Achilles tendon stiffness is unchanged one hour after a marathon

Influence of preconditioning on morphological and mechanical properties of human Achilles tendon in vivo

The present study aimed 1) to verify whether the effect of preconditioning was observed in the measured variables during the measurement of the human tendon in vivo (i.e., repeated contractions with breaks between trials) and 2) to determine the changes in tendon properties and their mechanisms due to submaximal repetitive contractions. Twelve healthy males participated in this study. To eliminate the effects of preconditioning, the participants rested on the measurement bed for 2 h before the start of both experiment-1 and experiment-2. In experiment-1, the measurements of elongation and hysteresis of the Achilles tendon for ramp and ballistic conditions were repeated ten times every 2 min. In experiment-2, participants performed submaximal repetitive contractions at 50 % of MVC and a frequency of 1 Hz for 10 min with a 30 s break every 2 min. Tendon mechanical properties were measured during contractions (starting 30 s and last 20 s of every 2 min), and the mean and coefficient variation (CV) of echogenicity were assessed during a 30-s rest every 2 min. In experiment-1, no significant differences in elongation and hysteresis of the tendon for ramp and ballistic contractions were found among the trials. In experiment 2, there were no significant differences in tendon elongation and hysteresis among all measurement times. Mean echogenicity increased significantly after 2 min, and CV of echogenicity decreased significantly after 4 min. These results suggest that preconditioning does not affect the elongation and hysteresis of the Achilles tendon in measuring tendon mechanical properties and submaximal repetitive contractions.

Effect of gender and running experience on lower limb biomechanics following 5 km barefoot running

Barefoot running has been increasing in popularity, yet there is a gap in understanding concerning the biomechanics of mid-distance barefoot running, especially between genders and runners of different running-experience levels. This study examines the effects of running-experience, gender, and their interaction on running biomechanics following 5 km barefoot running. Before and after a 5 km run, three-dimensional kinematics and kinetics of the lower limb joints and plantar pressure during barefoot running were collected from 20 participants. Participants were stratified by their running-experience levels (novice and marathon-experienced) and gender. This study revealed significant gender effects on lower limb biomechanics following a 5 km barefoot run. Increased plantar pressure under the lateral aspect of the foot was observed in the female cohort, while the male cohort exhibited reduced plantar pressure under the lateral heel. This study suggests that modified lower limb running biomechanics and modified lateral foot loading after 5 km barefoot running may create a different foot loading environment for female and male runners that should be accommodated in barefoot runningand minimalist shoe design.

Modelling and in vivo evaluation of tendon forces and strain in dynamic rehabilitation exercises: a scoping review

OBJECTIVES

Although exercise is considered the preferred approach for tendinopathies, the actual load that acts on the tendon in loading programmes is usually unknown. The objective of this study was to review the techniques that have been applied in vivo to estimate the forces and strain that act on the human tendon in dynamic exercises used during rehabilitation.

DESIGN

Scoping review.

DATA SOURCES

Embase, PubMed, Web of Science and Google Scholar were searched from database inception to February 2021.

ELIGIBILITY CRITERIA

Cross-sectional studies available in English or Spanish language were included if they focused on evaluating the forces or strain of human tendons in vivo during dynamic exercises. Studies were excluded if they did not evaluate tendon forces or strain; if they evaluated running, walking, jumping, landing or no dynamic exercise at all; and if they were conference proceedings or book chapters.

DATA EXTRACTION AND SYNTHESIS

Data extracted included year of publication, study setting, study population characteristics, technique used and exercises evaluated. The studies were grouped by the types of techniques and the tendon location.

RESULTS

Twenty-one studies were included. Fourteen studies used an indirect methodology based on inverse dynamics, nine of them in the Achilles and five in the patellar tendon. Six studies implemented force transducers for measuring tendon forces in open carpal tunnel release surgery patients. One study applied an optic fibre technique to detect forces in the patellar tendon. Four studies measured strain using ultrasound-based techniques.

CONCLUSIONS

There is a predominant use of inverse dynamics, but force transducers, optic fibre and estimations from strain data are also used. Although these tools may be used to make general estimates of tendon forces and strains, the invasiveness of some methods and the loss of immediacy of others make it difficult to provide immediate feedback to the individuals.

Effect of training volume on footstrike patterns over an exhaustive run

BACKGROUND

Although footstrike pattern (FP) may not be a factor influencing running performance, 11-75% of world-class distance runners use a non-rearfoot FP. However, little attention has been paid to describe the effect of running volume on FP changes when a runner is fatigued.

RESEARCH QUESTION

Does the training volume provide an adequate stimulus to mitigate FP changes during an exhaustive run in non-rearfoot, habitual minimalist footwear runners?

METHODS

The objective of this study was to compare FP between non-rearfoot, habitual minimalist footwear runners with a moderate training volume (MT) and a high training volume (HT) during an exhaustive run on a motorized treadmill. Based on their weekly training volume (distance), twenty-eight runners were arranged into two groups paired by height and age. At the first visit, runners underwent a VO2max test to acquire their velocity for the exhaustive run. During the second visit, biomechanical and physiological analysis of the beginning and the end phase of the exhaustive run was done.

