review concludes with an evidence-based concept for a specific loading program for increasing tendon stiffness, which could be implemented in the training regimen of young athletes at risk for tendinopathy. This program incorporates five sets of four contractions with an intensity of 85–90% of the isometric voluntary maximum and a movement/contraction duration that provides 3 s of high magnitude tendon strain.

Clinical Utility of Ultrasound Measurements of Plantar Fascia Width and Cross-Sectional AreaA Novel Technique

BACKGROUND

We sought to develop a standardized protocol for ultrasound (US) measurements of plantar fascia (PF) width and cross-sectional area (CSA), which may serve as additional outcome variables during US examinations of both healthy asymptomatic PF and in plantar fasciopathy and determine its interrater and intrarater reliability.

METHODS

Ten healthy individuals (20 feet) were enrolled. Participants were assessed twice by two raters each to determine intrarater and interrater reliability. For each foot, three transverse scans of the central bundle of the PF were taken at its insertion at the medial calcaneal tubercle, identified in real time on the plantar surface of the foot, using a fine wire technique. Reliability was determined using intraclass correlation coefficients (ICC), standard errors of measurement (SEM), and limits of agreement (LOA) expressed as percentages of the mean. Reliability of PF width and CSA measurements was determined using PF width and CSA measurements from one sonogram measured once and the mean of three measurements from three sonograms each measured once.

RESULTS

Ultrasound measurements of PF width and CSA showed a mean of 18.6 ± 2.0 mm and 69.20 ± 13.6 mm² respectively. Intra-reliability within both raters showed an ICC > 0.84 for width and ICC > 0.92 for CSA as well as a SEM% and LOA% < 10% for both width and CSA. Inter-rater reliability showed an ICC of 0.82 for width and 0.87 for CSA as well as a SEM% and LOA% < 10% for width and a SEM% < 10% and LOA% < 20% for CSA. Relative and absolute reliability within and between raters were higher when using the mean of three sonographs compared to one sonograph.

CONCLUSIONS

Using this novel technique, PF CSA and width may be determined reliably using measurements from one sonogram or the mean of three sonograms. Measurement of PF CSA and width in addition to already established thickness and echogenicity measurements provides additional information on structural properties of the PF for clinicians and researchers in healthy and pathologic PF.

Effects of strength, explosive and plyometric training on energy cost of running in ultra-endurance athletes

The aim of the present study was to evaluate the effects of a 12-week home-based strength, explosive and plyometric (SEP) training on the cost of running (Cr) in well-trained ultra-marathoners and to assess the main mechanical parameters affecting changes in Cr. Twenty-five male runners (38.2 ± 7.1 years; body mass index: 23.0 ± 1.1 kg·m^-2; V˙O₂max: 55.4 ± 4.0 mlO₂·kg^-1·min^-1) were divided into an exercise (EG = 13) and control group (CG = 12). Before and after a 12-week SEP training, Cr, spring-mass model parameters at four speeds (8, 10, 12, 14 km·h^-1) were calculated and maximal muscle power (MMP) of the lower limbs was measured. In EG, Cr decreased significantly (p < .05) at all tested running speeds (-6.4 ± 6.5% at 8 km·h^-1; -3.5 ± 5.3% at 10 km·h^-1; -4.0 ± 5.5% at 12 km·h^-1; -3.2 ± 4.5% at 14 km·h^-1), contact time (t_c) increased at 8, 10 and 12 km·h^-1 by mean +4.4 ± 0.1% and t_a decreased by -25.6 ± 0.1% at 8 km·h^-1 (p < .05). Further, inverse relationships between changes in Cr and MMP at 10 (p = .013; r = -0.67) and 12 km·h^-1 (p < .001; r = -0.86) were shown. Conversely, no differences were detected in the CG in any of the studied parameters. Thus, 12-week SEP training programme lower the Cr in well-trained ultra-marathoners at submaximal speeds. Increased t_c and an inverse relationship between changes in Cr and changes in MMP could be in part explain the decreased Cr. Thus, adding at least three sessions per week of SEP exercises in the normal endurance-training programme may decrease the Cr.

