Tendon structural and mechanical properties do not differ between genders in a healthy community-dwelling elderly population

Ultrasonographic Evaluation of the Patellar Tendon in Cyclists, Volleyball Players, and Non-Practitioners of Sports-The Influence of Gender, Age, Height, Dominant Limb, and Level of Physical Activity

This study was based on the ultrasound evaluation of the patellar tendon dimensions in the anteroposterior and transversal approaches in sports practitioners (cyclists and volleyball players) and non-sports practitioners. Relationships between the patellar tendon length, width, and thickness with gender, age, height, the dominant limb, and level of physical activity were evaluated. The samples included cyclists, volleyball players, and non-sports practitioners between 15 and 25 years old. Individuals were positioned supine with 30 degrees of knee flexion for bilateral measurements. Sports practitioners presented with an increased patellar tendon length and thickness. There were significant differences bilaterally between sports and non-sports practitioners (p < 0.003). The three dimensions of the patellar tendon of both limbs presented correlations with the male gender (0.336 < r < 0.601), and values of moderate-to-strong intensity in the length of the patellar tendon was directly proportional to height (0.520 < r < 0.601). There was a significant difference between the patellar tendon width and age (p < 0.025). Regarding the level of physical activity, significant differences were found between low and high levels in the three dimensions bilaterally (p < 0.004). The study results indicate that gender, age, height, and level of physical activity impact patellar tendon dimensions. However, there are no associations with the dominant limb.

Clinical and Ultrasonographic Characteristics of the Achilles Tendon in Hemodialysis Patients

Background and Objectives: The early recognition of tendon alterations in chronic hemodialysis (HD) patients, an awareness of the factors that influence the condition, and active intervention have considerable clinical relevance. The aim of this study was to investigate the musculoskeletal ultrasound (MSUS) features of the Achilles tendon in chronic HD patients and determine the factors associated with tendon abnormalities. Materials and Methods: This study was conducted on 46 HD patients and 24 sex- and age-matched controls. All participants were evaluated clinically for any signs of Achilles tendon abnormalities. Then, the Achilles tendon was scanned bilaterally using MSUS. Results: Among the 92 Achilles tendons in the HD patients, there was tenderness and swelling of only two (2.2%). Regarding MSUS features, there were statistically significant higher thicknesses in the proximal end (p < 0.001), midpoint (p < 0.001), and distal end (p < 0.001) of the Achilles tendons in the HD patients when compared with the healthy controls. Tendinosis was found in 12 (13%) of the HD patients' Achilles tendons, which was statistically significant in comparison to the healthy controls (p = 0.008). There were statistically significant higher scores of structural abnormalities (p = 0.005), bone erosions (p = 0.017), and calcifications (p = 0.015) in the HD patients when compared to the healthy controls. According to the results of a univariate regression analysis, age and male gender were predictive for US abnormalities in HD patients (p = 0.002 and 0.025, respectively). Conclusions: The Achilles tendon in subjects on chronic HD showed frequent US abnormalities. These abnormalities in HD patients appear to be more related to age and gender and may be asymptomatic.

Differences in the cross-sectional area along the ankle tendons with both age and sex

Increasing age appears to influence several morphologic changes in major tendons. However, the effects of aging on the cross-sectional area (CSA) of different ankle tendons are much less understood. Furthermore, potential differences in specific tendon regions along the length of the tendons have not been investigated in detail. Sixty healthy adult participants categorized by age as young (n = 20; mean ± SD age = 22.5 ± 4.5 years), middle-age (n = 20; age = 40.6 ± 8. 0 years), or old (n = 20; age = 69.9 ± 9.1 years), from both sexes, were included. The tendon CSA of tibialis anterior (TA), tibialis posterior (TP), fibularis (FT), and Achilles (AT) was measured from T1-weighted 1.5 T MR images in incremental intervals of 10% along its length (from proximal insertion) and compared between different age groups and sexes. The mean CSA of the AT was greater in the middle-age group than both young and old participants (p < 0.01) and large effect sizes were observed for these differences (Cohen's d > 1). Furthermore, there was a significant difference in CSA in all three groups along the length of the different tendons. Region-specific differences between groups were observed in the distal portion (90% and 100% of the length), in which the FT presented greater CSA comparing middle-age to young and old (p < 0.05). In conclusion, (1) great magnitude of morpho-structural differences was discovered in the AT; (2) there are region-specific differences in the CSA of ankle tendons within the three groups and between them; and (3) there were no differences in tendon CSA between sexes.

Robust tracking for functional electrical stimulation cycling with unknown time-varying input delays: A switched systems approach

Motorized functional electrical stimulation (FES) cycling has been demonstrated to have numerous health benefits for individuals suffering from neurological disorders. FES-cycling is usually designed to track the desired trajectories in real time. However, there are input delays between the exertion of the stimulation and the corresponding muscle contraction that potentially destabilize the system and undermine training efforts. Meanwhile, muscle fatigue gives rise to a time-varying input delay and decreased force. Moreover, switching between FES and motor control can be chattering and destabilizing owing to the high frequency. This article constructs Lyapunov-Krasovskii functionals to analyze the stability and robustness of the nonlinear cycling system with time-varying input delay. A new average dwell time condition is then provided to ensure the input-to-state stability of the considered systems. Finally, numerical simulations are illustrated to verify the effectiveness of the developed controller.