RESULTS

The frontal plane foot angle, the sagittal plane ankle angle at the initial contact (IC), and the foot eversion ROM showed a significant interaction effect (P < 0.05). Additionally, the sagittal plane footstrike angle, the frontal plane foot angle, the sagittal plane ankle angle, knee flexion angle at IC and foot eversion ROM showed a significant effect of fatigue (P < 0.05). Finally, the frontal plane foot angle, the sagittal plane footstrike angle, the sagittal plane ankle angle, and the knee flexion angle showed significant group effects (P < 0.05).

SIGNIFICANCE

The training volume affects the footstrike pattern of non-rearfoot, habitual minimalist footwear runners when they are fatigued. The highly trained runners maintained their ankle angle throughout the exhaustive running protocol, whereas the moderately trained group changed the frontal and sagittal plane characteristics of their footstrike pattern.

Ultrasound evaluation of the patellar tendon and Achilles tendon and its association with future pain in distance runners

Objectives: To examine whether asymptomatic ultrasonographic abnormalities in the Achilles and patellar tendons in runners are associated with an increased risk of pain development.Methods: This is a longitudinal, prospective cohort study with 139 runners recruited at a half and full marathon race. Ultrasound examination of the Achilles and patellar tendons was performed bilaterally the day prior to the race. Self-reported injury data were collected at 1, 3, 6 and 12 months. 104 (74.8%) runners were included in the data analysis.Results: Ultrasonographic tendon abnormalities were found in 24.1% of the Achilles and in 23.1% of the patellar tendons prior to the race. Runners with tendon abnormality were 2-3 times more likely to develop pain within 12 months than those without (relative risk = 3.14, p = 0.010 for Achilles; relative risk = 2.52, p = 0.008 for patellar tendon). After adjusting for gender, age, years of running, average miles per week of running over a year, and pre-race pain, runners with ultrasound abnormality were about 3 times (hazard ratio = 2.89, p = 0.039 for Achilles; hazard ratio = 2.73, p = 0.030 for patellar tendon) more likely to develop pain after the race. Tendon delamination was most strongly associated with pain in both the Achilles (relative risk = 6.00; p = 0.001) and patellar tendons (relative risk = 3.81; p = 0.001).Conclusions: Structural changes in asymptomatic tendons were found in almost 25% of runners. Presence of structural changes was associated with increased development of Achilles and patellar tendon pain within one year.

Ankle joint rotation and exerted moment during plantarflexion dependents on measuring- and fixation method

We examined the effect of ankle joint fixation vs increased foot pressure (aiming to reduce dynamometer-subject elasticity (DSE)) on the exerted moment during plantarflexion contraction. We also examined the joint rotation in dependence of the measuring site (forefoot, rearfoot) and the foot condition (fixed, free). We hypothesized higher exerted moments due to reduced DSE compared to fixed condition and an effect of fixation on the joint rotation in dependence of the measuring site. Fourteen healthy individuals (28.7±6.9y) completed in randomized order maximal isometric plantarflexions in four different positions (0-3-6-9 cm) and two ankle joint conditions (fixed-free). Kinematics of the rear- and forefoot were obtained synchronously. We found higher moment in the fixed compared to the free condition at all positions. The maximum moment in the fixed condition did not differ at any position. At the fixed condition, the forefoot rotation did not differ at any position (~5°) while at free condition we observed a significant rotation reduction (form ~12 to ~5°). The rearfoot rotation did not differ between conditions at any position while a significant joint angle reduction was observed (~10 to ~6° and ~12 to ~6°; fixed-free respectively). The results indicate that with appropriate foot fixation the maximum moment can be achieved irrespective of the position. With the foot secured, the measuring site influences the rotational outcome. We suggest that for a minimization of the joint rotation a fixation and the forefoot-measuring site should be preferred. Additionally, for unconstrained foot kinematic observations both measuring sites can be obtained.

Muscle Recovery after a Single Bout of Functional Fitness Training

Background: Functional fitness training (FFT) is a new exercise modality that targets functional multi-joint actions via both muscle-strengthening exercises and aerobic training intervals. The aim of the study was to examine muscle recovery over a 20 min period after an FFT workout in trained adults. Materials and methods: Participants were 28 healthy trained subjects. In a single session, a countermovement jump (CMJ) was performed to determine several mechanical variables (jump height, maximum velocity, power) before (preFFT) and 4, 10, and 20 min after the FFT workout (postFFT). In parallel, capillary blood lactate concentrations were measured pre- and 3 min postFFT. Heart rate was also measured before and after the workout, and perceived exertion was measured postFFT. Results: Significant differences between the time points preFFT and 4 min and 10 min postFFT, respectively, were produced in jump height (p = 0.022, p = 0.034), maximum velocity (p = 0.016, p = 0.005), average power relative (p = 0.018, p = 0.049), and average power total (p = 0.025, p = 0.049). No differences were observed in any of the variables recorded preFFT and 20 min postFFT. Conclusions: While mechanical variables indicating muscle fatigue were reduced 4 and 10 min postFFT, pre-exercise jump ability only really started to recover 20 min after FFT although not reaching pre-exercise levels. This means that ideally intervals of around 20 min of rest should be implemented between training bouts.

