Achilles Tendon Strain Research Articles

Modelling activity dependent diametral strain in Achilles tendon

The Achilles tendon is a viscoelastic tissue that typically experiences 3500±1700 cyclic loads per day from intermittent periods of ambulatory activity. Typically, peak tensile loads exceed three times body weight and average about 1500N during stance, which lasts for approximately 0.6s, followed by a 0.2s unloaded swing phase. Viscoelastic materials respond to external load (stress) in a time-dependent manner commonly referred to as creep deformation (strain) and recover slowly when unloaded. This can be observed in vivo by monitoring changes in tendon diameter using quantitative ultrasonography and is referred to here as diametral strain.

The effects of orthotic heel lifts on Achilles tendon force and strain during running

The effects of orthotic heel lifts on Achilles tendon force and strain during running

Effects of estrogen on the mechanical behavior of the human Achilles tendon in vivo

The purpose of this study was to elucidate the effect of normal fluctuating [non-monophasic oral contraceptive pill (MOCP) users] and low, consistent (MOCP users) endogenous plasma estrogen levels on the strain behavior of the Achilles tendon in vivo. Twenty women (age 28.0 +/- 4.2 yr, height 1.67 +/- 0.07 m, mass 61.6 +/- 6.8 kg) who had been using the MOCP for at least 12 mo together with 20 matched women who were non-MOCP users (age 31.9 +/- 7.3 yr, height 1.63 +/- 0.05 m, mass 62.5 +/- 5.9 kg) participated in this study. Non-MOCP users were tested at the time of lowest (menstruation) and highest (approximately same as ovulation) estrogen, whereas MOCP users, who exhibited constant and attenuated endogenous estrogen levels, were tested at day 1 and day 14 of their cycle. At each test session, maximal isometric plantarflexion efforts were performed on a calf-raise apparatus while synchronous real-time ultrasonography of the triceps surae aponeurosis was recorded. Achilles tendon strain (%) was calculated by dividing tendon displacement during plantarflexion by resting tendon length. Repeated-measures ANOVA revealed a significant (P < 0.05) main effect of subject group with significantly lower Achilles strain (25.5%) in the MOCP users compared with the non-MOCP users. In conclusion, acute fluctuations in plasma estrogen across the menstrual cycle in non-MOCP users did not alter the strain behavior of the Achilles tendon. Conversely, long-term exposure to attenuated estrogen in MOCP users resulted in a decrease in Achilles tendon strain, which is thought to be attributed to the effects of endogenous estrogen on collagen synthesis. These findings have a number of important functional and clinical implications.

217 Reliability of an In Vivo measure of Achilles Tendon strain

217 Reliability of an In Vivo measure of Achilles Tendon strain

Achilles Tendon Adaptation during Strength Training in Young Adults

Tendons are specialized musculoskeletal structures responsible for transferring forces between muscles and bones. To maintain joint mechanics and structural integrity, tendons must adapt to changes in mechanical loading, but little is known about the interaction between muscle and tendon adaptations in vivo. We tested the hypothesis that tendons adapt to changes in muscle strength to maintain strains within a preferred operating range. The right lower leg of 10 male subjects, age 24.9 +/- 3.4 yr (mean +/- SD), mass 78.1 +/- 9.7 kg, and height 176.5 +/- 7.2 cm, were tested before and during weeks 1, 2, 4, 6, and 8 of an 8-wk ankle plantar flexion strength training program. Subjects performed isometric plantar flexion efforts slowly ramping up from rest to a maximum effort. Plantar flexion force, Achilles tendon deformation, and cross-sectional area were measured. Triceps surae muscle force (assumed equal to Achilles tendon force), normalized force, and Achilles tendon stress and strain were calculated. Achilles tendon strains during maximum plantar flexion efforts (epsilon(max)) were compared between weeks to test the hypothesis. Repeated-measures ANOVA was used to test for significant changes during the 8 wk, with alpha = 0.05 used as the criterion for significance. There were no significant differences in the group's mean percent or absolute change in epsilon(max) (P = 0.607 and 0.351, respectively) despite a 21.4% average increase in muscle strength during the 8 wk. This is the first study that quantifies Achilles tendon strain throughout a strength training program. Findings indicate that the Achilles tendon adapts quickly to muscle strength training and experiences relatively little change in peak strain despite large increases in muscle strength.

Interactions between the human gastrocnemius muscle and the Achilles tendon during incline, level and decline locomotion

Muscles are required to perform or absorb mechanical work under different conditions. However the ability of a muscle to do this depends on the interaction between its contractile components and its elastic components. In the present study we have used ultrasound to examine the length changes of the gastrocnemius medialis muscle fascicle along with those of the elastic Achilles tendon during locomotion under different incline conditions. Six male participants walked (at 5 km h(-1)) on a treadmill at grades of -10%, 0% and 10% and ran (at 10 km h(-1)) at grades of 0% and 10%, whilst simultaneous ultrasound, electromyography and kinematics were recorded. In both walking and running, force was developed isometrically; however, increases in incline increased the muscle fascicle length at which force was developed. Force was developed at shorter muscle lengths for running when compared to walking. Substantial levels of Achilles tendon strain were recorded in both walking and running conditions, which allowed the muscle fascicles to act at speeds more favourable for power production. In all conditions, positive work was performed by the muscle. The measurements suggest that there is very little change in the function of the muscle fascicles at different slopes or speeds, despite changes in the required external work. This may be a consequence of the role of this biarticular muscle or of the load sharing between the other muscles of the triceps surae.