Patellar Tendon Shear Wave Velocity Is Higher and has Different Regional Patterns in Elite Competitive Alpine Skiers than in Healthy Controls

Competitive alpine skiers are exposed to enormous forces acting on their bodies–particularly on the knee joint and hence the patellar tendon - during both the off-season preparation and in-season competition phases. However, factors influencing patellar tendon adaptation and regional pattern differences between alpine skiers and healthy controls are not yet fully understood, but are essential for deriving effective screening approaches and preventative countermeasures. Thirty elite competitive alpine skiers, all members of the Swiss Alpine Ski Team, and 38 healthy age-matched controls were recruited. A set of two-dimensional shear wave elastography measurements of the PT was acquired and projected into three-dimensional space yielding a volumetric representation of the shear wave velocity profile of the patellar tendon. Multivariate linear models served to quantify differences between the two cohorts and effects of other confounding variables with respect to regional shear wave velocity. A significant (p < 0.001) intergroup difference was found between skiers (mean ± SD = 10.4 ± 1.32 m/s) and controls (mean ± SD = 8.9 ± 1.59 m/s). A significant sex difference was found within skiers (p = 0.024), but no such difference was found in the control group (p = 0.842). Regional SWV pattern alterations between skiers and controls were found for the distal region when compared to the mid-portion (p = 0.023). Competitive alpine skiers exhibit higher SWV in all PT regions than healthy controls, potentially caused by long-term adaptations to heavy tendon loading. The presence of sex-specific differences in PT SWV in skiers but not in controls indicates that sex effects have load-dependent dimensions. Alterations in regional SWV patterns between skiers and controls suggest that patellar tendon adaptation is region specific. In addition to the implementation of 3D SWE, deeper insights into long-term tendon adaptation and normative values for the purpose of preventative screening are provided.

Women Have Tendons… and Tendinopathy: Gender Bias is a "Gender Void" in Sports Medicine with a Lack of Women Data on Patellar Tendinopathy-A Systematic Review

INTRODUCTION

Patellar tendinopathy is one of the most common musculoskeletal problems associated with sport. While commonly perceived as a predominantly male problem, recent epidemiological studies revealed that it also affects a large number of sport-active women. The aim of this systematic review was to understand how the available treatments apply to women affected by patellar tendinopathy.

METHODS

We analysed the available literature with a systematic review on three databases (PubMed, Cochrane, Web of Science) on February 2021, retrieving a total of 136 studies published from 1983.

RESULTS

The overall scientific field offers an astonishingly low number of data on treatment results referring to only 78 women (2%) in the entire literature. Only 5% of the retrieved articles considered focusing only or mostly on men to be a limitation.

CONCLUSIONS

Women represent only a minority of patients studied for this topic. The few documented cases are further fragmented by being related to different treatments, thus basically offering no solid evidence for results and limitations of any therapeutic approach in women. This literature analysis showed a greater gender gap than what is recognized in science and general medicine; it showed a gender blindness in sports medicine when investigating a common problem like patellar tendinopathy.

The energy of muscle contraction. IV. Greater mass of larger muscles decreases contraction efficiency

While skeletal muscle mass has been shown to decrease mass-specific mechanical work per cycle, it is not yet known how muscle mass alters contraction efficiency. In this study, we examined the effect of muscle mass on mass-specific metabolic cost and efficiency during cyclic contractions in simulated muscles of different sizes. We additionally explored how tendon and its stiffness alters the effects of muscle mass on mass-specific work, mass-specific metabolic cost and efficiency across different muscle sizes. To examine contraction efficiency, we estimated the metabolic cost of the cycles using established cost models. We found that for motor contractions in which the muscle was primarily active during shortening, greater muscle mass resulted in lower contraction efficiency, primarily due to lower mass-specific mechanical work per cycle. The addition of a tendon in series with the mass-enhanced muscle model improved the mass-specific work and efficiency per cycle with greater mass for motor contractions, particularly with a shorter excitation duty cycle, despite higher predicted metabolic cost. The results of this study indicate that muscle mass is an important determinant of whole muscle contraction efficiency.

Intramuscular pressure of human tibialis anterior muscle detects age-related changes in muscle performance

Intramuscular pressure (IMP) reflects forces produced by a muscle. Age is one of the determinants of skeletal muscle performance. The present study aimed to test whether IMP mirrors known age-related muscular changes. We simultaneously measured the tibialis anterior (TA) IMP, compound muscle action potential (CMAP), and ankle torque in thirteen older adults (60-80 years old) in vivo by applying different stimulation intensities and frequencies. We found significant positive correlations between the stimulation intensity and IMP and CMAP. Increasing stimulation frequency caused ankle torque and IMP to increase. The electromechanical delay (EMD) (36 ms) was longer than the onset of IMP (IMPD) (29 ms). Compared to the previously published data collected from young adults (21-40 years old) in identical conditions, the TA CMAP and IMP of older adults at maximum intensity of stimulation were 23.8% and 39.6% lower, respectively. For different stimulation frequencies, CMAP, IMP, as well as ankle torque of older adults were 20.5%, 24.2%, and 13.2% lower, respectively. Surprisingly, the EMD did not exhibit any difference between young and older adults and the IMPD was consistent with the EMD. Data supporting the hypotheses suggest that IMP measurement is an indicator of muscle performance in older adults.

