Achilles Tendon Strain Research Articles

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.

Effect of Training-Induced Changes in Achilles Tendon Stiffness on Muscle-Tendon Behavior During Landing.

During rapid deceleration of the body, tendons buffer part of the elongation of the muscle–tendon unit (MTU), enabling safe energy dissipation via eccentric muscle contraction. Yet, the influence of changes in tendon stiffness within the physiological range upon these lengthening contractions is unknown. This study aimed to examine the effect of training-induced stiffening of the Achilles tendon on triceps surae muscle–tendon behavior during a landing task. Twenty-one male subjects were assigned to either a 10-week resistance-training program consisting of single-leg isometric plantarflexion (n = 11) or to a non-training control group (n = 10). Before and after the training period, plantarflexion force, peak Achilles tendon strain and stiffness were measured during isometric contractions, using a combination of dynamometry, ultrasound and kinematics data. Additionally, testing included a step-landing task, during which joint mechanics and lengths of gastrocnemius and soleus fascicles, Achilles tendon, and MTU were determined using synchronized ultrasound, kinematics and kinetics data collection. After training, plantarflexion strength and Achilles tendon stiffness increased (15 and 18%, respectively), and tendon strain during landing remained similar. Likewise, lengthening and negative work produced by the gastrocnemius MTU did not change detectably. However, in the training group, gastrocnemius fascicle length was offset (8%) to a longer length at touch down and, surprisingly, fascicle lengthening and velocity were reduced by 27 and 21%, respectively. These changes were not observed for soleus fascicles when accounting for variation in task execution between tests. These results indicate that a training-induced increase in tendon stiffness does not noticeably affect the buffering action of the tendon when the MTU is rapidly stretched. Reductions in gastrocnemius fascicle lengthening and lengthening velocity during landing occurred independently from tendon strain. Future studies are required to provide insight into the mechanisms underpinning these observations and their influence on energy dissipation.

Effects of Two Plyometric Protocols at Different Surfaces on Mechanical Properties of Achilles Tendon in Children

Objectives: The purpose of this study was to compare the changes in muscle strength and Achilles tendon strain after two plyometric training programs performed on different surfaces in children. Methods: Thirty six children (21 girls, 15 boys) aged 9.30 ± 0.55 years were assigned into a mini-trampoline plyometric group (TPLG), a ground-plyometric group (GPLG) and a control group (CG). The training groups completed a 4-week plyometric intervention (PL) (three-times a week), consisting of hopping exercises performed either on a mini-trampoline (TPLG) or ground (GPLG). Achilles tendon strain, peak ankle plantar flexion torque (PAT), and rate of torque development (RTD) at 3 different angular positions of the ankle (15°, 0° and -15°) were measured before and after training. Results: The main finding of this study was that Achilles tendon strain decreased significantly after plyometric training performed on a mini-trampoline or ground surface ( 25% and 15%, for the TPLG and GPLG, respectively (P < 0.05)). This was accompanied by an increase in maximum ankle MVC torque and an increase in RTD (at 15°, 0° positions) for both experimental groups. Especially, statistically significant increases in PAT (30%) and RTD (14%) (P < 0.05) were found for the TPLG while for the GPLG group the increase was 19 % and 8% for PAT and RTD, respectively (P < 0.05). Conclusions: Both protocols show similar adaptations regardless of the surface of training. Training on elastic surface should be incorporated into exercise programs aiming either to enhance strength performance safely, or to achieve the target goal which is not only the safe performance but also the muscle-tendon system efficiency.

Mechanical muscle and tendon properties of the plantar flexors are altered even in highly functional children with spastic cerebral palsy

