Moment arms about the ankle joint

NewsBot · Apr 12, 2011

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Moment Arms of the Ankle Throughout the Range of Motion in Three Planes
McCullough MB, Ringleb SI, Arai K, Kitaoka HB, Kaufman KR
Foot Ankle Int. 2011 Mar;32(3):300-306

BACKGROUND: The moment, a force applied at a distance, is responsible for movement and balance. A key component of the moment is the moment arm. The moment arms of nine muscles surrounding the ankle complex during motion in three planes, were studied.

MATERIALS AND METHODS: Five cadaveric feet were mounted in a testing device that created moments in the sagittal, coronal and transverse planes. Axial and tendon loads were applied as the foot was passively moved in these planes. Tendon excursions and bone kinematics were monitored. The moment arm was calculated using the tendon excursion method and averaged across all specimens.

RESULTS: The largest average moment arm during plantarflexion/dorsiflexion, was the Achilles (mean, 53.1; SD, 5.1 mm). During internal/external rotation the largest moment arm was the peroneus brevis (mean, 20.5; SD, 6.4 mm). During inversion/eversion, the largest moment arm was the peroneus longus (31 mm; SD, 2.3 mm).

CONCLUSION: This study quantified the functional moment arms of nine tendons of the ankle/foot. The involvement of multiple tendons in multiple planes of motion should be considered in computational models and when deciding treatments.

CLINICAL RELEVANCE: The correlation between moment arms and muscle function has significant effects on treatment efficacy. Information on the balance of moments around the ankle will assist in achieving optimal biomechanical behavior following operative treatments.
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efuller · Apr 12, 2011

NewsBot said: ↑

Moment Arms of the Ankle Throughout the Range of Motion in Three Planes
McCullough MB, Ringleb SI, Arai K, Kitaoka HB, Kaufman KR
Foot Ankle Int. 2011 Mar;32(3):300-306

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Anyone have a copy of the paper? It would support my contention, in the anterior tibial thread, that the posterior tibial tendon has very very little moment arm at the ankle joint.

Eric

davsur08 · Apr 14, 2011

Dr.Fuller

as you requested

Regards

David

Petcu Daniel · Apr 21, 2011

Hello,
Which are the relevance of this study from the perspective of subtalar joint rotational equilibrium as in the rotation axis considered were medial-lateral, anterior-posterior and inferior-superior ?
Thanks,
Daniel

efuller · Apr 21, 2011

Petcu Daniel said: ↑

Hello,
Which are the relevance of this study from the perspective of subtalar joint rotational equilibrium as in the rotation axis considered were medial-lateral, anterior-posterior and inferior-superior ?
Thanks,
Daniel
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The subtalar joint has the least amount of motion in the sagittal plane. The average inclination of the axis will have approximately equal amounts of motion in the transverse and frontal planes. If you look at the graphs of moment arm for the Achilles tendon, you can see that it had a very small moment arm in the coronal (transverse) and the frontal planes and a very large moment arm in the sagittal plane. This is consistent with what we thought before that the Achilles is primarily and ankle plantar flexor and can have a variable effect at the STJ.

The graphs also show that the post tib also has the smallest lever arm of any muscle in the sagittal plane, so it would be a very poor plantar flexor of the ankle. That fact was relevant in a different thread that I wish I could remember the name of.

Eric

mike weber · Apr 21, 2011

efuller said: ↑

The subtalar joint has the least amount of motion in the sagittal plane. The average inclination of the axis will have approximately equal amounts of motion in the transverse and frontal planes. If you look at the graphs of moment arm for the Achilles tendon, you can see that it had a very small moment arm in the coronal (transverse) and the frontal planes and a very large moment arm in the sagittal plane. This is consistent with what we thought before that the Achilles is primarily and ankle plantar flexor and can have a variable effect at the STJ.

The graphs also show that the post tib also has the smallest lever arm of any muscle in the sagittal plane, so it would be a very poor plantar flexor of the ankle. That fact was relevant in a different thread that I wish I could remember the name of.

Eric
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I think it is this one - How significant is the Peroneus longus as a Plantarflexor of the 1st Ray?