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.

An investigation of the sex-related differences in the stiffness of the Achilles tendon and gastrocnemius muscle: Inter-observer reliability and inter-day repeatability and the effect of ankle joint motion

PURPOSE

The purpose of the present study was to investigate sex-related differences in the stiffness of the Achilles tendon and gastrocnemius muscle at rest and tensioned state. Another purpose of the study was to investigate the inter-observer reliability and inter-day repeatability of MyotonPRO, a portable myotonometer, in measuring tendon and muscle stiffness.

METHODS

The study included 73 healthy participants (19 males for the reliability and repeatability study; 24 males and 30 females for the experimental study) with an age range of 19-27 years. The stiffness of the Achilles tendon and medial gastrocnemius muscle was measured with a portable myotonometer (MyotonPRO). The stiffness measurements of the Achilles tendon and medial gastrocnemius muscle were performed at 0° and 10° of ankle joint dorsiflexion. The stiffness measurements were performed by two physiotherapists to determine the inter-observer reliability of the device. For the inter-day repeatability (or between-day precision), the same individuals were reassessed by the same examiner after a 3-day interval.

RESULTS

It was found that MyotonPRO has excellent inter-observer reliability and inter-day repeatability in measuring the stiffness of the Achilles tendon and medial gastrocnemius muscle (ICC=0.83-0.98). The stiffness of the Achilles tendon and gastrocnemius muscle at neutral and 10° joint dorsiflexion was higher in males compared to females (p<0.05); however, the stiffness value of difference between neutral and 10° joint dorsiflexion for the Achilles tendon and gastrocnemius muscle was similar in both groups (p>0.05).

DISCUSSION

The obtained results suggest that MyotonPRO is a reliable and repeatable device in measuring the stiffness of the Achilles tendon and gastrocnemius muscle. Furthermore, males have stiffer Achilles tendon and gastrocnemius muscle, compared to females; however, the change in the stiffness of the assessed tissues caused by joint motion was similar in both sexes.

Tendons from kangaroo rats are exceptionally strong and tough

Tendons must be able to withstand the forces generated by muscles and not fail. Accordingly, a previous comparative analysis across species has shown that tendon strength (i.e., failure stress) increases for larger species. In addition, the elastic modulus increases proportionally to the strength, demonstrating that the two properties co-vary. However, some species may need specially adapted tendons to support high performance motor activities, such as sprinting and jumping. Our objective was to determine if the tendons of kangaroo rats (k-rat), small bipedal animals that can jump as high as ten times their hip height, are an exception to the linear relationship between elastic modulus and strength. We measured and compared the material properties of tendons from k-rat ankle extensor muscles to those of similarly sized white rats. The elastic moduli of k-rat and rat tendons were not different, but k-rat tendon failure stresses were much larger than the rat values (nearly 2 times larger), as were toughness (over 2.5 times larger) and ultimate strain (over 1.5 times longer). These results support the hypothesis that the tendons from k-rats are specially adapted for high motor performance, and k-rat tendon could be a novel model for improving tissue engineered tendon replacements.

An 8-week resistance training protocol is effective in adapting quadriceps but not patellar tendon shear modulus measured by Shear Wave Elastography

Habitual loading and resistance training (RT) can lead to changes in muscle and tendon morphology as well as in its mechanical properties which can be measured by Shear Wave Elastography (SWE) technique. The objective of this study was to analyze the Vastus Lateralis (VL) and patellar tendon (PT) mechanical properties adaptations to an 8-week RT protocol using SWE. We submitted 15 untrained health young men to an 8-week RT directed for knee extensor mechanism. VL and PT shear modulus (μ) were assessed pre and post intervention with SWE. PT thickness (PTT), VL muscle thickness (VL MT) and knee extension torque (KT) were also measure pre and post intervention to ensure the RT efficiency. Significant increases were observed in VL MT and KT (pre = 2.40 ± 0.40 cm and post = 2.63 ± 0.35 cm, p = 0.0111, and pre = 294.66 ± 73.98 Nm and post = 338.93 ± 76.39 Nm, p = 0.005, respectively). The 8-week RT was also effective in promoting VL μ adaptations (pre = 4.87 ± 1.38 kPa and post = 9.08.12 ± 1.86 kPa, p = 0.0105), but not in significantly affecting PT μ (pre = 78.85 ± 7.37 kPa and post = 66.41 ± 7.25 kPa, p = 0.1287) nor PTT (baseline = 0.364 ± 0.053 cm and post = 0.368 ± 0.046 cm, p = 0.71). The present study showed that an 8-week resistance training protocol was effective in adapting VL μ but not PT μ. Further investigation should be conducted with special attention to longer interventions, to possible PT differential individual responsiveness and to the muscle-tendon resting state tension environment.