BackgroundRecent ultrasound studies found increased passive muscle stiffness and no difference in tendon stiffness in highly impaired children and young adults with cerebral palsy. However, it is not known if muscle and tendon mechanical properties are already altered in highly functional children with cerebral palsy. Therefore, the purpose of this study was to compare the mechanical and material properties of the plantar flexors in highly functional children with cerebral palsy and typically developing children. MethodsBesides strength measurements, ultrasonography was used to assess gastrocnemius medialis and Achilles tendon elongation and stiffness, Achilles tendon stress, strain, and Young's modulus in twelve children with cerebral palsy (GMFCS levels I and II) and twelve typically developing peers during passive dorsiflexion rotations as well as maximum voluntary contractions. FindingsDespite no difference in ankle joint stiffness (P>0.05) between groups, passive but not active Achilles tendon stiffness was significantly decreased (−39%) and a tendency of increased passive muscle stiffness was observed even in highly functional children with cerebral palsy. However, material properties of the tendon were not altered. Maximum voluntary contraction showed reduced plantar flexor strength (−48%) in the cerebral palsy group. InterpretationEven in children with mild spastic cerebral palsy, muscle and tendon mechanical properties are altered. However, it appears that the Achilles tendon stiffness is different only when low forces act on the tendon during passive movements. Although maximum voluntary force is already decreased, forces acting on the Achilles tendon during activity appear to be sufficient to maintain typical material properties.

Evaluation of Achilles Tendon Injuries with Findings from Diagnostic Musculoskeletal Ultrasound in Canines – 43 Cases

&lt;p&gt;&lt;strong&gt;Objective: &lt;/strong&gt;The objective was to describe clinical and ultrasonographic characteristics of canine Achilles tendon injuries.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Background:&lt;/strong&gt; Even though there have been publications describing characteristics of the normal and injured Achilles tendon by diagnostic ultrasound, there has been no previous in-depth ultrasonic evaluation and characterisation of Achilles tendon strains.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Evidentiary value:&lt;/strong&gt; This is a retrospective case series report of 43 dogs that underwent musculoskeletal diagnostic ultrasound evaluation of their strained Achilles tendons, with and without surgical repair.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Methods: &lt;/strong&gt;Data was collected from medical records of patients from August 2009 to May 2016. Inclusion criteria for dogs included a diagnosis of Achilles tendon injury based on the presence of fibre pattern modification within one or more components of the Achilles mechanism on initial diagnostic ultrasound.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Results:&lt;/strong&gt; It was found on the diagnostic ultrasound that Achilles tendon injuries were strictly unilateral in 51.2% (n=22/43) of cases and bilateral on presentation in 48.8% (n=21/43) of cases. 18.2% of the unilateral case progressively became bilateral over time (n=4/22). The injury was partial in 90.7% (n=39/43) of the cases and all three components of the Achilles mechanism were completely disrupted in only 9.3% of the cases (n=4/43). The partial injuries incorporated changes within the fibre patterns of all 3 components of the Achilles in 53.8% (n=21/39) of the cases and alteration of both the gastrocnemius tendon (GT) and common tendon (CT) in 41.0% (n=16/39) of the cases. Grade III strains were predominant (44.3%), followed by grade I (28.6%) and grade II (27.1%). Damage occurred most commonly at the tendino-osseous insertion (77%), with injury occurring less frequently diffusely along the body of the tendon (12.5%) or at the musculotendinous junction (10.5%).&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Conclusion: &lt;/strong&gt;Diagnostic musculoskeletal ultrasound was used to identify lesions of Achilles tendon consistent with different grade of strain, as well as identifying the specific region of injury. Diagnostic ultrasound findings were correlated to the surgical findings and previous literature.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Application:&lt;/strong&gt; Diagnostic musculoskeletal ultrasound provides a non-invasive diagnostic modality for patients suspected of having Achilles tendon strain. Further investigation is needed to establish treatment protocols based on ultrasonographic 3-tier grading scheme for Achilles tendon strain injury.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Abbreviations: &lt;/strong&gt;Common tendon (CT), computed tomography scan (CT scan), gastrocnemius tendon (GT), magnetic resonance imaging (MRI), myotendinous junction (MTJ), superficial digital flexor tendon (SDFT).&lt;/p&gt;&lt;br /&gt; &lt;img src="https://www.veterinaryevidence.org/rcvskmod/icons/oa-icon.jpg" alt="Open Access" /&gt; &lt;img src="https://www.veterinaryevidence.org/rcvskmod/icons/pr-icon.jpg" alt="Peer Reviewed" /&gt;

Novel Physical Therapy Protocol Results in Increased Compressive Strain and Improved Outcomes in Insertional Achilles Tendinopathy

