Life-long endurance running is associated with reduced glycation and mechanical stress in connective tissue

Structure and function of Achilles and patellar tendons following moderate slow resistance training in young and old men

The aim of this study was to investigate the effect of aging and resistance training with a moderate load on the size and mechanical properties of the patellar (PT) and Achilles tendon (AT) and their associated aponeuroses; medial gastrocnemius (MG) and vastus lateralis (VL). Young (Y55; 24.8 ± 3.8 yrs, n = 11) and old men (O55; 70.0 ± 4.6 yrs, n = 13) were assigned to undergo a training program (12 weeks; 3 times/week) of moderate slow resistance training [55% of one repetition maximum (RM)] of the triceps surae and quadriceps muscles. Tendon dimensions were assessed using 1.5 T magnetic resonance imaging before and after 12 weeks. AT and PT cross sectional area (CSA) were determined every 10% of tendon length. Mechanical properties of the free AT, MG aponeurosis, PT, and VL aponeurosis were assessed using ultrasonography (deformation) and tendon force measurements. CSA of the AT but not PT was greater in O55 compared with Y55. At baseline, mechanical properties were generally lower in O55 than Y55 for AT, MG aponeurosis and VL aponeurosis (Young's modulus) but not for PT. CSA of the AT and PT increased equally in both groups following training. Further, for a given force, stiffness and Young's modulus also increased equally for VL aponeurosis and AT, for boths groups. The present study highlights that except for the PT, older men have lower tendon (AT, MG aponeurosis, and VL aponeurosis) mechanical properties than young men and 12-weeks of moderate slow resistance training appears sufficient to improve tendon size and mechanical adaptations in both young and older men. New and Noteworthy: These novel findings suggest that short-term moderate slow resistance training induces equal improvements in tendon size and mechanics regardless of age.

Greater Protein Intake Emphasizing Lean Beef Does Not Affect Resistance Training-Induced Adaptations in Skeletal Muscle and Tendon of Older Women: A Randomized Controlled Feeding Trial

BACKGROUND

Although experimental research supports that resistance training (RT), especially with greater dietary protein intake, improves muscle mass and strength in older adults, comparable research on tendons is needed.

OBJECTIVES

We assessed the effects of a protein-rich diet emphasizing lean beef, compared with 2 control diets, on RT-induced changes in skeletal muscle and tendon size and strength in older women.

METHODS

We randomly assigned women [age: 66 ± 1 y, body mass index (BMI): 28 ± 1] to groups that consumed 1) 0.8 g total protein/kg body weight/day from mixed food sources (normal protein control, n = 16); 2) 1.4 g/kg/d protein from mixed food sources (high protein control, n = 17); or 3) 1.4 g/kg/d protein emphasizing unprocessed lean beef (high protein experimental group, n = 16). Participants were provided with all foods and performed RT 3 times/wk, 70% of 1-repetition maximum for 12 wk. We measured quadriceps muscle volume via magnetic resonance imaging (MRI). We estimated patellar tendon biomechanical properties and cross-sectional area (CSA) using ultrasound and MRI.

RESULTS

Dietary intake did not influence RT-induced increases in quadriceps strength (P < 0.0001) or muscle volume (P < 0.05). We noted a trend for an RT effect on mean tendon CSA (P = 0.07), with no differences among diets (P > 0.05). Proximal tendon CSA increased with RT (P < 0.05) with no difference between dietary groups (P > 0.05). Among all participants, midtendon CSA increased with RT (P ≤ 0.05). We found a decrease in distal CSA in the 0.8 g group (P < 0.05) but no change in the 1.4 g group (P > 0.05). Patellar tendon MRI signal or biomechanical properties were unchanged.

CONCLUSIONS

Our findings indicated that greater daily protein intake, emphasizing beef, did not influence RT-induced changes in quadriceps muscle strength or muscle volume of older women. Although we noted trends in tendon CSA, we did not find a statistically significant impact of greater daily protein intake from beef on tendon outcomes. This trial was registered at clinicaltrials.gov as NCT04347447.

Muscle-tendon unit design and tuning for power enhancement, power attenuation, and reduction of metabolic cost

The contractile elements in skeletal muscle fibers operate in series with elastic elements, tendons and potentially aponeuroses, in muscle-tendon units (MTUs). Elastic strain energy (ESE), arising from either work done by muscle fibers or the energy of the body, can be stored in these series elastic elements (SEEs). MTUs vary considerably in their design in terms of the relative lengths and stiffnesses of the muscle fibers and SEEs, and the force and work generating capacities of the muscle fibers. However, within an MTU it is thought that contractile and series elastic elements can be matched or tuned to maximize ESE storage. The use of ESE is thought to improve locomotor performance by enhancing contractile element power during activities such as jumping, attenuating contractile element power during activities such as landing, and reducing the metabolic cost of movement during steady-state activities such as walking and running. The effectiveness of MTUs in these potential roles is contingent on factors such as the source of mechanical energy, the control of the flow of energy, and characteristics of SEE recoil. Hence, we suggest that MTUs specialized for ESE storage may vary considerably in the structural, mechanical, and physiological properties of their components depending on their functional role and required versatility.

Towards modern understanding of the Achilles tendon properties in human movement research

The Achilles tendon (AT) is the strongest tendon in humans, yet it often suffers from injury. The mechanical properties of the AT afford efficient movement, power amplification and power attenuation during locomotor tasks. The properties and the unique structure of the AT as a common tendon for three muscles have been studied frequently in humans using in vivo methods since 1990's. As a part of the celebration of 50 years history of the International Society of Biomechanics, this paper reviews the history of the AT research focusing on its mechanical properties in humans. The questions addressed are: What are the most important mechanical properties of the Achilles tendon, how are they studied, what is their significance to human movement, and how do they adapt? We foresee that the ongoing developments in experimental methods and modeling can provide ways to advance knowledge of the complex three-dimensional structure and properties of the Achilles tendon in vivo, and to enable monitoring of the loading and recovery for optimizing individual adaptations.

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.

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.

Impact of aging on tendon homeostasis, tendinopathy development, and impaired healing

Aging is a complex and progressive process where the tissues of the body demonstrate a decreased ability to maintain homeostasis. During aging, there are substantial cellular and molecular changes, with a subsequent increase in susceptibility to pathological degeneration of normal tissue function. In tendon, aging results in well characterized alterations in extracellular matrix (ECM) structure and composition. In addition, the cellular environment of aged tendons is altered, including a marked decrease in cell density and metabolic activity, as well as an increase in cellular senescence. Collectively, these degenerative changes make aging a key risk factor for the development of tendinopathies and can increase the frequency of tendon injuries. However, inconsistencies in the extent of age-related degenerative impairments in tendons have been reported, likely due to differences in how "old" and "young" age-groups have been defined, differences between anatomically distinct tendons, and differences between animal models that have been utilized to study the impact of aging on tendon homeostasis. In this review, we address these issues by summarizing data by well-defined age categories (young adults, middle-aged, and aged) and from anatomically distinct tendon types. We then summarize in detail how aging affects tendon mechanics, structure, composition, and the cellular environment based on current data and underscore what is currently not known. Finally, we discuss gaps in the current understanding of tendon aging and propose key avenues for future research that can shed light on the specific mechanisms of tendon pathogenesis due to aging.