Sex Differences in Mechanical Properties of the Achilles Tendon: Longitudinal Response to Repetitive Loading Exercise

Lepley, AS, Joseph, MF, Daigle, NR, Digiacomo, JE, Galer, J, Rock, E, Rosier, SB, and Sureja, PB. Sex differences in mechanical properties of the Achilles tendon: Longitudinal response to repetitive loading exercise. J Strength Cond Res 32(11): 3070-3079, 2018-Sex differences have been observed in the mechanical properties of the Achilles tendon, which may help to explain the increased risk of injury in men. However, the response and recovery of tendon mechanics to repetitive loading exercise, as well as sex-dependent responses, are not well understood. The purpose of our study was to compare Achilles tendon mechanical properties between men and women before, immediately after, and 60 minutes after a repetitive loading exercise. Seventeen female (age: 24.0 ± 3.9 years; height: 167.4 ± 6.9 cm; and mass: 64.9 ± 8.5 kg) and 18 male (age: 23.9 ± 2.4 years; height: 179.2 ± 5.09 cm; and mass: 78.4 ± 8.7 kg) recreationally active individuals volunteered. Using isokinetic dynamometry and diagnostic ultrasound, baseline levels of Achilles tendon force, elongation, stiffness, stress, strain, and Young's modulus were assessed before 100 successive calf-raise exercises using a Smith machine at 20% of participant body mass. Outcomes were reassessed immediately and 60 minutes after exercise. Women exhibited less Achilles tendon force, stiffness, stress, and modulus compared with men, regardless of time point. Both sexes responded to repetitive loading exercise similarly, with immediate decreases in mechanical properties of the Achilles tendon from baseline to immediately after exercise. Tendon properties were observed to be equal to baseline values at 60-minute postexercise. Baseline differences in tendon properties may help to explain the disparity in injury risk because both sexes responded to and recovered from exercise similarly. Future research should aim to include additional time points (both leading up to and after 60 minutes), and assess tendon responses to more sport-specific activities, while also including patients diagnosed with Achilles tendon injuries.

Load magnitude affects patellar tendon mechanical properties but not collagen or collagen cross-linking after long-term strength training in older adults

BACKGROUND

Regular loading of tendons may counteract the negative effects of aging. However, the influence of strength training loading magnitude on tendon mechanical properties and its relation to matrix collagen content and collagen cross-linking is sparsely described in older adults. The purpose of the present study was to compare the effects of moderate or high load resistance training on tendon matrix and its mechanical properties.

METHODS

Seventeen women and 19 men, age 62-70 years, were recruited and randomly allocated to 12 months of heavy load resistance training (HRT), moderate load resistance training (MRT) or control (CON). Pre- and post-intervention testing comprised isometric quadriceps strength test (IsoMVC), ultrasound based testing of in vivo patellar tendon (PT) mechanical properties, MRI-based measurement of PT cross-sectional area (CSA), PT biopsies for assessment of fibril morphology, collagen content, enzymatic cross-links, and tendon fluorescence as a measure of advanced glycation end-products (AGEs).

RESULTS

Thirty three participants completed the intervention and were included in the data analysis. IsoMVC increased more after HRT (+ 21%) than MRT (+ 8%) and CON (+ 7%) (p < 0.05). Tendon stiffness (p < 0.05) and Young's modulus (p = 0.05) were also differently affected by training load with a reduction in CON and MRT but not in HRT. PT-CSA increased equally after both MRT and HRT. Collagen content, fibril morphology, enzymatic cross-links, and tendon fluorescence were unaffected by training.

CONCLUSION

Despite equal improvements in tendon size after moderate and heavy load resistance training, only heavy. load training seemed to maintain tendon mechanical properties in old age. The effect of load magnitude on tendon biomechanics was unrelated to changes of major load bearing matrix components in the tendon core. The study is a sub-study of the LISA study, which was registered at http://clinicaltrials.gov (NCT02123641) April 25th 2014.

Effect of Gender on Mechanical Properties of the Plantar Fascia and Heel Fat Pad

BACKGROUND

The purpose of the study was to investigate the plantar fascia and heel fat pad stiffness and thickness parameters in females and compare these values with those of males.

METHODS

This study was carried out in 60 healthy sedentary participants (30 female, 30 male) between the ages of 19 and 50 years. Shear wave velocity (SWV) and thickness of the plantar fascia and heel fat pad were measured with an ultrasonography device.

RESULTS

Males had a higher plantar fascia ( P = .037) and heel fat pad ( P = .001) thickness compared with females, but SWV of the plantar fascia ( P = .673), heel fat pad microchamber layer ( P = .240), and heel fat pad macrochamber layer ( P = .636) were similar in both groups. Body mass had a strong correlation with the plantar fascia ( r = 0.64, P < .001) and heel fat pad thickness ( r = 0.68, P < .001). Height had a moderate correlation with the plantar fascia ( r = 0.44, P < .001) and heel fat pad thickness ( r = 0.42, P = .001).

CONCLUSION

Plantar fascia and heel fat pad stiffness were similar in both genders; however, females had a lower plantar fascia and heel fat pad thickness compared with males. Correlation analysis results suggest that higher plantar fascia and heel fat pad thickness in males may be related to higher body mass and height.

LEVELS OF EVIDENCE

Level III: Retrospective comparative study.

Ultrasound elastography of the patellar tendon in young, asymptomatic sedentary and moderately active individuals

BACKGROUND

The recent use of ultrasound elastography to study patellar tendon softness has demonstrated increased tendon softness in high-level athletes. We hypothesized that measurable alterations in patellar tendon softness may be present in young asymptomatic subjects engaging in moderate levels of physical activity.