Category: Ankle, Hindfoot, Sports Introduction/Purpose: Insertional Achilles Tendinopathy (IAT) affects 5% of the general population and up to 20% of the athletic population. Despite trials of non-surgical management, over 50% of patients ultimately pursue surgery. Previously in healthy controls it was demonstrated that ankle dorsiflexion tasks increase transverse compressive strain (force perpendicular to the tendon fibers) most in the deep region of the tendon insertion, where IAT is often most severe. Thus the purpose of this study was to utilize a novel physical therapy protocol that combines isometric and eccentric exercises in order to increase transverse compressive strain and decrease axial tensile strain (force parallel to tendon fibers) in patients with IAT and to determine whether this corresponds with improved patient outcome scores. Methods: Forty-two patients with IAT were enrolled in the study from May 2014 to June 2016, of which twenty-seven patients (mean age: 56.7 + 9.9 years, BMI: 29.6 + 5.9, 56% women) completed the study. A subset (n=15, mean age 58.9 + 8.6 years, BMI: 30.0 + 4.0, 47% women) underwent ultrasound elastography to determine transverse compressive and axial tensile strain in the Achilles tendon during dorsiflexion tasks. Patients were then placed on a physical therapy protocol that focused on progressive loading of the Achilles tendon while avoiding ankle dorsiflexion. Seated isometric plantar flexion, bilateral eccentric heel lowering, and single limb heel lowering exercises were utilized. Questionnaires validated for use in Achilles tendinopathy, the Victorian Institute of Sport Assessment – Achilles (VISA-A) and the Foot and Ankle Ability Measure (FAAM), were completed at the beginning and at the completion of the study. Results: Twenty-three of 27 subjects that completed the study, had clinically significant improvements in their VISA-A (mean change 19.3) or FAAM ADL and sports scores (mean change 16.2 and 22.6, respectively). Ultrasound elastography revealed that the deep region of the Achilles tendon experienced more transverse compressive strain and less axial tensile strain compared to the superficial portion of the tendon when standing. Completion of the physical therapy program resulted in increased transverse compressive strain in the superficial Achilles tendon compared to the pre-therapy value when standing (mean change 52%, p=0.043). Moreover, there was a decrease in axial tensile strain within the deep portion of the tendon in response to physical therapy (mean change 53% p=0.0434). Conclusion: Treatment of IAT patients with a physical therapy protocol utilizing a combination of isometric and eccentric exercises results in improved outcomes, as measured by VISA-A and FAAM questionnaires. Furthermore, ultrasound elastography suggests that while the physical therapy protocol increases the transverse compressive strain in the superficial portion of the Achilles tendon, it results in decreased axial tensile strain in the deep portion of the tendon. Therefore, it is likely that the combination of these two exercise modalities result in the improved clinical outcomes observed in our patients with IAT after undergoing this physical therapy protocol.

Conditioning hops increase triceps surae muscle force and Achilles tendon strain energy in the stretch-shortening cycle.

Postactivation potentiation can improve athletic performance, but the underlying mechanisms are poorly understood. This study investigated the effect of conditioning hops on triceps surae muscle force and tendon strain and its contribution to potentiated stretch-shortening cycle (SSC) performance. Thirty-two subjects participated in two experiments. In both experiments, subjects performed three drop jumps (DJs) after prior conditioning with 10 maximal hops, three unconditioned DJs served as control. Ground reaction forces, kinematics, and triceps surae electromyographic activity were recorded. Ultrasound imaging was used to determine fascicle lengths (FASC) of the gastrocnemius (GM) and soleus muscles (experiment 1) and the length of the Achilles tendon (experiment 2) during the DJs. DJ height after the conditioning hops was significantly higher compared to control DJs (experiment 1: +12% and experiment 2: +19%). A significantly shorter GM FASC during the DJs performed after the conditioning hops coincided with an increased force acting on the triceps surae muscle. Moreover, the triceps surae muscle-tendon unit (MTU) showed increased energy absorption during the eccentric phase of the DJs and increased energy release during the concentric phase. The second experiment revealed a higher Achilles tendon strain in DJs performed after the conditioning hops compared to control DJs. No significant differences in muscle activities were observed. The shorter FASC in GM and the larger Achilles tendon strain facilitated MTU energy transfer from the eccentric to the concentric phase during the DJ. Thereby, conditioning hops improved SSC efficacy and DJ performance.