Tendon Aging

Tendons are mechanosensitive connective tissues responsible for the connection between muscles and bones by transmitting forces that allow the movement of the body, yet, with advancing age, tendons become more prone to degeneration followed by injuries. Tendon diseases are one of the main causes of incapacity worldwide, leading to changes in tendon composition, structure, and biomechanical properties, as well as a decline in regenerative potential. There is still a great lack of knowledge regarding tendon cellular and molecular biology, interplay between biochemistry and biomechanics, and the complex pathomechanisms involved in tendon diseases. Consequently, this reflects a huge need for basic and clinical research to better elucidate the nature of healthy tendon tissue and also tendon aging process and associated diseases. This chapter concisely describes the effects that the aging process has on tendons at the tissue, cellular, and molecular levels and briefly reviews potential biological predictors of tendon aging. Recent research findings that are herein reviewed and discussed might contribute to the development of precision tendon therapies targeting the elderly population.

Usefulness of Skin Autofluorescence as a Biomarker of Acute Oxidative Stress in Young Male Japanese Long-Distance Runners: A Cross-Sectional Study

Chronic oxidative stress in long-distance runners adversely affects conditioning. It is important to objectively assess and monitor oxidative stress, but measuring oxidative stress can be invasive or require skill to measure. Therefore, this study aimed to verify whether skin autofluorescence (SAF), a non-invasive, rapid, and easily calculable metric for calculating advanced glycation end products (AGEs), is useful as an oxidative stress biomarker. The subjects were 50 young Japanese male long-distance runners (aged 20.2 ± 1.2 years); 35 average-sized male university students (aged 19.8 ± 1.1 years) served as controls. The interactions and relationships between SAF and plasma pentosidine and oxidative stress markers (reactive oxygen metabolite-derived compounds [d-ROMs], biological antioxidant potential [BAP], and the BAP/d-ROMs ratio) in runners were examined, and SAF in the runners and controls was compared. The results suggest that plasma pentosidine in runners is associated with oxidative stress markers and that it can assess oxidative stress. However, as SAF was not associated with oxidative stress markers, it was not validated as one. In future, clarifying the factors affecting SAF may also clarify the relationship between SAF, plasma pentosidine, and oxidative stress markers.

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.

Role of Knee and Ankle Extensors' Muscle-Tendon Properties in Dynamic Balance Recovery from a Simulated Slip

Participants exposed to a simulated slip with forward loss of balance (FLB) develop large lower limb joint moments which may be a limiting factor for those whose muscle-tendon units’ (MTUs) properties are deteriorated. Whether the age-related decline in these properties limits participants’ capacity to recover their balance following a slip with FLB remains unclear. We combined isokinetic dynamometry, ultrasound and EMG to understand how knee extensor and ankle plantarflexor muscle strength and power, rate of moment development, electromechanical delay, and tendon stiffness affected the balance of young (25.3 ± 3.9 years) and older adults (62.8 ± 7.1 years) when recovering from a single slip with FLB triggered whilst walking on a split-belt instrumented treadmill. Except for the patellar tendon’s stiffness, knee extensor and ankle plantarflexor electromechanical delays, older adults’ MTUs properties were deteriorated compared to those of young participants (p < 0.05). We found no significant relationship between age or the MTUs properties of participants and balance recovery. These findings provide additional support that neither maximal nor explosive strength training are likely to be successful in preventing a fall for healthy older adults, and that other type of interventions, such as task-specific training that has already proved efficacious in reducing the risk of falling, should be developed.

Regulators of collagen crosslinking in developing and adult tendons

Tendons are collagen-rich musculoskeletal tissues that possess the mechanical strength needed to transfer forces between muscles and bones. The mechanical development and function of tendons are impacted by collagen crosslinks. However, there is a limited understanding of how collagen crosslinking is regulated in tendon during development and aging. Therefore, the objective of the present review was to highlight potential regulators of enzymatic and non-enzymatic collagen crosslinking and how they impact tendon function. The main collagen crosslinking enzymes include lysyl oxidase (LOX) and the lysyl oxidase-like isoforms (LOXL), whereas non-enzymatic crosslinking is mainly mediated by the formation of advanced glycation end products (AGEs). Regulators of the LOX and LOXL enzymes may include mechanical stimuli, mechanotransducive cell signaling pathways, sex hormones, transforming growth factor (TGF)β family, hypoxia, and interactions with intracellular or extracellular proteins. AGE accumulation in tendon is due to diabetic conditions and aging, and can be mediated by diet and mechanical stimuli. The formation of these enzymatic and non-enzymatic collagen crosslinks plays a major role in tendon biomechanics and in the mechanisms of force transfer. A more complete understanding of how enzymatic and non-enzymatic collagen crosslinking is regulated in tendon will better inform tissue engineering and regenerative therapies aimed at restoring the mechanical function of damaged tendons.

A physically active lifestyle is related to a lower level of skin autofluorescence in a large population with chronic-disease (LifeLines cohort)

BACKGROUND

Physical activity (PA) has substantial health benefits and is important in combatting chronic diseases, which have been associated with elevated levels of advanced glycation endproducts (AGEs). AGEs play a role in the aging process, and an association between PA and AGEs has been reported. We aimed to investigate the relationship between PA and AGE accumulation in a general population and in a population with chronic diseases.

METHODS

This large cross-sectional population study used data from adult participants in the LifeLines project, with participant information drawn from the LifeLines database as well data from patients with diabetes mellitus or renal and/or cardiovascular diseases. Tissue AGE accumulation was assessed non-invasively by skin-autofluorescence (SAF) using an AGE reader (DiagnOptics Technologies BV, Groningen, the Netherlands). PA was assessed using the short questionnaire to assess health-enhancing physical activity (SQUASH). Multivariate linear regression analyses were adjusted for age, body mass index, sex, and smoking status.

RESULTS

Data from 63,452 participants (general population n = 59,177, chronic disease n = 4275) were analyzed. The general population was significantly younger (43.58 ± 11.77 years, mean ± SD) and had significantly lower SAF (1.90 ± 0.42 arbitrary units (AU)) compared to the population with chronic disease (age: 55.51 ± 12.07 years; SAF: 2.27 ± 0.51 AU). In the group with chronic disease, more hours of moderate to vigorous physical activities per week were associated with lower SAF (β = -0.002, 95% confidence interval (95%CI): -0.002 to -0.001). For the general population, there was no association between hours of moderate to vigorous activity and SAF (β = 3.2  × 10^-5, 95%CI: 0.000-0.001, p = 0.742). However, there was an association in the general population between total hours of PA per week and SAF (β = 4.2 × 10^-4, 95%CI: 0.000-0.001, p < 0.001), but this association was not found in the chronic disease population (β = -3.2 × 10^-4, 95%CI: -0.001 to 0.000, p = 0.347).

CONCLUSION

Our study demonstrates that an inverse relationship exists between PA and AGE accumulation in the population with chronic disease. More hours of moderate to vigorous activity is associated with a significantly decreased SAF. More PA is associated with a lower SAF, even after adjusting for the established predictors (age, body mass index, smoking status, and sex). Our findings could help to promote health and prolong longevity.