The differences in viscoelastic properties of subtendons result from the anatomical tripartite structure of human Achilles tendon - ex vivo experimental study and modeling

The human Achilles tendon (AT) is a hierarchical structure macroscopically composed of three subtendons originating from the soleus (SOL) and gastrocnemius (GL, GM) muscles. According to recent reports, the divisible structure of the AT together with diverse material properties of its subtendons are suspected as a probable cause of non-homogeneous stress and strain distribution occurring in loaded AT. Despite numerous investigations on human AT, there is still relatively little knowledge regarding mechanical properties of subtendon-level hierarchy, which is crucial in fully understanding the multiscale relationship which governs tendon mechanics. In this paper we present the first ex vivo study conducted on SOL, GL, and GM subtendons of human AT. We investigate differences in viscoelastic properties of SOL, GM, and GL subtendons in terms of tensile modulus, mechanical hysteresis as well as stress relaxation observed at two different values of strain. Our results show that the most significant differences in mechanical properties exist between subtendon attached to the soleus muscle (SOL) and subtendons originating from the two heads of the gastrocnemius muscle (GM and GL). We used our experimental results to calibrate three different constitutive models: the hyperelastic Yeoh model with power-law flow, the microstructurally motivated Holzapfel-Gasser-Ogden model enhanced with strain-dependent Berström-Boyce flow and the phenomenological elasto-viscoplastic Arruda-Boyce-based model with strain-dependent Berström-Boyce flow supplemented with component representing matrix response. All calibrated models may be applied to commercial FEA software as a sufficient solution for rapid mechanical response modeling of human AT subtendons or for the purpose of future development of comprehensive patient-specific models of human lower limbs. STATEMENT OF SIGNIFICANCE: The divisible structure of the Achilles tendon together with diverse material properties of its subtendons are suspected as a probable cause of non-homogeneous stress and strain distribution occurring in loaded Achilles tendon. Despite numerous investigations on mechanical properties of Achilles tendon, there is still relatively little knowledge regarding mechanical properties of subtendon-level hierarchy, which is crucial in fully understanding the multiscale relationship which governs tendon mechanics. This study is the first reported ex vivo investigation conducted on SOL, GL, and GM human Achilles subtendons. We investigate differences in the viscoelastic properties of individual subtendons and demonstrate that the observed differences should be considered as muscle-dependent. Our experimental research is supported with a modeling study in which we calibrate three different constitutive models.

Disability, Physical Impairments, and Poor Quality of Life, Rather Than Radiographic Changes, Are Related to Symptoms in Individuals With Ankle Osteoarthritis: A Cross-sectional Laboratory Study

OBJECTIVE

To compare physical and patient-reported outcomes between (1) individuals with symptomatic radiographic ankle osteoarthritis (OA) and asymptomatic individuals, and (2) asymptomatic individuals with and without radiographic ankle OA.

DESIGN

Cross-sectional study.

METHODS

Ninety-six volunteers (31 symptomatic individuals with radiographic ankle OA, 41 asymptomatic individuals with radiographic ankle OA, and 24 asymptomatic individuals without radiographic ankle OA) completed a survey on quality of life (QoL), function, pain, disability, kinesiophobia, ankle instability, and physical activity, and undertook physical assessments of ankle muscle strength, heel-raise endurance, dorsiflexion range of motion (ROM), and ambulatory function.

RESULTS

Symptomatic individuals with radiographic ankle OA reported greater pain (standardized mean difference [SMD], 1.70; 95% confidence interval [CI]: 1.18, 2.23), disability (SMD, 1.44; 95% CI: 0.93, 1.95), and instability (SMD, -3.92; 95% CI: -4.68, -3.17), and lower patient-reported function (SMD, -2.10; 95% CI: -2.66, -1.54) and QoL (SMD, -0.98; 95% CI: -1.47, -0.50), than asymptomatic individuals. Muscle strength (all SMDs, -0.73 or greater), heel-raise endurance (SMD, -0.71; 95% CI: -1.16, -0.25), dorsiflexion ROM (SMD, -1.54; 95% CI: -2.02, -1.06), and ambulatory function (all SMDs, 0.57 or greater) were significantly impaired in symptomatic individuals with radiographic ankle OA compared to asymptomatic individuals. Most patient-reported and physical outcomes were similar between asymptomatic individuals with and without radiographic ankle OA.

CONCLUSION

Individuals with symptomatic radiographic ankle OA had poorer physical outcomes, function, and QoL compared to asymptomatic individuals with and without radiographic ankle OA. This suggests that disability in ankle OA is related to symptoms rather than to radiographic evidence of degeneration. J Orthop Sports Phys Ther 2020;50(12):711-722. doi:10.2519/jospt.2020.9376.

Techniques for In Vivo Measurement of Ligament and Tendon Strain: A Review

The critical clinical and scientific insights achieved through knowledge of in vivo musculoskeletal soft tissue strains has motivated the development of relevant measurement techniques. This review provides a comprehensive summary of the key findings, limitations, and clinical impacts of these techniques to quantify musculoskeletal soft tissue strains during dynamic movements. Current technologies generally leverage three techniques to quantify in vivo strain patterns, including implantable strain sensors, virtual fibre elongation, and ultrasound. (1) Implantable strain sensors enable direct measurements of tissue strains with high accuracy and minimal artefact, but are highly invasive and current designs are not clinically viable. (2) The virtual fibre elongation method tracks the relative displacement of tissue attachments to measure strains in both deep and superficial tissues. However, the associated imaging techniques often require exposure to radiation, limit the activities that can be performed, and only quantify bone-to-bone tissue strains. (3) Ultrasound methods enable safe and non-invasive imaging of soft tissue deformation. However, ultrasound can only image superficial tissues, and measurements are confounded by out-of-plane tissue motion. Finally, all in vivo strain measurement methods are limited in their ability to establish the slack length of musculoskeletal soft tissue structures. Despite the many challenges and limitations of these measurement techniques, knowledge of in vivo soft tissue strain has led to improved clinical treatments for many musculoskeletal pathologies including anterior cruciate ligament reconstruction, Achilles tendon repair, and total knee replacement. This review provides a comprehensive understanding of these measurement techniques and identifies the key features of in vivo strain measurement that can facilitate innovative personalized sports medicine treatment.