METHODS

This was a cross-sectional study. Gray-scale ultrasound and ultrasound elastography of the right and left patellar tendons were performed in young asymptomatic sedentary subjects and moderately active subjects who engaged in at least 30 min of physical activity 4-5 times weekly. The distribution of soft, intermediate and stiff tissue within each tendon was analyzed. Tendon softness was correlated with subject age, gender and level of athletic activity.

RESULTS

Sixty patellar tendons in 30 subjects were evaluated (18 males, 12 females, mean age 22.5 years). Seventeen subjects were defined as "active" and 13 as "sedentary." All tendons had a normal gray-scale sonographic appearance. Tendon softness was significantly higher in active subjects (P = 0.01) and decreased with age (P = 0.04). In sedentary individuals there was no significant correlation between age and tendon softness (P = 0.404). Similarly, gender showed no correlation with tendon softness (P > 0.05).

CONCLUSIONS

Patellar tendon softness is higher in young subjects and in those engaging in moderate physical activity. This may reflect an adaptation to increased tendon load. Tendon softness in active subjects decreases with age, while it remains at a constant value in sedentary individuals.

LEVEL OF EVIDENCE

Level 3.

Lower tendon stiffness in very old compared with old individuals is unaffected by short-term resistance training of skeletal muscle

Aging negatively affects collagen-rich tissue, like tendons, but in vivo tendon mechanical properties and the influence of physical activity after the 8th decade of life remain to be determined. This study aimed to compare in vivo patellar tendon mechanical properties in moderately old (old) and very old adults and the effect of short-term resistance training. Twenty old (9 women, 11 men, >65 yr) and 30 very old (11 women, 19 men, >83 yr) adults were randomly allocated to heavy resistance training (HRT) or no training (CON) and underwent testing of in vivo patellar tendon (PT) mechanical properties and PT dimensions before and after a 3-mo intervention. Previous measurements of muscle properties, blood parameters, and physical activity level were included in the analysis. Data from 9 old HRT, 10 old CON, 14 very old CON, and 12 old HRT adults were analyzed. In addition to lower quadriceps muscle strength and cross-sectional area (CSA), we found lower PT stiffness and Young's modulus ( P < 0.001) and a trend toward the lower mid-portion PT-CSA ( P = 0.09) in very old compared with old subjects. Daily step count was also lower in very old subjects ( P < 0.001). Resistance training improved muscle strength and cross-sectional area equally in old and very old subjects ( P < 0.05) but did not affect PT mechanical properties or dimension. We conclude that PT material properties are reduced in very old age, and this may likely be explained by reduced physical activity. Three months of resistance training however, could not alter PT mechanical properties in very old individuals. NEW & NOTEWORTHY This research is the first to quantify in vivo tendon mechanical properties in a group of very old adults in their eighties. Patellar tendon stiffness was lower in very old (87 yr on average) compared with moderately old (68 yr on average) individuals. Reduced physical activity with aging may explain some of the loss in tendon stiffness, but regular heavy resistance training for 3 mo was not sufficient to change tendon mechanical properties.

Nonuniform Deformation of the Patellar Tendon During Passive Knee Flexion

The purpose of this study was to evaluate localized patterns of patellar tendon deformation during passive knee flexion. Ultrasound radiofrequency data were collected from the patellar tendons of 20 healthy young adults during knee flexion over a range of motion of 50°-90° of flexion. A speckle tracking approach was used to compute proximal and distal tendon displacements and elongations. Nonuniform tissue displacements were visible in the proximal tendon (P < .001), with the deep tendon undergoing more distal displacement than the superficial tendon. In the distal tendon, more uniform tendon motion was observed. Spatial variations in percent elongation were also observed, but these varied along the length of the tendon (P < .002), with the proximal tendon remaining fairly isometric while the distal tendon underwent slight elongation. These results suggest that even during passive flexion the tendon undergoes complex patterns of deformation. Proximal tendon nonuniformity may arise from its complex anatomy where the deep tendon inserts onto the patella and the superficial tendon extends to the quadriceps tendon. Such heterogeneity is not captured in whole tendon average assessments, emphasizing the relevance of considering localized tendon mechanics, which may be key to understanding tendon behavior and precursors to injury and disease.

The Association Between Fall History and Physical Performance Tests in the Community-Dwelling Elderly: A Cross-Sectional Analysis

Objective

To evaluate the association between baseline characteristics, three physical performance tests and fall history in a sample of the elderly from Korean population.

Methods

A total of 307 participants (mean age, 76.70±4.85 years) were categorized into one of two groups, i.e., fallers and non-fallers. Fifty-two participants who had reported falling unexpectedly at least once in the previous 12 months were assigned to the fallers group. Physical performance tests included Short Physical Performance Battery (SPPB), Berg Balance Scale (BBS), Timed Up and Go test. The differences between the two study groups were compared and we analyzed the correlations between fall histories and physical performance tests.

Results

SPPB demonstrated a significant association with fall history. Although the BBS total scores did not show statistical significance, two dynamic balance test items of BBS (B12 and B13) showed a significant association among fallers.

Conclusion

This study suggests that SPPB and two dynamic balance test items of the BBS can be used in screening for risk of falls in an ambulatory elderly population.