Shear-stress sensing by PIEZO1 regulates tendon stiffness in rodents and influences jumping performance in humans

Athletic performance relies on tendons, which enable movement by transferring forces from muscles to the skeleton. Yet, how load-bearing structures in tendons sense and adapt to physical demands is not understood. Here, by performing calcium (Ca²⁺) imaging in mechanically loaded tendon explants from rats and in primary tendon cells from rats and humans, we show that tenocytes detect mechanical forces through the mechanosensitive ion channel PIEZO1, which senses shear stresses induced by collagen-fibre sliding. Through tenocyte-targeted loss-of-function and gain-of-function experiments in rodents, we show that reduced PIEZO1 activity decreased tendon stiffness and that elevated PIEZO1 mechanosignalling increased tendon stiffness and strength, seemingly through upregulated collagen cross-linking. We also show that humans carrying the PIEZO1 E756del gain-of-function mutation display a 13.2% average increase in normalized jumping height, presumably due to a higher rate of force generation or to the release of a larger amount of stored elastic energy. Further understanding of the PIEZO1-mediated mechanoregulation of tendon stiffness should aid research on musculoskeletal medicine and on sports performance.

Adherence to Mediterranean diet and advanced glycation endproducts in patients with diabetes

BACKGROUND

In recent years, American Diabetes Association started to strongly advocate the Mediterranean diet (MD) over other diets in patients with diabetes mellitus (DM) because of its beneficial effects on glycemic control and cardiovascular (CV) risk factors. Tissue levels of advanced glycation endproducts (AGEs) emerged as an indicator of CV risk in DM. Skin biopsy being invasive, the use of AGE Reader has been shown to reflect tissue AGEs reliably.

AIM

To examine the association between adherence to MD and AGEs in patients with DM type II.

METHODS

This cross-sectional study was conducted on 273 patients with DM type II. A survey questionnaire was composed of 3 separate sections. The first part of the questionnaire included general data and the habits of the participants. The second part aimed to assess the basic parameters of participants’ diseases and associated conditions. The third part of the questionnaire was the Croatian version of the 14-item MD service score (MDSS). AGEs levels and associated CV risk were measured using AGE Reader (DiagnOptics Technologies BV, Groningen, The Netherlands).

RESULTS

A total of 27 (9.9%) patients fulfilled criteria for adherence to MD, with a median score of 8.0 (6.0-10.0). Patients with none/limited CV risk had significantly higher percentage of MD adherence in comparison to patients with increased/definite CV risk (15.2% vs 6.9%, P = 0.028), as well as better adherence to guidelines for nuts (23.2% vs 12.6%, P = 0.023) and legumes (40.4% vs 25.9%, P = 0.013) consumption. Higher number of patients with glycated hemoglobin (HbA1c) < 7% adhered to MD when compared to patients with HbA1c > 7% (14.9% vs 7.3%, P = 0.045). Moreover, those patients followed the MDSS guidelines for eggs (33.0% vs 46.8%, P = 0.025) and wine (15.6% vs 29.8%, P = 0.006) consumption more frequently. MDSS score had significant positive correlation with disease duration (r = 0.179, P = 0.003) and negative correlation with body mass index (BMI) values (r = -0.159, P = 0.008). In the multiple linear regression model, BMI (β ± SE, -0.09 ± 0.04, P = 0.037) and disease duration (β ± SE, 0.07 ± 0.02, P < 0.001) remained significant independent correlates of the MDSS score. Patients with HbA1c > 7% think that educational programs on nutrition would be useful for patients in significantly more cases than patients with HbA1c < 7% (98.9% vs 92.6%, P = 0.009).

CONCLUSION

Although adherence to MD was very low among people with diabetes, we demonstrated that adherence to MD is greater in patients with lower CV risk, longer disease duration, and well-controlled glycaemia.

Age-related declines in muscle and respiratory function are proportionate to declines in performance in Master Track Cyclists

PURPOSE

Respiratory and musculoskeletal function decline with age, irrespective of physical activity levels. Previous work has suggested that the age-related rate of decline in function of these two systems might be similar, but it is not known to what extent each system contributes to decreasing performance in ageing master cyclists. Therefore, the purposes of this study are (1) whether the age-related rate of decline in respiratory function, respiratory muscle strength, muscle architecture, muscle function, haemoglobin concentration, haematocrit and performance in master cyclists is uniform and (2) which parameters contribute most to the reduction in performance with age.

METHODS

Master cyclists were recruited during the Track Cycling Masters World Championship 2019 in Manchester. Respiratory function and respiratory muscle strength were determined using spirometry and a mouth pressure device, respectively. Muscle architecture was determined using ultrasonography, and muscle function by countermovement jump.

RESULTS

Forced expiratory volume in the first second, forced vital capacity, fascicle length, muscle thickness, take-off velocity, jump power, jump power per body mass, handgrip strength, haemoglobin concentration and performance correlated negatively with age (p ≤ 0.043). The age-related rate of decline did not differ significantly between parameters (p = 0.124), but it was slower for haemoglobin concentration (p = 0.041). Take-off velocity was the major determinant of performance in 200, 500 and 2000 m track cycling disciplines (R²_adj = 0.675, 0.786 and 0.769, respectively; p < 0.001).

CONCLUSION

Age-related decline in respiratory and muscle system is accompanied by a similar rate of decline in performance. The major contribution to the age-related decline of performance is reduced muscle function, specifically take-off velocity.

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.

Muscle and tendon adaptations to moderate load eccentric vs. concentric resistance exercise in young and older males

Resistance exercise training (RET) is well-known to counteract negative age-related changes in both muscle and tendon tissue. Traditional RET consists of both concentric (CON) and eccentric (ECC) contractions; nevertheless, isolated ECC contractions are metabolically less demanding and, thus, may be more suitable for older populations. However, whether submaximal (60% 1RM) CON or ECC contractions differ in their effectiveness is relatively unknown. Further, whether the time course of muscle and tendon adaptations differs to the above is also unknown. Therefore, this study aimed to establish the time course of muscle and tendon adaptations to submaximal CON and ECC RET. Twenty healthy young (24.5 ± 5.1 years) and 17 older males (68.1 ± 2.4 years) were randomly allocated to either isolated CON or ECC RET which took place 3/week for 8 weeks. Tendon biomechanical properties, muscle architecture and maximal voluntary contraction were assessed every 2 weeks and quadriceps muscle volume every 4 weeks. Positive changes in tendon Young's modulus were observed after 4 weeks in all groups after which adaptations in young males plateaued but continued to increase in older males, suggesting a dampened rate of adaptation with age. However, both CON and ECC resulted in similar overall changes in tendon Young's modulus, in all groups. Muscle hypertrophy and strength increases were similar between CON and ECC in all groups. However, pennation angle increases were greater in CON, and fascicle length changes were greater in ECC. Notably, muscle and tendon adaptations appeared to occur in synergy, presumably to maintain the efficacy of the muscle-tendon unit.

Chronic hyperglycemia, hypercholesterolemia, and metabolic syndrome are associated with risk of tendon injury

Tendon injury is a considerable problem affecting both physically active and sedentary people. The aim of this study was to examine the relationship between markers for metabolic disorders (hyperglycemia, hypercholesterolemia, and metabolic syndrome) and the risk of developing tendon injuries requiring referral to a hospital. The Copenhagen City Heart Study is a prospective study of diabetic and non-diabetic individuals from the Danish general population with different physical activity levels. The cohort was followed for 3 years via national registers with respect to tendon injuries. Data from 5856 individuals (median age 62 years) were included. The overall incidence of tendon injury in both upper and lower extremities that required an out-patient or in-house visit to a hospital was ~5.7/1000 person years. Individuals with elevated HbA1c (glycated hemoglobin) even in the prediabetic range (HbA1c>5.7%) had a ~3 times higher risk of tendon injury in the lower extremities only, as compared to individuals with normal HbA1C levels. Hypercholesterolemia (total cholesterol>5 mmol/L) increased risk of tendon injury in the upper extremities by ~1.5 times, and individuals with metabolic syndrome had ~2.5 times higher risk of tendon injury in both upper and lower extremities. In conclusion, these data demonstrate for the first time in a large cohort with different physical activity levels that the indicators for metabolic syndrome are a powerful systemic determinant of tendon injury, and two of its components, hyperglycemia and hypercholesterolemia, each independently make tendons susceptible for damage and injury.