Changes in joint, muscle, and tendon stiffness following repeated hopping exercise

The purpose of this study was to elucidate the mechanisms of decline in joint stiffness after repeated stretch‐shortening cycle exercises according to changes in both muscle‐tendon properties and neuromuscular activities. Eleven males performed fatigue task (5 sets of 50 hopping). Ankle joint stiffness and electromyographic activities (mEMG) of plantar flexor and tibial anterior muscles during drop jump were measured before and after fatigue task. Active muscle stiffness with (100 deg·sec⁻¹) and without (250 deg·sec⁻¹) stretch reflex were calculated according to changes in estimated muscle force and fascicle length during fast stretching after submaximal isometric contractions. Tendon stiffness was measured during ramp and ballistic contractions. After fatigue task, joint stiffness significantly decreased by 20.7 %, whereas mEMG of measured muscles during drop jump did not. After fatigue task, active muscle stiffness with and without stretch reflex significantly decreased by 15.7 % and 21.5 %, and tendon stiffness measured during ramp and ballistic contractions did not change. In addition, the relative change in joint stiffness was significantly correlated with that in active muscle stiffness with stretch reflex (r = 0.737, P = 0.009), but not with those in the other measured variables. These results suggested that the decline in joint stiffness after repeated hopping exercises would be caused by changes in active muscle stiffness, but not those in tendon properties or neuromuscular activities.

Men's and Women's World Championship Marathon Performances and Changes With Fatigue Are Not Explained by Kinematic Differences Between Footstrike Patterns

World-class marathon runners make initial contact with the rearfoot, midfoot or forefoot. This novel study analyzed kinematic similarities and differences between rearfoot and non-rearfoot strikers within the men's and women's 2017 IAAF World Championship marathons across the last two laps. Twenty-eight men and 28 women, equally divided by footstrike pattern, were recorded at 29.5 and 40 km (laps 3 and 4, respectively) using two high-definition cameras (50 Hz). The videos were digitized to derive spatiotemporal and joint kinematic data, with additional footage (120 Hz) used to identify footstrike patterns. There was no difference in running speed, step length or cadence between rearfoot and non-rearfoot strikers during either lap in both races, and these three key variables decreased in athletes of either footstrike pattern to a similar extent between laps. Men slowed more than women between laps, and overall had greater reductions in step length and cadence. Rearfoot strikers landed with their foot farther in front of the center of mass (by 0.02-0.04 m), with non-rearfoot strikers relying more on flight distance for overall step length. Male rearfoot strikers had more extended knees, dorsiflexed ankles and hyperextended shoulders at initial contact than non-rearfoot strikers, whereas female rearfoot strikers had more flexed hips and extended knees at initial contact. Very few differences were found at midstance and toe-off. Rearfoot and non-rearfoot striking techniques were therefore mostly indistinguishable except at initial contact, and any differences that did occur were very small. The spatiotemporal variables that differed between footstrike patterns were not associated with faster running speeds and, ultimately, neither footstrike pattern prevented reductions in running speeds. The only joint angle measured at a specific gait event to change with fatigue was midswing knee flexion angle in men. Coaches should thus note that encouraging marathon runners to convert from rearfoot to non-rearfoot striking is unlikely to provide any performance benefits, and that training the fatigue resistance of key lower limb muscle-tendon units to avoid decreases in step length and cadence are more useful in preventing reductions in speed during the later stages of the race.

Mechanical and Material Tendon Properties in Patients With Proximal Patellar Tendinopathy

Introduction

The effect of chronic patellar tendinopathy on tissue function and integrity is currently unclear and underinvestigated. The aim of this cohort comparison was to examine morphological, material, and mechanical properties of the patellar tendon and to extend earlier findings by measuring the ability to store and return elastic energy in symptomatic tendons.

Methods

Seventeen patients with chronic (>3 months, VISA-P < 80), inferior pole patellar tendinopathy (24 ± 4 years; male = 12, female = 5) were carefully matched to controls (25 ± 3 years) for training status, pattern, and history of loading of the patellar tendon. Individual knee extension force, patellar tendon stiffness, stress, strain, Young’s modulus, hysteresis, and energy storage capacity, were obtained with combined dynamometry, ultrasonography, magnetic resonance imaging, and electromyography.

Results

Anthropometric parameters did not differ between groups. VISA-P scores ranged from 28 to 78 points, and symptoms had lasted from 10 to 120 months before testing. Tendon proximal cross-sectional area was 61% larger in the patellar tendinopathy group than in the control group. There were no differences between groups in maximal voluntary isometric knee extension torque (p = 0.216; d < −0.31) nor in tensile tendon force produced during isometric ramp contractions (p = 0.185; d < −0.34). Similarly, tendon strain (p = 0.634; d < 0.12), hysteresis (p = 0.461; d < 0.18), and strain energy storage (p = 0.656; d < 0.36) did not differ between groups. However, patellar tendon stiffness (−19%; p = 0.007; d < −0.74), stress (−27%; p< 0.002; d < −0.90) and Young’s modulus (−32%; p = 0.001; d < −0.94) were significantly lower in tendinopathic patients compared to healthy controls.