Strain mapping in the Achilles tendon – A systematic review

Achilles tendinopathy remains one of the most prevalent overuse injuries in elite as well as recreational athletes. Regardless of the fact that the aetiology of tendinopathy has not been fully understood, therapeutic mechanical loading programs have emerged as being the treatment of choice. In this light, mechanical properties of the tendon and their response to changes in loading or unloading have been the subject of many previous investigations. One of these properties often investigated is strain, a measure of relative deformation. By means of a systematic review, an overview was given of research in this field, with a primary objective to list the methods used and secondary aim to synthesize data on strain mapping in the Achilles tendon. Following the guidelines of the PRISMA statement, 47 articles were found appropriate for qualitative assessment. Achilles tendon strain has been investigated across a variety of contexts, including the response to exercise, walking, unloading, ageing, hormonal changes and weight. Only three studies investigated the effect of the presence of tendinopathy on strain. Ultrasound was the most often used imaging modality to measure or estimate strain. Further methodological parameters, e.g. the location of measurement, differed greatly between all different studies. Nearly all studies considered global strain. Some studies investigated the transverse strain response of the Achilles tendon. Recently, however, the role of local – intratendinous – strain distribution has been found to be of critical importance and further studies should focus on imaging modalities to investigate these local changes.

High variability in strain estimation errors when using a commercial ultrasound speckle tracking algorithm on tendon tissue.

Ultrasound speckle tracking offers a non-invasive way of studying strain in the free Achilles tendon where no anatomical landmarks are available for tracking. This provides new possibilities for studying injury mechanisms during sport activity and the effects of shoes, orthotic devices, and rehabilitation protocols on tendon biomechanics. To investigate the feasibility of using a commercial ultrasound speckle tracking algorithm for assessing strain in tendon tissue. A polyvinyl alcohol (PVA) phantom, three porcine tendons, and a human Achilles tendon were mounted in a materials testing machine and loaded to 4% peak strain. Ultrasound long-axis cine-loops of the samples were recorded. Speckle tracking analysis of axial strain was performed using a commercial speckle tracking software. Estimated strain was then compared to reference strain known from the materials testing machine. Two frame rates and two region of interest (ROI) sizes were evaluated. Best agreement between estimated strain and reference strain was found in the PVA phantom (absolute error in peak strain: 0.21 ± 0.08%). The absolute error in peak strain varied between 0.72 ± 0.65% and 10.64 ± 3.40% in the different tendon samples. Strain determined with a frame rate of 39.4 Hz had lower errors than 78.6 Hz as was the case with a 22 mm compared to an 11 mm ROI. Errors in peak strain estimation showed high variability between tendon samples and were large in relation to strain levels previously described in the Achilles tendon.

Ultrasound strain mapping of Achilles tendon compressive strain patterns during dorsiflexion

Heel lifts are commonly prescribed to patients with Achilles tendinopathy, yet little is known about the effect on tendon compressive strain. The purposes of the current study were to (1) develop a valid and reliable ultrasound elastography technique and algorithm to measure compressive strain of human Achilles tendon in vivo, (2) examine the effects of ankle dorsiflexion (lowering via controlled removal of a heel lift and partial squat) on compressive strain of the Achilles tendon insertion and (3) examine the relative compressive strain between the deep and superficial regions of the Achilles tendon insertion. All tasks started in a position equivalent to standing with a 30mm heel lift. An ultrasound transducer positioned over the Achilles tendon insertion was used to capture radiofrequency images. A non-rigid image registration-based algorithm was used to estimate compressive strain of the tendon, which was divided into 2 regions (superficial, deep). The bland-Altman test and intraclass correlation coefficient were used to test validity and reliability. One-way repeated measures ANOVA was used to compare compressive strain between regions and across tasks. Compressive strain was accurately and reliably (ICC>0.75) quantified. There was greater compressive strain during the combined task of lowering and partial squat compared to the lowering (P=.001) and partial squat (P<.001) tasks separately. There was greater compressive strain in the deep region of the tendon compared to the superficial for all tasks (P=.001). While these findings need to be examined in a pathological population, heel lifts may reduce tendon compressive strain during daily activities.

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

ABSTRACTDownhill 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.

