Dataset Information

The 3D in vivo Achilles' tendon moment arm, quantified during active muscle control and compared across sexes.

ABSTRACT: The Achilles' tendon moment arm (ATma) is a critical quantity in that it defines the triceps surae's ability to generate a moment on the calcaneus, which is then transferred to the foot. This measure has been primarily acquired two-dimensionally in small male populations. Thus, the primary purpose of this study was to establish the first in vivo three-dimensional measures of the ATma, measured non-invasively during dynamic activity in a large normative population, inclusive of both males and female subjects (n=20). Subjects were each placed supine in a 1.5 T MRI and asked to repeat a simulated toe-raise while a full sagittal-cine-phase contrast (dynamic) MRI dataset was acquired. From these data, the 3D and 2D ATma was calculated. The ATma was scaled by the distal tibial width, based on a correlation analysis. The 2D ATma overestimated its 3D counterpart by 3.1 mm, on average. The scaled ATma was no different between the male and female cohorts, but the scaled Achilles' tendon area was smaller in the male cohort. The magnitudes of the ATma were most similar to previously reported values when variations in ankle angle were taken into account. The results of this study have important implications for the applicability of ATma data to both clinical questions and modeling. Any future studies should adapt the ATma based on subject size and/or sex, ensure compatibility between the manner in which the ankle angle is defined and the data being used, and account for the influence that muscle force has on the 3D ATma.

SUBMITTER: Sheehan FT

PROVIDER: S-EPMC3243112 | biostudies-literature | 2012 Jan

REPOSITORIES: biostudies-literature

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The 3D in vivo Achilles' tendon moment arm, quantified during active muscle control and compared across sexes.

Sheehan Frances T FT

Journal of biomechanics 20111203 2

The Achilles' tendon moment arm (ATma) is a critical quantity in that it defines the triceps surae's ability to generate a moment on the calcaneus, which is then transferred to the foot. This measure has been primarily acquired two-dimensionally in small male populations. Thus, the primary purpose of this study was to establish the first in vivo three-dimensional measures of the ATma, measured non-invasively during dynamic activity in a large normative population, inclusive of both males and fem ...[more]

PMID: 22138193

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Project description: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.

Project description:Vertebrate musculoskeletal locomotion is realized through lever-arm systems. The instantaneous muscle moment arm (IMMA), which is expected to be under selective pressure and thus of interest for ecomorphological studies, is a key aspect of these systems. The IMMA changes with joint motion. It's length change is technically difficult to acquire and has not been compared in a larger phylogenetic ecomorphological framework, yet. Usually, proxies such as osteological in-levers are used instead. We used 18 species of the ecologically diverse clade of caviomorph rodents to test whether its diversity is reflected in the IMMA of the hip extensor M. gluteus medius. A large IMMA is beneficial for torque generation; a small IMMA facilitates fast joint excursion. We expected large IMMAs in scansorial species, small IMMAs in fossorial species, and somewhat intermediate IMMAs in cursorial species, depending on the relative importance of acceleration and joint angular velocity. We modeled the IMMA over the entire range of possible hip extensions and applied macroevolutionary model comparison to selected joint poses. We also obtained the osteological in-lever of the M. gluteus medius to compare it to the IMMA. At little hip extension, the IMMA was largest on average in scansorial species, while the other two lifestyles were similar. We interpret this as an emphasized need for increased hip joint torque when climbing on inclines, especially in a crouched posture. Cursorial species might benefit from fast joint excursion, but their similarity with the fossorial species is difficult to interpret and could hint at ecological similarities. At larger extension angles, cursorial species displayed the second-largest IMMAs after scansorial species. The larger IMMA optimum results in powerful hip extension which coincides with forward acceleration at late stance beneficial for climbing, jumping, and escaping predators. This might be less relevant for a fossorial lifestyle. The results of the in-lever only matched the IMMA results of larger hip extension angles, suggesting that the modeling of the IMMA provides more nuanced insights into adaptations of musculoskeletal lever-arm systems than this osteological proxy.

Dataset Information

The 3D in vivo Achilles' tendon moment arm, quantified during active muscle control and compared across sexes.

Publications

The 3D in vivo Achilles' tendon moment arm, quantified during active muscle control and compared across sexes.

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