Discussion

In this study, we observed lower stiffness in affected tendons. However, despite the substantial structural and histological changes occurring with tendinopathy, the tendon capacity to store and dissipate energy did not differ significantly.

Running a Marathon-Its Influence on Achilles Tendon Structure

CONTEXT

Several studies have been conducted to better understand the effect of load on the Achilles tendon structure. However, the effect of a high cumulative load consisting of repetitive cyclic movements, such as those that occur during the running of a marathon, on Achilles tendon structure is not yet clear. Clinicians, coaches, and athletes will benefit from knowledge about the effects of a marathon on the structure of the Achilles tendon.

OBJECTIVE

To investigate the short-term response of the Achilles tendon structure to running a marathon.

DESIGN

Case series (prospective).

SETTING

Sports medicine centers.

PATIENTS OR OTHER PARTICIPANTS

Ten male nonelite runners who ran in a marathon.

MAIN OUTCOMES MEASURE(S)

Tendon structure was assessed before and 2 and 7 days after a marathon using ultrasound tissue characterization (UTC), an imaging tool that quantifies tendon organization in 4 echo types (I-IV). Echo type I represents the most stable echo pattern, and echo type IV, the least stable.

RESULTS

At 7 days postmarathon, both the insertional and midportion structure changed significantly. At both sites, the percentage of echo type II increased (insertion P < .01; midportion P = .02) and the percentages of echo types III and IV decreased (type III: insertion P = .01; midportion P = .02; type IV: insertion P = .01; midportion P < .01). Additionally, at the insertion, the percentage of echo type I decreased (P < .01).

CONCLUSIONS

We observed the effects of running a marathon on the Achilles tendon structure 7 days after the event. Running the marathon combined with the activity performed shortly thereafter might have caused the changes in tendon structure. This result emphasizes the importance of sufficient recovery time after running a marathon to prevent overuse injuries.

Medial Gastrocnemius Muscle Architecture Is Altered After Exhaustive Stretch-Shortening Cycle Exercise

Muscle architecture is an important component of muscle function, and recent studies have shown changes in muscle architecture with fatigue. The stretch-shortening cycle is a natural way to study human locomotion, but little is known about how muscle architecture is affected by this type of exercise. This study investigated potential changes in medial gastrocnemius (MG) muscle architecture after exhaustive stretch-shortening cycle exercise. Male athletes (n = 10) performed maximal voluntary contractions (MVC) and maximal drop jump (DJ) tests before and after an exercise task consisting of 100 maximal DJs followed by successive rebound jumping to 70% of the initial maximal height. The exercise task ceased upon failure to jump to 50% of maximal height or volitional fatigue. Muscle architecture of MG was measured using ultrasonography at rest and during MVC, and performance variables were calculated via a force plate and motion analysis. After SSC exercise, MVC (−13.1%; p = 0.005; d_z = 1.30), rebound jump height (−14.8%, p = 0.004; d_z = 1.32), and ankle joint stiffness (−26.3%; p = 0.008; d_z = 1.30) decreased. Ankle joint range of motion (+20.2%; p = 0.011; d_z = 1.09) and MG muscle-tendon unit length (+12.0%; p = 0.037; d_z = 0.91) during the braking phase of DJ, the immediate drop-off in impact force (termed peak force reduction) (Δ27.3%; p = 0.033; d_z = 0.86), and lactate (+9.5 mmol/L; p < 0.001; d_z = 3.58) increased. Fascicle length increased at rest (+4.9%; p = 0.013; d_z = 1.16) and during MVC (+6.8%; p = 0.048; d_z = 0.85). Pennation angle decreased at rest (−6.5%; p = 0.034, d_z = 0.93) and during MVC (−9.8%; p = 0.012; d_z = 1.35). No changes in muscle thickness were found at rest (−2.6%; p = 0.066; d_z = 0.77) or during MVC (−1.6%; p = 0.204; d_z = 0.49). The greater MG muscle-tendon stretch during the DJ braking phase after exercise indicates that muscle damage likely occurred. The lower peak force reduction and ankle joint stiffness, indicative of decreased active stiffness, suggests activation was likely reduced, causing fascicles to shorten less during MVC.

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.