Estimation of local strain of Achilles tendon during exercise with individual structure geometry and tendon force date by finite element analysis

Estimation of local strain of Achilles tendon during exercise with individual structure geometry and tendon force date by finite element analysis

Using digital image correlation to examine in-vivo localised Achilles tendon strain

Using digital image correlation to examine in-vivo localised Achilles tendon strain

Achilles tendon strain energy in distance running: consider the muscle energy cost.

The return of tendon strain energy is thought to contribute to reducing the energy cost of running (Erun). However, this may not be consistent with the notion that increased Achilles tendon (AT) stiffness is associated with a lower Erun. Therefore, the purpose of this study was to quantify the potential for AT strain energy return relative to Erun for male and female runners of different abilities. A total of 46 long distance runners [18 elite male (EM), 12 trained male (TM), and 16 trained female (TF)] participated in this study. Erun was determined by indirect calorimetry at 75, 85, and 95% of the speed at lactate threshold (sLT), and energy cost per stride at each speed was estimated from previously reported stride length (SL)-speed relationships. AT force during running was estimated from reported vertical ground reaction force (Fz)-speed relationships, assuming an AT:ground reaction force moment arm ratio of 1.5. AT elongation was quantified during a maximal voluntary isometric contraction using ultrasound. Muscle energy cost was conservatively estimated on the basis of AT force and estimated cross-bridge mechanics and energetics. Significant group differences existed in sLT (EM > TM > TF; P < 0.001). A significant group × speed interaction was found in the energy storage/release per stride (TM > TF > EM; P < 0.001), the latter ranging from 10 to 70 J/stride. At all speeds and in all groups, estimated muscle energy cost exceeded energy return (P < 0.001). These results show that during distance running the muscle energy cost is substantially higher than the strain energy release from the AT.

Effect of Muscle Energy Technique to Improve Flexibility of Gastro-Soleus Complex in Plantar Fasciitis: A Randomised Clinical, Prospective Study Design

Background: Plantar fasciitis is considered to be an overuse syndrome as it develops over time and is a result of repeated stress that exceeds the body's inherent capacity to repair and adapt which eventually leads to the failure of the ligaments, bones and muscles. Functional risk factors include tightness in gastronemius, soleus and weakness of intrinsic foot muscles because limited dorsiflexion due to tight Achilles tendon strains the plantar fascia. short-term treatments such as muscle stretches are regularly used to alleviate symptoms during this interim period. An increase in ankle range of motion may reduce the symptoms of plantar heel pain by reducing the strain in the plantar fascia.

Achilles-Tendon Strain Most Common Injury in Sports; Cause, Symptems and Management

Background: Achilles tendon strain actually identifies itself. First a strain is milder always than a sprain and a strain affects tendons while sprains affect ligaments. A strain involves hyperextension of a tendon or mild tearing of its fibers. Methods: Analytical methods was used for this article by reviewing relevant publications, primarily based on the online sports medicine journals available on Internet, Wikipedia, Elsevier, PubMed, Google Scholar and National Sports Injury Center Saffdarjang Hospital. Conclusion: This review will provide an overview of the Achilles tendon Sprain and their immediate management on playfield. By this sports personals i.e. coach, trainer and player itself would be able to identify this injury. And will give a better understanding about the sign and symptoms of this injury. Approaches should be used to help in sports training and to avoid injury. Good understanding of the injury and their management may be used in the sports to establish safe and effective training guidelines for sportsman.

Biomechanical Simulation of Achilles Tendon Strains during Hurdling

Hurdling is one of the top athletic games with high injury risks, especially the Achilles tendon injury. The purpose of the study was to quantify the Achilles tendon strains using a biomechanical simulation approach, which incorporate motion capture technique and musculoskeletal modeling. The finding indicates that the main muscles of Achilles tendon, gastronomic and soleus, change greatly in muscle length during the hurdling takeoff. The peak angle of the knee and angle was observed at the end of foot touching phase. The results obtained in this study can serve as a basis for further research on Achilles tendon rupture.