The role of insurance data in setting priorities for netball injury prevention strategies

The aim of this study was to investigate insurance records for a one-year period to determine the injury frequencies and costs associated with different age groups in netball. The insurance records for all netball claims made during 1999 in Victoria were obtained from the insurer and entered into a database. The overall injury rate was 9.49 injuries per 1000 players, with 829 claims for injuries filed with the insurance company. Of all injuries claimed for, 85.3% were to the lower limb, 8.7% to the upper limb, 3.1% to the spine/torso and 2.9% to the head and face. Lower limb injuries accounted for 85.4% of costs, upper limb injuries 10.7% and head/neck/torso injuries 3.9% of total injury costs. Knee injuries accounted for 56.9% of total costs, with ankle and calf/Achilles injuries costing 12.7 and 11.8% of total costs, respectively. Injury prevention strategies should therefore be directed to three main injuries taking into account costs and incidence. These injuries were: ankle sprains, knee ligament sprains and Achilles tendon strains. Specifically, the prevention program for Achilles injuries should be directed to the >25 years age groups.

Soleus aponeurosis strain distribution following chronic unloading in humans: an in vivo MR phase-contrast study

The in vivo strain properties of human skeletal muscle-tendon complexes are poorly understood, particularly following chronic periods of reduced load bearing. We studied eight healthy volunteers who underwent 4 wk of unilateral lower limb suspension (ULLS) to induce chronic unloading. Before and after the ULLS, maximum isometric ankle plantar flexion torque was determined by using a magnetic resonance (MR)-compatible dynamometry. Volumes of the triceps surae muscles and strain distribution of the soleus aponeurosis and the Achilles tendon at a constant submaximal plantar flexion (20% pre-maximal voluntary contraction) were measured by using MRI and velocity-encoded, phase-contrast MRI techniques. Following ULLS, volumes of the soleus and the medial gastrocnemius and the maximum isometric ankle plantar flexion (maximum voluntary contraction) decreased by 5.5+/-1.9, 7.5+/-2.7, and 48.1+/-6.1%, respectively. The strain of the aponeurosis along the length of the muscle before the ULLS was 0.3+/-0.3%, ranging from -1.5 to 2.7% in different locations of the aponeurosis. Following ULLS, the mean strain was -6.4+/-0.3%, ranging from -1.6 to 1.3%. The strain distribution of the midregion of the aponeurosis was significantly influenced by the ULLS, whereas the more distal component showed no consistent changes. Achilles tendon strain was not affected by the ULLS. These results raise the issue as to whether these changes in strain distribution affect the functional properties of the triceps surae and whether the probability of strain injuries within the triceps surae increases following chronic unloading in those regions of this muscle complex in which unusual strains occur.

In vivo sonometry measurement of strain in the human achilles tendon

A complex response of the trunk muscles occurs to restore equilibrium in response to movement of the support surface. Intra-abdominal pressure (IAP) is considered to contribute to control of the trunk. This study investigated the contribution of IAP to the postural response to multidirection support-surface translation. IAP was recorded with a thin-film pressure transducer inserted via the nose into the stomach and trunk motion was recorded with an optoelectronic system with markers over the spinous process of L1. A pattern of trunk movement was recorded in response to the support-surface translations that was consistent with a ‘hip’ strategy of postural control. The trunk moved in a manner appropriate to move the centre of gravity over the new base of support. IAP was increased with movement in each direction, but varied in timing and amplitude between translation directions. In general, the IAP was greater with translations in the sagittal plane compared to the frontal plane and was initiated earlier for translations in the backward direction. These data indicate that IAP contributes to the postural response associated with support-surface translation and suggest that this is consistent with stiffening the spine.

In vivo mechanical properties of the human Achilles tendon during one-legged hopping

Compliant tendons act as energy stores, which benefit the energetics and power output of a muscle-tendon unit. However the compliance of tendon and the material properties may vary between individuals and hence alter the energy storing capacity of the tendon. We aimed to determine the in vivo Achilles tendon (AT) stress and strain during one-legged hopping and hence the contribution of elastic recoil to mechanical energy changes. We simultaneously measured the length of the Achilles tendon from the muscle-tendon junction to the insertion on the calcaneous and the approximate AT force in ten male participants. The position of the muscle-tendon junction was determined using ultrasound images that were projected into three-dimensional space. Achilles tendon force was measured using inverse dynamics. The results demonstrated that one-legged hopping elicited high tendon strains and that the force-length relationship of the whole tendon is relatively linear, particularly at high strains. The stiffness, elastic modulus and hysteresis varied across the population (inter-quartile range of 145-231 N mm-1, 0.67-1.07 GPa and 17-35%, respectively). These values are within the reported biological range. An average of 38 J of energy was recovered from the elastic recoil of the tendon, which contributes 16% of the total average mechanical work of the hop (254 J). The high strains measured here (average peak strain was 8.3%) and in other studies may be possible due to the complex architecture of the Achilles tendon; however, prolonged hopping may well cause tendon damage. In conclusion, the properties of the elastic Achilles tendon can contribute significantly to the total mechanical work of the body during one-legged hopping; however, individual variation in the properties of the tendon vary the energy storing capacity of this structure.