Patellar tendon mechanical properties change with gender, body mass index and quadriceps femoris muscle strength

OBJECTIVE

The purpose of this study is to assess the effect and correlation of gender, body mass index (BMI) and quadriceps femoris (QF) muscle strength on patellar tendon (PT) thickness and stiffness in healthy sedentary individuals.

METHODS

This study was carried out with 67 (36 female, 31 male) healthy sedentary individuals between the ages of 18-44 (28.0 ± 7.5 years). The individuals included in the study were divided into two groups according to their gender and BMI (18.5<BMI<25 and 25<BMI). The body composition was determined with Tanita Body Composition Analyser. PT thickness and stiffness was measured with ACUSON S3000 Ultrasonography Device using 9L4 ultrasonography probe. QF concentric muscle strength of the individuals was measured with Biodex^® System 4 Dynamometer at 60°/sec angular speed.

RESULTS

It was found that PT stiffness was higher in males compared to females (p<0.001). It was found that PT stiffness was lower in obese individuals compared to individuals with normal weight (p = 0.017). A negative and weak correlation was found between BMI and PT stiffness (r = -0.26, p = 0.032), whereas a negative and moderate correlation was found between fat percentage and PT stiffness (r = -0.50, p<0.001). A moderate correlation was found between BMI and PT thickness (r = 0.54, p<0.001). It was found that peak torque at 60°/sec angular speed had a moderate correlation with PT stiffness (r = 0.44, p<0.001) and PT thickness (r = 0.45, p<0.001).

CONCLUSIONS

PT stiffness is correlated and affected by gender, BMI and QF muscle strength whereas PT thickness is correlated and affected only to BMI and QF muscle strength.

Sex Hormones and Tendon

The risk of overuse and traumatic tendon and ligament injuries differ between women and men. Part of this gender difference in injury risk is probably explained by sex hormonal differences which are specifically distinct during the sexual maturation in the teenage years and during young adulthood. The effects of the separate sex hormones are not fully elucidated. However, in women, the presence of estrogen in contrast to very low estrogen levels may be beneficial during regular loading of the tissue or during recovering after an injury, as estrogen can enhance tendon collagen synthesis rate. Yet, in active young female athletes, physiological high concentration of estrogen may enhance the risk of injuries due to reduced fibrillar crosslinking and enhanced joint laxity. In men, testosterone can enhance tendon stiffness due to an enhanced tendon collagen turnover and collagen content, but testosterone has also been linked to a reduced responsiveness to relaxin. The present chapter will focus on sex difference in tendon injury risk, tendon morphology and tendon collagen turnover, but also on the specific effects of estrogen and androgens.

Structural and mechanical properties of the human Achilles tendon: Sex and strength effects

Tendons are elastic structures that connect muscle to the skeletal system and transmit force relative to the amount of stretch they experience. The mechanical properties of human tendons are difficult to measure non-invasively, so generic values are often assumed in musculoskeletal models to represent all subjects. We aimed to determine the in vivo mechanical properties of the human Achilles tendon by calculating tendon stiffness and resting length in 10 male and 10 female trained cyclists. B-mode ultrasound coupled with motion capture was used to track the tendon lengths for the medial and lateral gastrocnemii concurrently with ankle torque measurements during ramped isometric contractions. Achilles tendon stiffness was calculated as the slope of the linear portion of the force-length curve, and this was extrapolated to zero force to yield the tendon resting length. Average Achilles tendon stiffness was 201.8 ± 5.9 N mm(-1). There was no difference in Achilles tendon stiffness or maximum isometric force between males and females, however tendon stiffness varied between individuals. The resting lengths of the MG and LG tendon were 0.209 ± 0.002 m and 0.222 ± 0.002 m respectively, and regression models determined that shank length was the best predictor of resting tendon length. Our results indicate that Achilles tendon stiffness varies with muscle strength and not sex. The variability in Achilles tendon stiffness between subjects support the need for experimentally measured subject-specific tendon properties as input parameters to improve the accuracy of musculoskeletal models.

Region-specific tendon properties and patellar tendinopathy: a wider understanding

Patellar tendinopathy is a common painful musculoskeletal disorder with a very high prevalence in the athletic population that can severely limit or even end an athletic career. To date, the underlying pathophysiology leading to the condition remains poorly understood, although reports suggesting that patellar tendinopathy most frequently concerns the proximal posterior region of the tendon has prompted some researchers to examine region-specific tendon properties for a better understanding of the etiology and potential risk factors associated with the condition. However, to date, research concerning the in vivo region-specific tendon properties in relation to patellar tendinopathy is very scarce, perhaps due to the lack of validated techniques that can determine such properties in vivo. In recent years, a technique has been developed involving an automated tendon-tracking program that appears to be very useful in the determination of region-specific tendon properties in vivo. In terms of regional variations in tendon properties, previous research has demonstrated differences in structural, mechanical, and biochemical properties between the discrete regions of the patellar tendon, but the extent to which these regional variations contribute to patellar tendinopathy remains elusive. In addition, with respect to treatment strategies for patellar tendinopathy, previous research has utilized a wide range of interventions, but the use of eccentric exercise (EE) and/or heavy-slow resistance (HSR) training appear to be most promising. However, the optimal program design variables of EE and HSR training that induce the most favorable effects are yet to be determined. This review article provides a detailed discussion of all of the above to allow a better understanding of the etiology and potential risk factors associated with the condition as well as the most effective treatment strategies. First, a comprehensive literature review is provided with respect to region-specific structural, mechanical, and biochemical properties, in association with patellar tendinopathy. Second, the automated tendon-tracking methodology is outlined to assist future researchers in the determination of region-specific tendon properties. Finally, potential treatment strategies are discussed, particularly with regards to the use of EE and HSR training for the management of patellar tendinopathy.