Identifying factors related to Achilles tendon stress, strain, and stiffness before and after 6 months of growth in youth 10–14 years of age

The purposes of this study were (1) determine if youth peak Achilles tendon (AT) strain, peak AT stress, and AT stiffness, measured during an isometric plantar flexion, differed after six months (mos) of growth, and (2) determine if sex, physical activity level (Physical Activity Questionnaire (PAQ-C)), and/or growth rate (GR) were related to these properties. AT stress, strain, and stiffness were quantified in 20 boys (13.47±0.81 years) and 22 girls (11.18±0.82 years) at 2 times (0 and 6 mos). GR (change in height in 6 mos) was not significantly different between boys and girls (3.5±1.4 and 3.4±1.1cm/6 mos respectively). Peak AT strain and stiffness (mean 3.8±0.4% and 128.9±153.6N/mm, respectively) did not differ between testing sessions or sex. Peak AT stress (22.1±2.4 and 24.0±2.1MPa at 0 and 6 mos, respectively) did not differ between sex and increased significantly at 6 mos due to a significant decrease in AT cross-sectional area (40.6±1.3 and 38.1±1.6mm2 at 0 and 6 mos, respectively) with no significant difference in peak AT force (882.3±93.9 and 900.3± 65.5N at 0 and 6 mos, respectively). Peak AT stress was significantly greater in subjects with greater PAQ-C scores (9.1% increase with 1 unit increase in PAQ-C score) and smaller in subjects with faster GRs (13.8% decrease with 1cm/6 mos increase in GR). These results indicate that of the AT mechanical properties quantified, none differed between sex, and only peak AT stress significantly differed after 6 months and was related to GR and physical activity.

The Effects of Orthotic Heel Lifts on Achilles Tendon Force and Strain During Running

This study assessed the effects of orthotic heel lifts on Achilles tendon (AT) force and strain during running. Ten females ran barefoot over a force plate in three conditions: no heel lifts (NHL), with 12 mm heel lifts (12HL) and with 18 mm heel lifts (18HL). Kinematics for the right lower limb were collected (200 Hz). AT force was calculated from inverse dynamics. AT strain was determined from kinematics and ultrasound images of medial gastrocnemius (50 Hz). Peak AT strain was less for 18HL (5.5 ± 4.4%) than for NHL (7.4 ± 4.2%) (p = .029, effect size [ES] = 0.44) but not for 12HL (5.8 ± 4.8%) versus NHL (ES = 0.35). Peak AT force was significantly (p = .024, ES = 0.42) less for 18HL (2382 ± 717 N) than for NHL (2710 ± 830 N) but not for 12HL (2538 ± 823 N, ES = 0.21). The 18HL reduced ankle dorsiflexion but not flexion-extension ankle moments and increased the AT moment arm compared with NHL. Thus, 18HL reduced force and strain on the AT during running via a reduction in dorsiflexion, which lengthened the AT moment arm. Therefore, heel lifts could be used to reduce AT loading and strain during the rehabilitation of AT injuries.

Dynamic creep and pre-conditioning of the Achilles tendon in-vivo

Warm-up exercises are often advocated prior to strenuous exercise, but the warm-up duration and effect on muscle–tendon behavior are not well defined. The gastrocnemius–Achilles tendon complexes of 18 subjects were studied to quantify the dynamic creep response of the Achilles tendon in-vivo and the warm-up dose required for the Achilles tendon to achieve steady-state behavior. A custom testing chamber was used to determine each subject's maximum voluntary contraction (MVC) during an isometric ankle plantar flexion effort. The subject's right knee and ankle were immobilized for one hour. Subjects then performed over seven minutes of cyclic isometric ankle plantar flexion efforts equal to 25–35% of their MVC at a frequency of 0.75 Hz. Ankle plantar flexion effort and images from dual ultrasound probes located over the gastrocnemius muscle–Achilles tendon and the calcaneus–Achilles tendon junction were acquired for eight seconds at the start of each sequential minute of the activity. Ultrasound images were analyzed to quantify the average relative Achilles tendon strain at 25% MVC force ( ε 25%MVC) for each minute. The ε 25%MVC increased from 0.3% at the start of activity to 3.3% after seven minutes, giving a total dynamic creep of ~3.0%. The ε 25%MVC increased by more than 0.56% per minute for the first five minutes and increased by less than 0.13% per minute thereafter. Therefore, following a period of inactivity, a low intensity warm-up lasting at least six minutes or producing 270 loading cycles is required for an Achilles tendon to reach a relatively steady-state behavior.