Moderate treadmill running exercise prior to tendon injury enhances wound healing in aging rats

The effect of exercise on wound healing in aging tendon was tested using a rat moderate treadmill running (MTR) model. The rats were divided into an MTR group that ran on a treadmill for 4 weeks and a control group that remained in cages. After MTR, a window defect was created in the patellar tendons of all rats and wound healing was analyzed. We found that MTR accelerated wound healing by promoting quicker closure of wounds, improving the organization of collagen fibers, and decreasing senescent cells in the wounded tendons when compared to the cage control. MTR also lowered vascularization, increased the numbers of tendon stem/progenitor cells (TSCs) and TSC proliferation than the control. Besides, MTR significantly increased the expression of stem cell markers, OCT-4 and Nanog, and tenocyte genes, Collagen I, Collagen III and tenomodulin, and down-regulated PPAR-γ, Collagen II and Runx-2 (non-tenocyte genes). These findings indicated that moderate exercise enhances healing of injuries in aging tendons through TSC based mechanisms, through which exercise regulates beneficial effects in tendons. This study reveals that appropriate exercise may be used in clinics to enhance tendon healing in aging patients.

Vitamin C-enriched gelatin supplementation before intermittent activity augments collagen synthesis

BACKGROUND

Musculoskeletal injuries are the most common complaint in active populations. More than 50% of all injuries in sports can be classified as sprains, strains, ruptures, or breaks of musculoskeletal tissues. Nutritional and/or exercise interventions that increase collagen synthesis and strengthen these tissues could have an important effect on injury rates.

OBJECTIVE

This study was designed to determine whether gelatin supplementation could increase collagen synthesis.

DESIGN

Eight healthy male subjects completed a randomized, double-blinded, crossover-design study in which they consumed either 5 or 15 g of vitamin C-enriched gelatin or a placebo control. After the initial drink, blood was taken every 30 min to determine amino acid content in the blood. A larger blood sample was taken before and 1 h after consumption of gelatin for treatment of engineered ligaments. One hour after the initial supplement, the subjects completed 6 min of rope-skipping to stimulate collagen synthesis. This pattern of supplementation was repeated 3 times/d with ≥6 h between exercise bouts for 3 d. Blood was drawn before and 4, 24, 48, and 72 h after the first exercise bout for determination of amino-terminal propeptide of collagen I content.

RESULTS

Supplementation with increasing amounts of gelatin increased circulating glycine, proline, hydroxyproline, and hydroxylysine, peaking 1 h after the supplement was given. Engineered ligaments treated for 6 d with serum from samples collected before or 1 h after subjects consumed a placebo or 5 or 15 g gelatin showed increased collagen content and improved mechanics. Subjects who took 15 g gelatin 1 h before exercise showed double the amino-terminal propeptide of collagen I in their blood, indicating increased collagen synthesis.

CONCLUSION

These data suggest that adding gelatin to an intermittent exercise program improves collagen synthesis and could play a beneficial role in injury prevention and tissue repair. This trial was registered at the Australian New Zealand Clinical Trials Registry as ACTRN12616001092482.

Functional weight-bearing mobilization after Achilles tendon rupture enhances early healing response: a single-blinded randomized controlled trial

PURPOSE

Functional weight-bearing mobilization may improve repair of Achilles tendon rupture (ATR), but the underlying mechanisms and outcome were unknown. We hypothesized that functional weight-bearing mobilization by means of increased metabolism could improve both early and long-term healing.

METHODS

In this prospective randomized controlled trial, patients with acute ATR were randomized to either direct post-operative functional weight-bearing mobilization (n = 27) in an orthosis or to non-weight-bearing (n = 29) plaster cast immobilization. During the first two post-operative weeks, 15°-30° of plantar flexion was allowed and encouraged in the functional weight-bearing mobilization group. At 2 weeks, patients in the non-weight-bearing cast immobilization group received a stiff orthosis, while the functional weight-bearing mobilization group continued with increased range of motion. At 6 weeks, all patients discontinued immobilization. At 2 weeks, healing metabolites and markers of procollagen type I (PINP) and III (PIIINP) were examined using microdialysis. At 6 and 12 months, functional outcome using heel-rise test was assessed.

RESULTS

Healing tendons of both groups exhibited increased levels of metabolites glutamate, lactate, pyruvate, and of PIIINP (all p < 0.05). Patients in functional weight-bearing mobilization group demonstrated significantly higher concentrations of glutamate compared to the non-weight-bearing cast immobilization group (p = 0.045).The upregulated glutamate levels were significantly correlated with the concentrations of PINP (r = 0.5, p = 0.002) as well as with improved functional outcome at 6 months (r = 0.4; p = 0.014). Heel-rise tests at 6 and 12 months did not display any differences between the two groups.

CONCLUSIONS

Functional weight-bearing mobilization enhanced the early healing response of ATR. In addition, early ankle range of motion was improved without the risk of Achilles tendon elongation and without altering long-term functional outcome. The relationship between functional weight-bearing mobilization-induced upregulation of glutamate and enhanced healing suggests novel opportunities to optimize post-operative rehabilitation.