Men older than 50 yrs are more likely to fall than women under similar conditions of health, body composition, and balance

OBJECTIVE

The aim of this study was to analyze the contribution of sex to the occurrence of falls, accounting for comorbidities and differences in physical fitness.

DESIGN

This was a cross-sectional study of 587 community-dwelling adults who were older than 50 yrs. Falls, comorbidities (number of diseases and physical impairments), and physical fitness (body composition, lower and upper body strength and flexibility, agility, aerobic endurance, and balance) were evaluated via questionnaires, bioimpedance, and Fullerton batteries, respectively.

RESULTS

Compared with the men, the women presented a 10% higher fall prevalence, 1.7 more diseases/impairments, 10% more body fat, 26% less lean body mass, and poorer physical capacity (P < 0.05). Multivariate logistic regression revealed that male sex (odds ratio [OR], 2.723; 95% confidence interval [CI], 1.190-6.230) increased the likelihood of falling, after adjustment for comorbidities (OR, 1.213; 95% CI, 1.109-1.328), lean mass (OR, 0.958; 95% CI, 0.927-0.989), fat mass (OR, 1.053; 95% CI, 1.021-1.086), and balance (OR, 0.942; 95% CI, 0.914-0.971), which were the main risk factors of falls.

CONCLUSIONS

Women are more susceptible to falling, presumably because they have poorer health and physical fitness than do men. However, when the values for comorbidities, lean and fat body mass, and balance were similar, the men demonstrated a higher probability of falling. Age is not a significant risk factor of falls under favorable conditions of health, body composition, and balance.

Subject-specific tendon-aponeurosis definition in Hill-type model predicts higher muscle forces in dynamic tasks

Neuromusculoskeletal models are a common method to estimate muscle forces. Developing accurate neuromusculoskeletal models is a challenging task due to the complexity of the system and large inter-subject variability. The estimation of muscles force is based on the mechanical properties of tendon-aponeurosis complex. Most neuromusculoskeletal models use a generic definition of the tendon-aponeurosis complex based on in vitro test, perhaps limiting their validity. Ultrasonography allows subject-specific estimates of the tendon-aponeurosis complex’s mechanical properties. The aim of this study was to investigate the influence of subject-specific mechanical properties of the tendon-aponeurosis complex on a neuromusculoskeletal model of the ankle joint. Seven subjects performed isometric contractions from which the tendon-aponeurosis force-strain relationship was estimated. Hopping and running tasks were performed and muscle forces were estimated using subject-specific tendon-aponeurosis and generic tendon properties. Two ultrasound probes positioned over the muscle-tendon junction and the mid-belly were combined with motion capture to estimate the in vivo tendon and aponeurosis strain of the medial head of gastrocnemius muscle. The tendon-aponeurosis force-strain relationship was scaled for the other ankle muscles based on tendon and aponeurosis length of each muscle measured by ultrasonography. The EMG-driven model was calibrated twice - using the generic tendon definition and a subject-specific tendon-aponeurosis force-strain definition. The use of subject-specific tendon-aponeurosis definition leads to a higher muscle force estimate for the soleus muscle and the plantar-flexor group, and to a better model prediction of the ankle joint moment compared to the model estimate which used a generic definition. Furthermore, the subject-specific tendon-aponeurosis definition leads to a decoupling behaviour between the muscle fibre and muscle-tendon unit in agreement with previous experiments using ultrasonography. These results indicate the use of subject-specific tendon-aponeurosis definitions in a neuromusculoskeletal model produce better agreement with measured external loads and more physiological model behaviour.

Gender differences in both active and passive parts of the plantar flexors series elastic component stiffness and geometrical parameters of the muscle-tendon complex

Men are reportedly at higher risk of plantar flexor muscle injury and Achilles tendon ruptures than women. Biomechanical parameters are thought to play a role in the higher frequency of injury to males. One parameter is the stiffness of tissues; a stiff tissue cannot absorb sufficient energy with loading, and subsequently may be more likely to be injured. Thus, our purpose was to investigate the gender difference in the geometrical parameters of plantar flexor's muscle-tendon complex and the stiffness of both active and passive parts of the series elastic component (S(SEC1) and S(SEC2) , respectively). Using the alpha method on data obtained from quick stretches to the plantar flexors performed during isometric contractions, S(SEC1) and S(SEC2) were assessed. Plantar flexor muscles and Achilles tendon cross-sectional areas (CSA(TS) and CSA(AT) , respectively) were determined in young healthy men (n = 49) and women (n = 31). The findings showed that S(SEC2) was higher in men (p < 0.001), but this difference was not apparent when S(SEC2) was normalized to CSA(AT) (p > 0.05). In contrast, S(SEC1) was lower in men (p < 0.001) and remained so after normalization to CSA(TS) . Higher joint stiffness observed in men was notably influenced by lever arm length. Thus, the results of this study have implications for performance and injury.