Explaining Variability in the Prevalence of Achilles Tendon Abnormalities: A Systematic Review With Meta-analysis of Imaging Studies in Asymptomatic Individuals

OBJECTIVE

To estimate the prevalence of, and factors associated with, Achilles tendon abnormalities observed on imaging in asymptomatic individuals.

DESIGN

Systematic review with stratified meta-analysis and meta-regression.

LITERATURE SEARCH

Embase, Scopus, MEDLINE, CINAHL, SPORTDiscus, and Web of Science were searched from 1980 to August 2020.

STUDY SELECTION CRITERIA

We included studies that reported the prevalence of Achilles tendon abnormalities, observed with any imaging modality, in an asymptomatic population. We excluded studies if participant mean age was younger than 12 years or if participants had current/previous lower-limb tendon injuries/symptoms or other systemic conditions.

DATA SYNTHESIS

Random-effects proportion meta-analysis was used to estimate prevalence. We used meta-regression for continuous variables (mean age and body mass index [BMI], sample size, proportion of female participants) and stratified categorical variables (imaging modality and participation in physical activity) to explain between-study heterogeneity.

RESULTS

We included 91 studies (10 156 limbs, 5841 participants). The prevalence of Achilles tendon abnormalities on imaging ranged from 0% to 80% per participant. Between-study heterogeneity was high (I²>90%, P<.001), precluding data pooling. Between-study heterogeneity was partly explained by participant mean BMI (slope, 2.8% per 1-unit increase in BMI; 95% confidence interval: 0.57%, 5.03%; P = .015) and participation in physical activity per limb, and mean age of 40 years old or older (P = .022) per participant.

CONCLUSION

There was substantial variability in the prevalence of Achilles tendon abnormalities on imaging in asymptomatic individuals. Higher prevalence of abnormalities was associated with older age (40 years old or older), higher BMI, and participation in physical activity. A large proportion of heterogeneity remains unaccounted for, likely due to variations in abnormality definitions and study design. J Orthop Sports Phys Ther 2021;51(5):232-252. Epub 28 Mar 2021. doi:10.2519/jospt.2021.9970.

The combined effects of obesity and ageing on skeletal muscle function and tendon properties in vivo in men

PURPOSE

We investigated the combined impact of ageing and obesity on Achilles tendon (AT) properties in vivo in men, utilizing three classification methods of obesity.

METHOD

Forty healthy, untrained men were categorised by age (young (18-49 years); older (50-80 years)), body mass index (BMI; normal weight (≥18.5-<25); overweight (≥25-<30); obese (≥30)), body fat% (normal adipose (<28%); high adiposity (≥28%)) and fat mass index (FMI; normal (3-6); excess fat (>6-9); high fat (>9). Assessment of body composition used dual-energy X-ray absorptiometry, gastrocnemius medialis (GM)/AT properties used dynamometry and ultrasonography and endocrine profiling used multiplex luminometry.

RESULTS

Older men had lower total range of motion (ROM; -11%; P = 0.020), GM AT force (-29%; P < 0.001), stiffness (-18%; P = 0.041), Young's modulus (-22%; P = 0.011) and AT stress (-28%; P < 0.001). All three methods of classifying obesity revealed obesity to be associated with lower total ROM (P = 0.014-0.039). AT cross sectional area (CSA) was larger with higher BMI (P = 0.030). However, after controlling for age, higher BMI only tended to be associated with greater tendon stiffness (P = 0.074). Interestingly, both AT CSA and stiffness were positively correlated with body mass (r = 0.644 and r = 0.520) and BMI (r = 0.541 and r = 0.493) in the young but not older adults. Finally, negative relationships were observed between AT CSA and pro-inflammatory cytokines TNF-α, IL-6 and IL-1β.

CONCLUSIONS

This is the first study to provide evidence of positive adaptations in tendon stiffness and size in vivo resulting from increased mass and BMI in young but not older men, irrespective of obesity classification.

Morphological Characteristics of Passive and Active Structures of the Foot Across Populations With Different Levels of Physical Activity

BACKGROUND

Imaging diagnosis plays a fundamental role in the evaluation and management of injuries suffered in sports activities.

OBJECTIVE

To analyze the differences in the thickness of the Achilles tendon, patellar tendon, plantar fascia, and posterior tibial tendon in the following levels of physical activity: persons who run regularly, persons otherwise physically active, and persons with a sedentary lifestyle.

DESIGN

Cross-sectional and observational.

PARTICIPANTS

The 91 volunteers recruited from students at the university and the Triathlon Club from December 2016 to June 2019. The data were obtained (age, body mass index, and visual analog scale for quality of life together with the ultrasound measurements).

RESULTS

Tendon and ligament thickness was greater in the runners group than in the sedentary and active groups with the exception of the posterior tibial tendon. The thickness of the Achilles tendon was greater in the runners than in the other groups for both limbs (P = .007 and P = .005). This was also the case for the cross-sectional area (P < .01) and the plantar fascia at the heel insertion in both limbs (P = .034 and P = .026) and for patellar tendon thickness for the longitudinal measurement (P < .01). At the transversal level, however, the differences were only significant in the right limb (P = .040).

CONCLUSION

The thickness of the Achilles tendon, plantar fascia, and patellar tendon is greater in runners than in persons who are otherwise active or who are sedentary.

The AGE Reader: A non-invasive method to assess long-term tissue damage

AIMS

Advanced glycation endproducts (AGEs) are sugar-modified adducts which arise during non-enzymatic glycoxidative stress. These compounds may become systemically elevated in disease states, and accumulate in tissue, especially on long-lived proteins. AGEs have been implicated in various acute, and chronic diseases, stressing the need for reliable and comprehensive measuring techniques. Measurement of AGEs in tissue such as skin requires invasive skin biopsies. The AGE Reader has been developed to assess skin autofluorescence (SAF) non-invasively using the fluorescent properties of several AGEs.

RESULTS/CONCLUSION

Various studies have shown that SAF is a useful marker of disease processes associated with oxidative stress. It is prospectively associated with the development of cardiovascular events in patients with diabetes, renal or cardiovascular disease, and it predicts diabetes, cardiovascular disease, and mortality in the general population. However, when measuring SAF in individual subjects, several factors may limit the reliability of the measurement. These include endogenous factors present in the skin that absorb emission light such as melanin in dark-skinned subjects, but also factors that lead to temporal changes in SAF such as acute diseases and strenuous physical exercise associated with glycoxidative stress. Also, exogenous factors could potentially influence SAF levels inadvertently such as nutrition, and for example the application of skin care products. This review will address the AGE Reader functionality and the endogenous, and exogenous factors which potentially influence the SAF assessment in individual subjects.

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

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

Muscles adaptation to aging and training: architectural changes - a randomised trial

Background

To investigate how anatomical cross-sectional area and volume of quadriceps and triceps surae muscles were affected by ageing, and by resistance training in older and younger men, in vivo.