Comparison of Elasticity of Human Tendon and Aponeurosis in Knee Extensors and Ankle Plantar Flexors in Vivo

The purposes of this study were to compare the elasticity of tendon and aponeurosis in human knee extensors and ankle plantar flexors in vivo and to examine whether the maximal strain of tendon was correlated to that of aponeurosis. The elongation of tendon and aponeurosis during isometric knee extension (n = 23) and ankle plantar flexion (n = 22), respectively, were determined using a real-time ultrasonic apparatus, while the participants performed ramp isometric contractions up to voluntary maximum. To calculate the strain values from the measured elongation, we measured the respective length of tendon and aponeurosis. For the knee extensors, the maximal strain of aponeurosis (12.1 +/- 2.8 %) was significantly greater than that of the patella tendon (8.3 +/- 2.4 %), p < 0.001. On the contrary, the maximal strain of Achilles tendon (5.9 +/- 1.4 %) was significantly greater than that of aponeurosis in ankle plantar flexors (2.7 +/- 1.4 %), p < 0.001. Furthermore, for both knee extensors and ankle plantar flexors there was no significant correlation between maximal strain of tendon and aponeurosis. These results would be important for understanding the different roles of tendon and aponeurosis during human movements and for more accurate muscle modeling.

Nonuniform strain of human soleus aponeurosis-tendon complex during submaximal voluntary contractions in vivo.

The distribution of strain along the soleus aponeurosis tendon was examined during voluntary contractions in vivo. Eight subjects performed cyclic isometric contractions (20 and 40% of maximal voluntary contraction). Displacement and strain in the apparent Achilles tendon and in the aponeurosis were calculated from cine phase-contrast magnetic resonance images acquired with a field of view of 32 cm. The apparent Achilles tendon lengthened 2.8 and 4.7% in 20 and 40% maximal voluntary contraction, respectively. The midregion of the aponeurosis, below the gastrocnemius insertion, lengthened 1.2 and 2.2%, but the distal aponeurosis shortened 2.1 and 2.5%, respectively. There was considerable variation in the three-dimensional anatomy of the aponeurosis and muscle-tendon junction. We suggest that the nonuniformity in aponeurosis strain within an individual was due to the presence of active and passive motor units along the length of the muscle, causing variable force along the measurement site. Force transmission along intrasoleus connective tissue may also be a significant source of nonuniform strain in the aponeurosis.

Effects of Achilles Tendon Path Change on the Myotendinous Junction Movement of the Gastrocnemius Muscle

The effects of the Achilles tendon path change due to muscle contraction on the displacement of the myotendinous junction were determined in the human in vivo. Seven male subjects, whose knees were extended and ankles flexed at a right angle, performed isometric plantar flexion while the Achilles tendon length within the predetermined area (from the point of the myotendinous junction at rest to the calcaneus) was estimated using a high-speed camera and ultrasound apparatus. The Achilles tendon length within the predetermined area decreased by ∼1% at maximal voluntary contraction compared to the relaxed condition, which suggests that the Achilles tendon path change due to isometric contractions moves the myotendinous junction proximally by ∼1%, at the most, of the Achilles tendon length. If we simply calculate the Achilles tendon strain based on the displacement of the myotendinous junction as in previous studies, we would therefore overestimate the strain by ∼1%. This suggests that the tendon path change should be taken into account when tendon strain is calculated from myotendinous junction movements.

The Influence of Heal Lift Manipulation on Sagittal Plane Kinematics in Running

In this study sagittal plane joint angles of the lower extremity were used to obtain an indication of the influence of heel lift manipulation on Achilles tendon strain in running. The influence of increased heel lift on lower extremity kinematics was investigated for 8 heel striking subjects. With increased heel lift, all subjects demonstrated reductions in peak ankle dorsi-flexion and consistent values of peak knee flexion, indicating that there were reductions in peak Achilles tendon strain. Group analysis demonstrated that the reductions in peak ankle angle were statistically significant (p &lt; .01). Typically, subjects also demonstrated adjustments in initial ankle angle, whereby the amount of ankle dorsi-flexion at initial ground contact was reduced with increased heel lift. Group mean data indicated that a 15-mm heel lift resulted in a mean decrease in initial ankle dorsi-flexion of 3.9°, while peak ankle dorsi-flexion was also reduced by 3.9°. It is suggested that the initial ankle angle adjustment acted to maintain a similar range of ankle joint movement in the period from initial ground contact to peak ankle dorsi-flexion across heel lift conditions. The distinct behavior of one subject, who demonstrated an increased ankle dorsi-flexion at ground impact, has highlighted the importance of considering single subject results in studies of footwear variation in running.