Changes in Achilles tendon stiffness and energy cost following a prolonged run in trained distance runners

During prolonged running, the magnitude of Achilles tendon (AT) length change may increase, resulting in increased tendon strain energy return with each step. AT elongation might also affect the magnitude of triceps surae (TS) muscle shortening and shortening velocity, requiring greater activation and increased muscle energy cost. Therefore, we aimed to quantify the tendon strain energy return and muscle energy cost necessary to allow energy storage to occur prior to and following prolonged running. 14 trained male (n = 10) and female (n = 4) distance runners (24±4 years, 1.72±0.09 m, 61±10 kg, [Formula: see text] 64.6±5.8 ml•kg-1•min-1) ran 90 minutes (RUN) at approximately 85% of lactate threshold speed (sLT). Prior to and following RUN, AT stiffness and running energy cost (Erun) at 85% sLT were determined. AT energy return was calculated from AT stiffness, measured with dynamometry and ultrasound and estimated TS force during stance. TS energy cost was estimated on the basis of AT force and assumed crossbridge mechanics and energetics. Following RUN, AT stiffness was reduced from 328±172 N•mm-1 to 299±148 N•mm-1 (p = 0.022). Erun increased from 4.56±0.32 J•kg-1•m-1 to 4.62±0.32 J•kg-1•m-1 (p = 0.049). Estimated AT energy return was not different following RUN (p = 0.99). Estimated TS muscle energy cost increased significantly by 11.8±12.3 J•stride-1, (p = 0.0034), accounting for much of the post-RUN increase in Erun (8.6±14.5 J•stride-1,r2 = 0.31). These results demonstrate that a prolonged, submaximal run can reduce AT stiffness and increase Erun in trained runners, and that the elevated TS energy cost contributes substantially to the elevated Erun.

Patellar tendon properties distinguish elite from non-elite soccer players and are related to peak horizontal but not vertical power

PURPOSE

To investigate potential differences in patellar tendon properties between elite and non-elite soccer players, and to establish whether tendon properties were related to power assessed during unilateral jumps performed in different directions.

METHODS

Elite (n = 16; age 18.1 ± 1.0 years) and non-elite (n = 13; age 22.3 ± 2.7 years) soccer players performed vertical, horizontal-forward and medial unilateral countermovement jumps (CMJs) on a force plate. Patellar tendon (PT) cross-sectional area, elongation, strain, stiffness, and Young's modulus (measured at the highest common force interval) were assessed with ultrasonography and isokinetic dynamometry.

RESULTS

Elite demonstrated greater PT elongation (6.83 ± 1.87 vs. 4.92 ± 1.88 mm, P = 0.011) and strain (11.73 ± 3.25 vs. 8.38 ± 3.06%, P = 0.009) than non-elite soccer players. Projectile range and peak horizontal power during horizontal-forward CMJ correlated positively with tendon elongation (r = 0.657 and 0.693, P < 0.001) but inversely with Young's modulus (r = - 0.376 and - 0.402; P = 0.044 and 0.031). Peak medial power during medial CMJ correlated positively with tendon elongation (r = 0.658, P < 0.001) but inversely with tendon stiffness (r = - 0.368, P = 0.050).

CONCLUSIONS

Not only does a more compliant patellar tendon appear to be an indicator of elite soccer playing status but it may also facilitate unilateral horizontal-forward and medial, but not vertical CMJ performance. These findings should be considered when prescribing talent selection and development protocols related to direction-specific power in elite soccer players.

Correlation of some predisposing intrinsic conditions with the morphological integrity of the Achilles tendon

BACKGROUND

Most studies have focused on ill-tendons with a little insight on how intrinsic factors correlate with the Achilles tendon (AT) morphology.

AIM

This study aims at establishing how blood pressure (BP), blood glucose (BG), and body mass index (BMI) correlate with the morphology of the AT with emphasis on width changes.

MATERIALS AND METHODS

Participants were volunteers who were recruited during and after an organized health fair by the Medical Students' body of All Saints University, School of Medicine, Commonwealth of Dominica. A total of 336 people, consisting of 135 males and 201 females volunteered for the study. The most dominant age group was between 60 and 65 years. A self-administered questionnaire was used to acquire necessary information, and a preliminary clinical procedure was used to check for BP, BG, and BMI. Ultrasound examination was done in B-mode using a linear array high-frequency probe with a mediolateral approach at the AT.

RESULTS

Among the participants, 42.68%, 69.75%, and 30.38% had normal BP, BG, and BMI readings, respectively. BP, BG, and BMI statistically supported the hypothesis. Individuals with extreme BP, BG, and BMI had their AT width wider when compared with individuals with normal systemic readings. Sonographic examination revealed most participants with normal tendon morphology while some identifiable changes were observed among others.

CONCLUSION

This study suggests that BP, BG, and BMI could affect the morphological integrity of the AT. It indicates that asymptomatic high blood sugar and BP could weaken the AT, leading to pain which may appear unrelated to the physician and patient.

The influence of long distance running on sonographic joint and tendon pathology: results from a prospective study with marathon runners

Background

The impact of physical exercise on joints and tendons is still a matter of debate. The aim of this study was to investigate with ultrasound the acute effects of extreme physical exercise on knee and ankle joints and their surrounding structures in trained athletes.

Methods

Participants of the Munich marathon were examined by arthrosonography before and after long distance running. Ultrasound assessment included grey scale and power Doppler examination of the knee and talocrural joints with surrounding tendons. Findings consistent with joint effusion, tendon and/or entheseal pathologies were documented. In addition to the ultrasound evaluation, information on training habits and past or present arthralgia or joint swelling was gathered.

Results

One Hundred Five runners completed both the pre- and post-excercise ultrasound assessments (baseline and follow-up), resulting in the sonographic evaluation of 420 knee and talocrural joints. At baseline, 105 knee (50) and 38 talocrural joints (18.1) showed effusions, compared to 100 knee (47.6) and 33 talocrural joints (15.7 %) at follow-up. The differences were not significant (p > 0.05 each). Effusion size did not correlate with the timepoint of ultrasound assessment and was independent of covariates such as gender, age or running distance. Hypervascularity of the patellar tendon was detected in 21 cases (10.0 %) at follow-up in contrast to one at baseline (p < 0.001). This observation was more frequent in male than in female participants (p < 0.05).