Methods

The old participants were randomly assigned to moderate (O55, n = 13) or high-load (O80, n = 14) resistance training intervention (12 weeks; 3 times/week) corresponding to 55% or 80% of one repetition maximum, respectively. Young men (Y55, n = 11) were assigned to the moderate-intensity strengthening exercise program. Each group received the exact same training volume on triceps surae and quadriceps group (Reps x Sets x Intensity). The fitting polynomial regression equations for each of anatomical cross-sectional area-muscle length curves were used to calculate muscle volume (contractile content) before and after 12 weeks using magnetic resonance imaging scans.

Results

Only Rectus femoris and medial gastrocnemius muscle showed a higher relative anatomical cross-sectional area in the young than the elderly on the proximal end. The old group displayed a higher absolute volume of non-contractile material than young men in triceps surae (+ 96%). After training, Y55, O55 and O80 showed an increase in total quadriceps (+ 4.3%; + 6.7%; 4.2% respectively) and triceps surae (+ 2.8%; + 7.5%; 4.3% respectively) volume. O55 demonstrated a greater increase on average gains compared to Y55, while no difference between O55 and O80 was observed.

Conclusions

Muscle loss with aging is region-specific for some muscles and uniform for others. Equivalent strength training volume at moderate or high intensities increased muscle volume with no differences in muscle volume gains for old men. These data suggest that physical exercise at moderate intensity (55 to 60% of one repetition maximum) can reverse the aging related loss of muscle mass.

Trial registration

NCT03079180 in ClinicalTrials.gov. Registration date: March 14, 2017.

The puzzling pathophysiology of frozen shoulders - a scoping review

Purpose

The pathophysiology of frozen shoulders is a complex and multifactorial process. The purpose of this review is to scope the currently available knowledge of the pathophysiology of frozen shoulders.

Methods

A systematic search was conducted in Medline, Embase and the Cochrane library. Original articles published between 1994 and October 2020 with a substantial focus on the pathophysiology of frozen shoulders were included.

Results

Out of 827 records, 48 original articles were included for the qualitative synthesis of this review. Glenohumeral capsular biopsies were reported in 30 studies. Fifteen studies investigated were classified as association studies. Three studies investigated the pathophysiology in an animal studies. A state of low grade inflammation, as is associated with diabetes, cardiovascular disease and thyroid disorders, predisposes for the development of frozen shoulder. An early immune response with elevated levels of alarmins and binding to the receptor of advance glycation end products is present at the start of the cascade. Inflammatory cytokines, of which transforming growth factor-β1 has a prominent role, together with mechanical stress stimulates Fibroblast proliferation and differentiation into myofibroblasts. This leads to an imbalance of extracellular matrix turnover resulting in a stiff and thickened glenohumeral capsule with abundance of type III collagen.

Conclusion

This scoping review outlines the complexity of the pathophysiology of frozen shoulder. A comprehensive overview with background information on pathophysiologic mechanisms is given. Leads are provided to progress with research for clinically important prognostic markers and in search for future interventions.

Level of evidence

Level V.

The role of inflammaging and advanced glycation end products on paratonia in patients with dementia

Impaired motor function is a prominent characteristic of aging. Inflammatory processes and oxidative stress from advanced glycation end-products are related to impaired motor function and could plausibly be a contributing factor to the pathogenesis of paratonia, a specific motor disorder in people with dementia. Severe paratonia results in a substantial increase of a caretaker's burden and a decrease in the quality of life. The pathogenesis of paratonia is not well understood, and no effective interventions are available to combat it. Intensive glycaemic control, reducing oxidative stress, possibly combined with a low AGE diet and AGE targeting medication may be the key method for preventing advanced glycation end-product accumulation and reducing the inflammatory burden as well as possibly postponing or preventing paratonia.

Age and training volume influence joint kinetics during running

Recently, we proposed the hypothesis that weekly running volume and preferred running pace may play a role in preserving ankle joint kinetics in middle-age runners as ankle joint kinetics were generally similar in young and middle-aged runners with similar running volume and preferred pace. To further address this hypothesis, we compared lower extremity joint kinetics between high and low training volume runners in both young and middle-aged groups. Joint kinetics calculated from 3D kinematic and ground reaction force data during over-ground running at 2.7 m·s^-1 from young and middle-aged runners who ran low or high weekly volume were analyzed. A two-factor analysis of variance was used to compare joint kinetics between age and running volume groups. Positive hip work was greater in middle-aged compared to young runners (P = .005). Plantarflexor torque (P = .009) and positive ankle work (P = .042) were greater in young compared to middle-aged runners. Positive ankle work was also greater in the high compared to the low volume group (P = .021). Finally, age by volume interactions were found for knee extensor torque (P = .024), negative knee work (P = .018), and positive knee work (P = .019) but not for ankle and hip joint kinetics. These findings suggest less distal-to-proximal difference in positive joint work with high running volume in both young and middle-aged runners as a result of greater power generation at the ankle. Given the age main effects, our findings are also the first to suggest the age-related distal-to-proximal shift in joint kinetics appears in middle-aged runners.

Association of advanced glycation end products with sarcopenia and frailty in chronic kidney disease

Prevalence of sarcopenia is high in patients with chronic kidney disease (CKD), especially in those with dialysis. Various pathological conditions related to CKD, such as chronic inflammation, insulin resistance, and endothelial dysfunction, are thought to be associated with the development and progression of sarcopenia. Advanced glycation end products (AGE), one of the representative uremic toxins, have been shown to contribute to various CKD-associated complications. This study investigated the role of AGE in frailty and sarcopenia in patients and animals with CKD, respectively. In patients undergoing dialysis, serum AGE levels were significantly increased according to the frailty status and inversely associated with physical performance and activity. AGE accumulated in the gastrocnemius muscle of 5/6 nephrectomy mice in association with morphological abnormalities, capillary rarefaction, and mitochondrial dysfunction, all of which were completely inhibited by DNA-aptamer raised against AGE. Our present findings may suggest the pathological role of AGE in sarcopenia and frailty in CKD.

Regional differences in turnover, composition, and mechanics of the porcine flexor tendon

PURPOSE

Recent data suggest that there is a lack of turnover in the core of human tendon, but it remains unknown whether there are regional differences between core and periphery of the cross section. The purpose of this project was to investigate regional differences in turnover as estimated by the accumulation of fluorescent Advanced Glycation End-products (AGEs) and regional differences in mechanical properties.

MATERIALS AND METHODS

Tendons were obtained from lean control (n = 4) and diabetic Göttingen minipigs (streptozotocin-induced, n = 6). The deep digital flexor tendon of one hind limb was separated into a proximal, central and distal part. Autofluorescence was measured in the core and periphery of the proximal and distal parts of the tendon, and mechanical properties were tested on fascicles taken from the core and periphery of the central tendon (only diabetic animals).

RESULTS

Autofluorescence was greater in the proximal than the distal part. In the distal part of the lean control animals, autofluorescent AGE accumulation was also greater in the core than the periphery. Peak modulus in the core region (704 ± 79 MPa) was higher than the periphery (466 ± 53 MPa, p < 0.05) in diabetic tendons.

CONCLUSION

Taken together, autofluorescence varied both along the length and across the tendon cross section, indicating higher turnover in the distal and peripheral regions. In addition, mechanical properties differed across the tendon cross-section.

Advanced Glycation End Product Accumulation Is Associated With Low Skeletal Muscle Mass, Weak Muscle Strength, and Reduced Bone Density: The Nagahama Study

BACKGROUND

The accumulation of advanced glycation end product (AGE) might exert deleterious effects on musculoskeletal properties. Our study aims to clarify this possible association in a large general population.