The magnitude and character of resistance-training-induced increase in tendon stiffness at old age is gender specific

Human tendon mechanical properties are modified with loading. Moreover, there are indications that the training response in the tendon is gender specific. The aim of the current study was to examine whether in vivo patella tendon stiffness (K) differentially alters with training in older males compared with females. We also aimed to identify which endocrine pathway underlies the responses. Maximal knee extensor forces were also monitored to determine the training effect on muscle function. Fourteen healthy, habitually active older persons (seven males aged 74.0 ± 1.2 years (mean±SEM) and seven females aged 76.7 ± 1.2 years) were tested at baseline and after 12 weeks of weekly, progressive resistance training. With training, percentage increase in quadriceps maximum voluntary isometric force (MVC) was similar in males (2,469.6 ± 168.0 to 3,097.3 ± 261.9 N; +25.3 ± 6.1% (p < 0.01)) and females (1,728.8 ± 136.3 to 2,166.5 ± 135.8 N; +30.4 ± 15.1% (p < 0.05)), respectively. K increased more in males (338.0 ± 26.6 to 616.9 ± 58.7 N/mm; 79.8 ± 4.2% (p < 0.001)) compared to females (338.9 ± 31.0 to 373.2 ± 25.8 N/mm; +13.0 ± 3.7% (p < 0.001)). Interestingly, a pattern was found whereby below ~40% MVC, the females showed their greatest degree of K changes, whereas the males showed their greatest degree of K change above this relative force level. This gender contrast was also true at a standardised force level (1,200 N), with 5.8 ± 0.4% vs. 82.5 ± 1.8% increments in the females (i.e. value change from 380.3 ± 14.1 to 402.4 ± 13.3 N/mm) and the males (i.e. value change from 317.8 ± 13.8 to 580.2 ± 30.9 N/mm), respectively (p < 0.001). While circulating levels of both IGF-I and IL-6 did not alter with training, IGFBP-3 showed a significant training effect (19.1 ± 4.8%, p < 0.001) and only in the male sub-group (p = 0.038). We show here that with training, in vivo older females' tendon is less dramatically modulated than that of males'. We also show that the relative forces, at which the greatest adaptations are exhibited, differ by gender, with a suggestion of endocrine adaptations in males only. We thus propose that both training and rehabilitation regimens should consider gender-specific tendon responsiveness, at least in older persons.

Computation methods affect the reported values of in vivo human tendon stiffness

PURPOSE

Scientific validity is questionable when findings from studies cannot be used to make sense of physiological and/or biomechanical data. In particular, is the case of in vivo determination of tendon stiffness (K). Here, approaches range from taking the gradient (a) throughout the data range of resting to Maximal Voluntary Contraction (MVC), (b) tangents at individual data points, (c) linear regressions at discrete force levels ((b) and (c) being 'reference standard' as they utilise a number of distinct regions of the Force-Elongation Relationship (FER)).

STUDY DESIGN

A mathematical model approach is used to develop simple curvilinear FERs as seen when determining tendon mechanical properties, to allow variable calculations of K.

OBJECTIVES

To compare variability in K estimates using the various approaches currently seen in the literature.

METHODS

Three FER models were developed, representing low, medium and high K. Values of K were determined and compared using the approaches reported in the literature to estimate the magnitude of the difference between values attained of K.

RESULTS

Through mathematical modelling, we demonstrate that the impact on the recorded value of K is substantial: relative to the reference standard methods, computation methods published range from underestimating K by 26% to overestimating it by 51%.

CONCLUSION

This modelling helps by providing a 'scaling factor' through which the between studies variability associated with computational methods differences is minimised. This is especially important where researchers or clinicians require values which are consistent in the context of establishing the 'true' tendon mechanical properties to inform models or materials based on the biological properties of the human tendon.

Effect of gender, age, fatigue and contraction level on electromechanical delay

OBJECTIVE

The aim of this study was to determine electromechanical delay (EMD) using supramaximal stimuli and to investigate its variation with gender, age, contraction level and fatigue.

METHODS

Fifteen male and 15 female healthy subjects (aged between 18 and 60) participated in our study. Electromyogram (EMG) recordings were taken from triceps surae muscle. While subjects contracted their muscles voluntarily at specified percentages of maximum voluntary contraction, 10 supramaximal stimuli were applied to the tibial nerve. The time lag between the onset of the EMG response (M-wave) and the onset of force generation was calculated as EMD.

RESULTS

EMD was found to be 8.5+/-1.3 ms (at rest condition), which is much shorter than those reported in previous studies. Although EMD did not significantly vary with gender (P>0.05), it decreased significantly with escalating muscle contraction level (P<0.05) and increased significantly with advancing age and with fatigue (P<0.05).

CONCLUSIONS

EMD was found to be considerably shorter than those reported in previous studies, and hence we discuss the possible reasons underlying this difference. We suggest that supramaximal nerve stimulation and high resolution EMG and force recording may have generated this difference.

SIGNIFICANCE

Current findings suggest that EMD is very sensitive to the method used to determine it. We discuss the reasons for the short EMD value that we have found in the present study.