Conclusions

Acute physical stress is significantly associated with hypervascularity of the patellar tendon. No significant changes of synovial effusion were detected in knee and talocrural joints.

Immediate effects of whole body vibration on patellar tendon properties and knee extension torque

PURPOSE

Reports about the immediate effects of whole body vibration (WBV) exposure upon torque production capacity are inconsistent. However, the changes in the torque-angle relationship observed by some authors after WBV may hinder the measurement of torque changes at a given angle. Acute changes in tendon mechanical properties do occur after certain types of exercise but this hypothesis has never been tested after a bout of WBV. The purpose of the present study was to investigate whether tendon compliance is altered immediately after WBV, effectively shifting the optimal angle of peak torque towards longer muscle length.

METHODS

Twenty-eight subjects were randomly assigned to either a WBV (n = 14) or a squatting control group (n = 14). Patellar tendon CSA, stiffness and Young's modulus and knee extension torque-angle relationship were measured using ultrasonography and dynamometry 1 day before and directly after the intervention. Tendon CSA was additionally measured 24 h after the intervention to check for possible delayed onset of swelling.

RESULTS

The vibration intervention had no effects on patellar tendon CSA, stiffness and Young's modulus or the torque-angle relationship. Peak torque was produced at ~70° knee angle in both groups at pre- and post-test. Additionally, the knee extension torque globally remained unaffected with the exception of a small (-6%) reduction in isometric torque at a joint angle of 60°.

CONCLUSION

The present results indicate that a single bout of vibration exposure does not substantially alter patellar tendon properties or the torque-angle relationship of knee extensors.

Early changes in Achilles tendon behaviour in vivo following downhill backwards walking

Downhill backwards walking causes repeated, cyclical loading of the muscle-tendon unit. The effect this type of repeated loading has on the mechanical behaviour of the Achilles tendon is presently unknown. This study aimed to investigate the biomechanical response of the Achilles tendon aponeurosis complex following a downhill backwards walking protocol. Twenty active males (age: 22.3 ± 3.0 years; mass: 74.7 ± 5.6 kg; height: 1.8 ± 0.7 m) performed 60 min of downhill (8.5°), backwards walking on a treadmill at -0.67 m · s(-1). Data were collected before, immediately post, and 24-, 48- and 168-h post-downhill backwards walking. Achilles tendon aponeurosis elongation, strain and stiffness were measured using ultrasonography. Muscle force decreased immediately post-downhill backward walking (P = 0.019). There were increases in Achilles tendon aponeurosis stiffness at 24-h post-downhill backward walking (307 ± 179.6 N · mm(-1), P = 0.004), and decreases in Achilles tendon aponeurosis strain during maximum voluntary contraction at 24 (3.8 ± 1.7%, P = 0.008) and 48 h (3.9 ± 1.8%, P = 0.002) post. Repeated cyclical loading of downhill backwards walking affects the behaviour of the muscle-tendon unit, most likely by altering muscle compliance, and these changes result in tendon stiffness increases.

Prevalence of morphological and mechanical stiffness alterations of mid Achilles tendons in asymptomatic marathon runners before and after a competition

OBJECTIVE

To determine the prevalence of morphological and mechanical stiffness alterations at the mid Achilles tendon in asymptomatic marathon runners before and after a competition. To assess the relationship between pre-existing Achilles tendon alterations and pain after running.

MATERIALS AND METHODS

All marathon runners from a local running club who were participating in the Melbourne Marathon 2013 (full marathon category) were invited for conventional ultrasound and sonoelastography 1 week leading up to the marathon and again within 3 days post-marathon. Another group of active, healthy individuals not involved in running activities were recruited as controls. Intratendinous morphological (tendon thickness, hypoechogenicities), Doppler as well as stiffness properties of the Achilles were recorded. Achilles tendon pain was evaluated using the visual analogue scale (VAS) and Victorian Institute of Sports Assessment-Achilles (VISA-A).

RESULTS

Twenty-one asymptomatic runners (42 Achilles tendons) and 20 healthy controls (40 Achilles tendons) were examined. On the pre-marathon evaluation, runners showed significantly more morphological changes on B-mode ultrasound compared to the controls (p < 0.001). Marathon running induced a significant reduction in tendon stiffness (p = 0.049) and an increase in Doppler signals (p = 0.036). Four runners (4/21, 19%) reported Achilles tendon pain after the race [VAS 4.0 (±1.9), VISA 74.2 (±10.1)]. Reduced tendon stiffness at baseline was associated with post-marathon Achilles tendon pain (p = 0.016).

CONCLUSION

Marathon runners demonstrate a higher prevalence of morphological alterations compared to non-runners. Marathon running caused a significant change in Achilles tendon stiffness and Doppler signals. Pre-existing soft Achilles tendon properties on sonoelastography may be a predisposing risk for development of symptoms post-running.

Experimental study of the characteristics of a novel mesh suture

Background

The failure of sutures to maintain tissue in apposition is well characterized in hernia repairs. A mesh suture designed to facilitate tissue integration into and around the filaments may improve tissue hold and decrease suture pull‐through.