METHODS

This study investigated a general population of 9,203 patients (mean age, 57.8 years). Skeletal muscle mass was measured by bioelectrical impedance analysis, whereas accumulation of AGEs was assessed by skin autofluorescence (SAF-AGE). The muscle strength of upper and lower limbs and usual gait speed were measured in a portion of older (≥60 years of age) participants (n = 1,934). The speed of sound (SOS) in the calcaneal bone was assessed via a quantitative ultrasound technique.

RESULTS

In the total population, the frequency of low skeletal muscle mass linearly increased with the SAF-AGE quartiles (Q1: 14.2%, Q2: 16.1%, Q3: 21.1%, Q4: 24.8%; p < .001), and this association was independent of covariates including glycemic traits (Q4: odds ratio [OR] = 1.48, p < .001). The association between the highest SAF-AGE quartile and low skeletal muscle mass remained significant in the older subpopulation (OR = 1.85, p = .002). A similar but weak association was observed for low SOS (Q1: 8.9%, Q2: 8.3%, Q3: 10.4%, Q4: 12.2%; p < .001). Similar inverse associations were also observed with grip strength (OR = 1.98, p = .003), hip flexion strength (OR = 1.50, p = .012), and hip abduction strength (OR = 1.78, p = .001), but not with usual gait speed.

CONCLUSION

Accumulation of AGEs might be a deleterious factor for musculoskeletal properties.

AGE-RAGE Axis in the Pathophysiology of Chronic Lower Limb Ischemia and a Novel Strategy for Its Treatment

This review focuses on the role of advanced glycation end products (AGEs) and its cell receptor (RAGE) and soluble receptor (sRAGE) in the pathogenesis of chronic lower limb ischemia (CLLI) and its treatment. CLLI is associated with atherosclerosis in lower limb arteries. AGE-RAGE axis which comprises of AGE, RAGE, and sRAGE has been implicated in atherosclerosis and restenosis. It may be involved in atherosclerosis of lower limb resulting in CLLI. Serum and tissue levels of AGE, and expression of RAGE are elevated, and the serum levels of sRAGE are decreased in CLLI. It is known that AGE, and AGE-RAGE interaction increase the generation of various atherogenic factors including reactive oxygen species, nuclear factor-kappa B, cell adhesion molecules, cytokines, monocyte chemoattractant protein-1, granulocyte macrophage-colony stimulating factor, and growth factors. sRAGE acts as antiatherogenic factor because it reduces the generation of AGE-RAGE-induced atherogenic factors. Treatment of CLLI should be targeted at lowering AGE levels through reduction of dietary intake of AGE, prevention of AGE formation and degradation of AGE, suppression of RAGE expression, blockade of AGE-RAGE binding, elevation of sRAGE by upregulating sRAGE expression, and exogenous administration of sRAGE, and use of antioxidants. In conclusion, AGE-RAGE stress defined as a shift in the balance between stressors (AGE, RAGE) and antistressor (sRAGE) in favor of stressors, initiates the development of atherosclerosis resulting in CLLI. Treatment modalities would include reduction of AGE levels and RAGE expression, RAGE blocker, elevation of sRAGE, and antioxidants for prevention, regression, and slowing of progression of CLLI.

Physical activity and markers of glycation in older individuals: data from a combined cross-sectional and randomized controlled trial (EXAMIN AGE)

Background: Advanced glycation end products (AGEs) are protein modifications that are predominantly formed from dicarbonyl compounds that arise from glucose and lipid metabolism. AGEs and sedentary behavior have been identified as a driver of accelerated (vascular) aging. The effect of physical activity on AGE accumulation is unknown. Therefore, we investigated whether plasma AGEs and dicarbonyl levels are different across older individuals that were active or sedentary and whether plasma AGEs are affected by high-intensity interval training (HIIT).

Methods: We included healthy older active (HA, n=38, 44.7% female, 60.1 ± 7.7 years old) and healthy older sedentary (HS, n=36, 72.2% female, 60.0 ± 7.3 years old) individuals as well as older sedentary individuals with increased cardiovascular risk (SR, n=84, 50% female, 58.7 ± 6.6 years old). The SR group was randomized into a 12-week walking-based HIIT program or control group. We measured protein-bound and free plasma AGEs and dicarbonyls by ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) at baseline and after the HIIT intervention.

Results: Protein-bound AGE Nε-(carboxymethyl)lysine (CML) was lower in SR (2.6 ± 0.5 μmol/l) and HS (3.1 ± 0.5 μmol/l) than in HA (3.6 ± 0.6 μmol/l; P&lt;0.05) and remained significantly lower after adjustment for several potential confounders. None of the other glycation markers were different between HS and HA. HIIT did not change plasma AGEs and dicarbonyls in SR.

Discussion: Although lifestyle interventions may act as important modulators of cardiovascular risk, HIIT is not a potent short-term intervention to reduce glycation in older individuals, underlining the need for other approaches, such as pharmacological agents, to reduce AGEs and lower cardiovascular risk in this population.

Effect of testing temperature on the nanostructural response of tendon to tensile mechanical overload

Despite many in vitro mechanical experiments of tendon being conducted at room temperature, few assessments have been made to determine how the structural response of tendon to mechanical overload may vary with ambient temperature. We explored whether damage to the collagen nanostructure of tendon resulting from tensile rupture varies with temperature. Use of bovine tail tendons in combination with NaBH₄ crosslink stabilization treatment allowed us to probe the mechanisms underlying the observed changes. Untreated tendons and NaBH₄-stabilized tendons were pulled to rupture at temperatures of 24, 37, and 55 °C. Of nine mechanical parameters measured from the resulting stress-strain curves, only yield stress differed between the tendons tested at 37 and 24 °C. When tested at 55 °C, untreated tendons showed large reductions in ultimate strength and toughness, while NaBH₄-stabilized tendons showed smaller reductions. Differential scanning calorimetry was used to assess damage to the collagen fibril nanostructure of tendons resulting from rupture, with samples from the ruptured tendons compared to samples from the same tendons removed prior to loading. While there was indication that overload-induced molecular packing disruption to collagen fibrils may be heightened at 37 °C, statistical increases in damage compared to that occurring at 24 °C were only seen when testing was conducted at 55 °C. The results show that the temperature sensitivity of tendon to ramp loading depends on crosslinking within the tissue. In poorly crosslinked tissues, collagen may be more susceptible to mechanical damage when tested at physiologic temperature compared to room temperature. For tendons with a high density of thermally stable crosslinks, such as the human Achilles or patellar tendons, testing at room temperature should produce comparable results to testing at physiologic temperature.

Aged Tendon Stem/Progenitor Cells Are Less Competent to Form 3D Tendon Organoids Due to Cell Autonomous and Matrix Production Deficits

Tendons are dense connective tissues, which are critical for the integrity and function of our musculoskeletal system. During tendon aging and degeneration, tendon stem/progenitor cells (TSPCs) experience profound phenotypic changes with declined cellular functions that can be linked to the known increase in complications during tendon healing process in elderly patients. Tissue engineering is a promising approach for achieving a complete recovery of injured tendons. However, use of autologous cells from aged individuals would require restoring the cellular fitness prior to implantation. In this study, we applied an established cell sheet model for in vitro tenogenesis and compared the sheet formation of TSPC derived from young/healthy (Y-TSPCs) versus aged/degenerative (A-TSPCs) human Achilles tendon biopsies with the purpose to unravel differences in their potential to form self-assembled three-dimensional (3D) tendon organoids. Using our three-step protocol, 4 donors of Y-TSPCs and 9 donors of A-TSPCs were subjected to cell sheet formation and maturation in a period of 5 weeks. The sheets were then cross evaluated by weight and diameter measurements; quantification of cell density, proliferation, senescence and apoptosis; histomorphometry; gene expression of 48 target genes; and collagen type I protein production. The results revealed very obvious and significant phenotype in A-TSPC sheets characterized by being fragile and thin with poor tissue morphology, and significantly lower cell density and proliferation, but significantly higher levels of the senescence-related gene markers and apoptotic cells. Quantitative gene expression analyses at the mRNA and protein levels, also demonstrated abnormal molecular circuits in the A-TSPC sheets. Taken together, we report for the first time that A-TSPCs exhibit profound deficits in forming 3D tendon tissue organoids, thus making the cell sheet model suitable to investigate the molecular mechanisms involved in tendon aging and degeneration, as well as examining novel pharmacologic strategies for rejuvenation of aged cells.

Association of physical fitness with skin autofluorescence-derived advanced glycation end products in children

BACKGROUND

Advanced glycation end products (AGEs) accumulate with age and development of cardiovascular disease. Higher AGEs have been shown in children with diabetes but little is known about their association with lifestyle conditions in childhood. We hypothesized that BMI, blood pressure and cardiorespiratory fitness (CRF) are associated with subcutaneous AGEs formation in children.

METHODS

In this cross-sectional study, 1075 children (aged 7.2 ± 0.4 years) were screened for subcutaneous AGEs (skin autofluorescence; SAF), body mass index (BMI), blood pressure (BP), and CRF using standardized procedures. Group comparisons were performed in clinical BP and BMI categories and tertiles of CRF.

RESULTS

Children with higher physical fitness showed lower SAF (0.99(1.03;1.10)au) compared to children with low CRF (1.09(1.03;1.05)au, p < 0.001). An increase of one shuttle run stage was associated with a mean reduction in SAF of -0.033(CI: -0.042;-0.024)au, independent of BMI and BP (p < 0.001). BMI and BP were not independently associated with SAF-derived AGEs in this large cohort of primary school children.

CONCLUSIONS

Low physical fitness but not BMI and BP were associated with higher levels of AGEs. Primary prevention programs in young children may need to focus on improving physical fitness in game settings in order to reduce the growing prevalence of metabolic disorders during childhood.

Detection of Age-Related Changes in Tendon Molecular Composition by Raman Spectroscopy-Potential for Rapid, Non-Invasive Assessment of Susceptibility to Injury

The lack of clinical detection tools at the molecular level hinders our progression in preventing age-related tendon pathologies. Raman spectroscopy can rapidly and non-invasively detect tissue molecular compositions and has great potential for in vivo applications. In biological tissues, a highly fluorescent background masks the Raman spectral features and is usually removed during data processing, but including this background could help age differentiation since fluorescence level in tendons increases with age. Therefore, we conducted a stepwise analysis of fluorescence and Raman combined spectra for better understanding of the chemical differences between young and old tendons. Spectra were collected from random locations of vacuum-dried young and old equine tendon samples (superficial digital flexor tendon (SDFT) and deep digital flexor tendon (DDFT), total n = 15) under identical instrumental settings. The fluorescence-Raman spectra showed an increase in old tendons as expected. Normalising the fluorescence-Raman spectra further indicated a potential change in intra-tendinous fluorophores as tendon ages. After fluorescence removal, the pure Raman spectra demonstrated between-group differences in CH2 bending (1450 cm-1) and various ring-structure and carbohydrate-associated bands (1000-1100 cm-1), possibly relating to a decline in cellular numbers and an accumulation of advanced glycation end products in old tendons. These results demonstrated that Raman spectroscopy can successfully detect age-related tendon molecular differences.

Regional collagen turnover and composition of the human patellar tendon

Tendon pathology (tendinopathy) typically occurs in specific regions of a tendon, and growth in response to exercise also appears to be more pronounced in specific regions. In a previous study in animals we found evidence of regional differences in tendon turnover, but whether the turnover of human patellar tendon differs in different regions still remains unknown. Patellar tendons were obtained from cadavers of healthy men and women (body donation program, n = 5 donors, >60 yr of age). Samples were taken from 10 different regions along the length, width, and thickness of the tendon. Turnover was measured by ¹⁴C bomb pulse dating and also estimated from the accumulation of advanced glycation end products (AGEs) by fluorescence (340/460 nm) in addition to measurement of specific AGEs by mass spectrometry. Composition in terms of collagen, glycosaminoglycans (GAGs), and DNA was also assessed in each region. ¹⁴C results showed that all tendon regions had a similar ¹⁴C concentration, which was equal to the average atmospheric ¹⁴C concentration during the first 15 yr of the person's life. Fluorescence normalized to dry weight did not differ between regions, nor did specific AGEs. Higher GAG content was observed in the proximal and near the distal insertion of the tendon. In conclusion, healthy human patellar tendon displays no regional differences in collagen turnover throughout life.NEW & NOTEWORTHY Tendon injuries and tendinopathies typically occur in specific regions of the tendon, but the reason for this specificity is not well understood. A potential factor in injury susceptibility is tissue turnover, and previous work suggests that the tendon core has practically no turnover during adult life; however, it is not known whether this is true for other regions of the tendon. Our present results on healthy human patellar tendon clearly demonstrate that turnover does not differ between regions and thereby cannot explain differences in injury susceptibility. The findings also indicate that all regions of the tendon are formed simultaneously during skeletal maturation and do not turn over appreciably during adulthood. This is an important finding because little is known about tendon growth during maturation in humans.

Myotonometry for the evaluation of Achilles tendon mechanical properties: a reliability and construct validity study

Objective

This study evaluates the intra-rater and inter-rater reliability of the MyotonPRO and its construct validity for the assessment of Achilles tendon stiffness.

Design

Reliability and construct validity study.

Methods

Forty healthy participants were assessed using the MyotonPRO by two raters on two different occasions. Tendon was evaluated in three different positions (relaxed, 0° plantarflexion and standing) and during different isometric contractions (range 0–3 kg). Reliability was calculated using intraclass correlation coefficient (ICC and 95% CI) standard error of measurement and minimal detectable change. Construct validity was evaluated between the different positions and the different contraction intensities using Friedman test.

Results

Intra-rater reliability was very high ICC_2,k 0.87–0.98. The reliability of the 0.5 kg contraction was moderate with an ICC_2,k of 0.59. Inter-rater reliability ranged from high to very high with an ICC_2,k of 0.76–0.86. The reliability of the 0.5 kg, 1 kg contraction and the standing position was moderate with an ICC_2,k of 0.55, 0.54 and 0.56 respectively. Inter-session reliability ranged from high to very high with an ICC_2,k of 0.70–0.89. The reliability of the 0.5 kg contraction was moderate with an ICC_2,k of 0.54. Construct validity was demonstrated between different contraction levels and different positions.

Conclusion

MyotonPRO is a reliable tool for the evaluation of Achilles tendon stiffness during different contraction levels and in different positions. Construct validity was supported by changes of tendon stiffness during the explored conditions. MyotonPRO can be implemented, as a ready to use device, in the evaluation of tendon tissue mechanical properties.