Methods

In vitro, the sutures were compared for resistance to pull‐through in ballistics gel. In vivo, closure of midline laparotomy incisions was done with both sutures in 11 female pigs. Tissue segments were subsequently subjected to mechanical and histological testing.

Results

The mesh suture had tensile characteristics nearly identical to those of 0‐polypropylene suture. Mesh suture demonstrated greater resistance to pull‐through than standard suture (mean(s.d.) 4·27(0·42) versus 2·23(0·48) N; P < 0·001) in vitro. In pigs, the ultimate tensile strength for repaired linea alba at 8 days was higher with mesh suture (320(57) versus 160(56) N; P < 0·001), as was the work to failure (24·6(14·2) versus 7·3(3·7) J; P < 0·001) and elasticity (128(9) versus 72(7) N/cm; P < 0·001) in comparison with 0‐polypropylene suture. Histological examination at 8 and 90 days showed complete tissue integration of the mesh suture.

Conclusion

The novel mesh suture structure increased the strength of early wound healing in an experimental model.

Effects of running on human Achilles tendon length-tension properties in the free and gastrocnemius components

The elastic properties of the human Achilles tendon are important for locomotion; however, in vitro tests suggest that repeated cyclic contractions lead to tendon fatigue - an increase in length in response to stress applied. In vivo experiments have not, however, demonstrated mechanical fatigue in the Achilles tendon, possibly due to the limitations of using two-dimensional ultrasound imaging to assess tendon strain. This study used freehand three-dimensional ultrasound (3DUS) to determine whether the free Achilles tendon (calcaneus to soleus) or the gastrocnemius tendon (calcaneus to gastrocnemius) demonstrated tendon fatigue after running exercise. Participants (N=9) underwent 3DUS scans of the Achilles tendon during isometric contractions at four ankle torque levels (passive, and 14, 42 and 70 N m) before and after a 5 km run at a self-selected pace (10-14 km h(-1)). Running had a significant main effect on the length of the free Achilles tendon (P<0.01) with a small increase in length across the torque range. However, the mean lengthening effect was small (<1%) and was not accompanied by a change in free tendon stiffness. There was no significant change in the length of the gastrocnemius tendon or the free tendon cross-sectional area. While the free tendon was shown to lengthen, the lack of change in stiffness suggests the tendon exhibited mechanical creep rather than fatigue. These effects were much smaller than those predicted from in vitro experiments, possibly due to the different loading profile encountered and the ability of the tendon to repair in vivo.

The role of hind limb tendons in gibbon locomotion: springs or strings?

Tendon properties have an important effect on the mechanical behaviour of muscles, with compliant tendons allowing near-isometric muscle contraction and facilitating elastic energy storage and recoil. Stiff tendons, in contrast, facilitate rapid force transfer and precise positional control. In humans, the long Achilles tendon contributes to the mechanical efficiency of running via elastic energy storage and recovery, and its presence has been linked to the evolution of habitual bipedalism. Gibbons also possess relatively long hind limb tendons; however, their role is as yet unknown. Based on their large dimensions, and inferring from the situation in humans, we hypothesize that the tendons in the gibbon hind limb will facilitate elastic energy storage and recoil during hind-limb-powered locomotion. To investigate this, we determined the material properties of the gibbon Achilles and patellar tendon in vitro and linked this with available kinematic and kinetic data to evaluate their role in leaping and bipedalism. Tensile tests were conducted on tendon samples using a material testing machine and the load-displacement data were used to calculate stiffness, Young's modulus and hysteresis. In addition, the average stress-in-life and energy absorption capacity of both tendons were estimated. We found a functional difference between the gibbon Achilles and patellar tendon, with the Achilles tendon being more suitable for elastic energy storage and release. The patellar tendon, in contrast, has a relatively high hysteresis, making it less suitable to act as elastic spring. This suggests that the gibbon Achilles tendon might fulfil a similar function as in humans, contributing to reducing the locomotor cost of bipedalism by acting as elastic spring, while the high stiffness of the patellar tendon might favour fast force transfer upon recoil and, possibly, enhance leaping performance.

Viscoelastic properties of the Achilles tendon in vivo

It has been postulated that human tendons are viscoelastic and their mechanical properties time-dependent. Although Achilles tendon (AT) mechanics are widely reported, there is no consensus about AT viscoelastic properties such as loading rate dependency or hysteresis, in vivo. AT force-elongation characteristics were determined from 14 subjects in an ankle dynamometer at different loading rates using motion capture assisted ultrasonography. AT stiffness and elongation were determined between 10 - 80% of maximum voluntary contraction (MVC) force at fast and slow loading rates. As subjects were unable to consistently match the target unloading rate in the slow condition, AT hysteresis was only calculated for the fast rate. There was a significant difference between the fast and the slow loading rates: 120 ± 6 vs. 21 ± 1% of MVC s(-1) (mean ± standard error), respectively. However, neither stiffness (193 ± 18 N mm(-1) vs. 207 ± 22 N mm(-1)) nor elongation at any force level (13.0 ± 1.2 mm vs. 14.3 ± 0.9 mm at 80% of MVC) were significantly different between the fast and slow loading rates. Tendon hysteresis at the fast rate was 5 ± 2%. As stiffness was not sensitive to loading rate and hysteresis was small, it was concluded that elastic properties prevail over viscous properties in the human AT. The current results support the idea that AT stiffness is independent of loading rate.