Biology of Tendon Stem Cells and Tendon in Aging

Both tendon injuries and tendinopathies, particularly rotator cuff tears, increase with tendon aging. Tendon stem cells play important roles in promoting tendon growth, maintenance, and repair. Aged tendons show a decline in regenerative potential coupled with a loss of stem cell function. Recent studies draw attention to aging primarily a disorder of stem cells. The micro-environment (“niche”) where stem cells resided in vivo provides signals that direct them to metabolize, self-renew, differentiate, or remain quiescent. These signals include receptors and secreted soluble factors for cell-cell communication, extracellular matrix, oxidative stress, and vascularity. Both intrinsic cellular deficits and aged niche, coupled with age-associated systemic changes of hormonal and metabolic signals can inhibit or alter the functions of tendon stem cells, resulting in reduced fitness of these primitive cells and hence more frequent injuries and poor outcomes of tendon repair. This review aims to summarize the biological changes of aged tendons. The biological changes of tendon stem cells in aging are reviewed after a systematic search of the PubMed. Relevant factors of stem cell aging including cell-intrinsic factors, changes of microenvironment, and age-associated systemic changes of hormonal and metabolic signals are examined, with findings related to tendon stem cells highlighted when literature is available. Future research directions on the aging mechanisms of tendon stem cells are discussed. Better understanding of the molecular mechanisms underlying the functional decline of aged tendon stem cells would provide insight for the rational design of rejuvenating therapies.

[Hygieno-dietetic recommendations in the prevention of accumulation of advanced glycation products]

Advanced glycation products are proteins whose structural and functional properties have been modified by a process of oxidative glycation. The accumulation of advanced glycation products in most tissues and the oxidative stress and inflammatory reactions that accompany it, account for the multi-systemic impairment observed particularly in the elderly, diabetics and in chronic renal failure. The advanced glycation products endogenous production is continuous, related to oxidative stress, but the most important source of advanced glycation products is exogenous, mainly of food origin. Exogenous advanced glycation products are developed during the preparation of food and beverages. The advanced glycation products content is higher for animal foods, but it is mainly the preparation and cooking methods that play a decisive role. Dietary advice is based on the selection of foods and the choice of methods of preparation. Several randomized controlled studies have confirmed the favorable effect of these recommendations on serum advanced glycation products concentrations. In humans, as in animals, regular physical activity also results in a reduction of serum and tissue concentrations of advanced glycation products. There is a need for prospective clinical study to confirm the effects of hygienic and dietary recommendations that have only been appreciated, so far, on biological markers.

Advanced Glycation End Products Are Associated With Physical Activity and Physical Functioning in the Older Population

Background

Decline in physical activity and functioning is commonly observed in the older population and might be associated with biomarkers such as advanced glycation end products (AGEs). AGEs contribute to age-related decline in the function of cells and tissues in normal aging and have been found to be associated with motor function decline. The aim of this study is to investigate the association between the levels of AGEs, as assessed by skin autofluorescence, and the amount of physical activity and loss of physical functioning in older participants.

Methods

Cross-sectional data of 5,624 participants aged 65 years and older from the LifeLines Cohort Study were used. Linear regression analyses were utilized to study the associations between skin autofluorescence/AGE levels (AGE Reader), the number of physically active days (SQUASH), and physical functioning (RAND-36). A logistic regression analysis was used to study the associations between AGE levels and the compliance with the Dutch physical activity guidelines (SQUASH).

Results

A statistical significant association between AGE levels and the number of physically active days (β = -0.21, 95% confidence interval: -0.35 to -0.07, p = .004), physical functioning (β = -1.60, 95% confidence interval: -2.64 to -0.54, p = .003), and compliance with the Dutch physical activity guidelines (odds ratio = 0.76, 95% confidence interval: 0.62 to 0.94, p = .010) was revealed.

Conclusions

This study indicates that high AGE levels may be a contributing factor as well as a biomarker for lower levels of physical activity and functioning in the older population.

Comparison of Muscle Function, Bone Mineral Density and Body Composition of Early Starting and Later Starting Older Masters Athletes

Masters endurance runners can epitomize healthy aging; being reflective of the physiological processes of aging without the compounded effects of inactivity. The primary aim of the present study was to determine, using cross-sectional data, whether individuals taking up training after the age of 50 years can achieve the same level of athletic performance and musculoskeletal characteristics in their older age as those who trained all of their adult lives. A total of 150 master endurance runners [age 68 (5) years; 111 male, 39 female] were divided into early starters (training all of their adulthood) and late starters (started training after age 50 years). A comparative non-athletic group of 59 healthy older adults [age 73 (4) years; 30 female, 29 male] were additionally included for analysis. Training intensity, age-graded performance (AGP) and musculoskeletal assessments were performed. Results showed that there was no difference between athlete groups for training intensity or age-graded performance, despite the 30-year difference in training history. Body fat percentage and leg lean mass did not differ between athlete groups, but were 17% lower and 12% greater, respectively, in athlete groups compared with controls. Power normalized to body mass did not differ between any groups. Spine BMD was lower in late starters than controls, while early starters did not differ from late starters or controls. Hip BMD did not differ between any of the groups. These findings show that the Masters athletes we studied that started intense endurance running after the age of 50 years had lower body fat and higher leg lean mass compared to non-athletes. Body composition and athletic performance of the late starters was very similar to those who trained all of their adult lives.

Tendon Adaptations to Eccentric Exercise and the Implications for Older Adults

The purpose of this short review is to discuss the effects of eccentric exercise in modifying the properties of tendon tissue in healthy individuals. The tendon provides a mechanical link between muscle and bone, allowing force transmission to the skeleton, and thus, its properties have significant functional implications. Chronic resistance training has long been shown to increase the stiffness and Young's modulus of the tendon and even tendon cross-sectional area. However, as the tendon responds to the amount and/or frequency of strain, it has been previously suggested that eccentric training may result in greater adaptations due to the potential for greater training loads. Thus, this review discusses the effects of eccentric training upon healthy tendon tissue and compares these to other training modalities. Furthermore, it has been reported that the tendon may undergo adverse age-related changes. Thus, this review also discusses the potential application of eccentric resistance training as a preferential modality for counteracting these age-related changes. We conclude that while there may be no difference between contraction types for overall tendon adaptation, the lower demands of eccentric contractions may make it more appealing for the elderly population.

Effects of Long-Term Physical Activity and Diet on Skin Glycation and Achilles Tendon Structure

Advanced glycation end-products (AGEs) accumulate with aging and have been associated with tissue modifications and metabolic disease. Regular exercise has several health benefits, and the purpose of this study was to investigate the effect of regular long-term exercise and diet on skin autofluorescence (SAF) as a measure of glycation and on Achilles tendon structure. In connection with the 2017 European Masters Athletics Championships Stadia, high-level male athletes (n = 194) that had regularly trained for more than 10 years were recruited, in addition to untrained controls (n = 34). SAF was non-invasively determined using an AGE Reader. Achilles tendon thickness and vascular Doppler activity were measured by ultrasonography, and diet was assessed by a questionnaire. There was no significant difference in SAF between the athletes and controls. However, greater duration of exercise was independently associated with lower SAF. Diet also had an effect, with a more "Western" diet in youth being associated with increased SAF. Furthermore, our data demonstrated that greater Achilles tendon thickness was associated with aging and training. Together, our data indicate that long-term exercise may yield a modest reduction in glycation and substantially increase Achilles tendon size, which may protect against injury.