NewsBot · Feb 10, 2015

Achilles tendon moment arms: The importance of measuring at constant tendon load when using the tendon excursion method
Katarzyna Olszewski, Taylor J.M. Dick, James M. Wakeling
Jnl Biomech; Article in Press

Achilles tendon moment arms are commonly measured using the tendon-excursion technique and ultrasound imaging of the muscle-tendon junction. The tendon-excursion technique relies on the assumption that the tendon load is constant and thus it does not stretch. However, previous studies have not enforced this constraint and thus it is not known how sensitive the estimated Achilles tendon moment arms are to varying load during the measurement process. The aim of this study was to compare estimates of Achilles tendon moment arms when calculated using the different constraints of constant force (and thus tendon stretch), constant joint torque, or contraction effort. Achilles tendon moment arms were measured for the medial and lateral gastrocnemii in 8 healthy male subjects across five different ankle angles (−5° dorsiflexion to 35° plantarflexion), and a range of contraction levels. Moment arms were calculated for three different constraints of constant force, torque, or effort. Moment arms were significantly greater for the lateral gastrocnemius than for the medial gastrocnemius. At low contraction levels, including the passive condition, the moment arms increased with plantarflexion, whereas the moment arms decreased with plantarflexion at higher contraction levels. There was no difference between the calculated moment arms using the constant force and the constant torque methods, however both these methods yielded significantly different moment arms when compared to the commonly used constant effort method.
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NewsBot · Oct 11, 2016

Comparison of the Achilles tendon moment arms determined using the tendon excursion and three‐dimensional methods
Satoru Hashizume, Atsuki Fukutani, Kazuki Kusumoto, Toshiyuki Kurihara, Toshio Yanagiya
Physiological Reports Published 5 October 2016 Vol. 4 no. e12967 DOI: 10.14814/phy2.12967

The moment arm of muscle‐tendon force is a key parameter for calculating muscle and tendon properties. The tendon excursion method was used for determining the Achilles tendon moment arm (ATMA). However, the accuracy of this method remains unclear. This study aimed to investigate the magnitude of error introduced in determining the ATMA using the tendon excursion method by comparing it with the reference three‐dimensional (3D) method. The tendon excursion method determined the ATMA as the ratio between the Achilles tendon displacement during foot rotation from 15° of dorsiflexion to 15° of plantarflexion and the joint rotation angle. A series of foot images was obtained at 15° of dorsiflexion, the neutral position, and 15° of plantarflexion. The 3D value of the ATMA was determined as the shortest distance between the talocrural joint axis and the line of action of the Achilles tendon force. The ATMA determined by the tendon excursion method was smaller by 3.8 mm than that determined using the 3D method. This error may be explained mainly by the length change in the Achilles tendon due to the change in the force applied to it, as passive plantarflexion torque was different by 11 Nm between 15° of dorsiflexion and 15° of plantarflexion. Furthermore, the ATMAs determined using the 3D and tendon excursion methods were significantly correlated but the coefficient of determination was not large (R2 = 0.352). This result suggests that the tendon excursion method may not be feasible to evaluate the individual variability of the ATMA.
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NewsBot · Jan 13, 2017

Reliability of Achilles Tendon Moment Arm Measured In Vivo Using Freehand Three-Dimensional Ultrasound
Steven J. Obst et al
Journal of Applied Biomechanics; Ahead of Print

This study investigated reliability of freehand three-dimensional ultrasound (3DUS) measurement of in vivo human Achilles tendon (AT) moment arm. Sixteen healthy adults were scanned on two separate occasions by a single investigator. 3DUS scans were performed over the free AT, medial malleolus and lateral malleolus with the ankle passively positioned in maximal dorsiflexion, mid dorsiflexion, neutral, mid plantar flexion and maximal plantar flexion. 3D reconstructions of the AT, medial malleolus and lateral malleolus were created from manual segmentation of the ultrasound images and used to geometrically determine the AT moment arm using both a straight (straight ATMA) and curved (curved ATMA) tendon line-of-action. Both methods were reliable within and between-session (intra-class correlation coefficients >0.92; coefficient of variation <2.5 %) and revealed that AT moment arm increased by ~7 mm from maximal dorsiflexion (~41mm) to maximal plantar flexion (~48 mm). Failing to account for tendon curvature led to a small overestimation (<2 mm) of AT moment arm that was most pronounced in ankle plantar flexion, but was less than the minimal detectable change of the method and could be disregarded.
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NewsBot · Feb 14, 2017

Variation in the human Achilles tendon moment arm during walking.
Rasske K, Thelen DG, Franz JR.
Comput Methods Biomech Biomed Engin. 2017 Feb;20(2):201-205

The Achilles tendon (AT) moment arm is an important determinant of ankle moment and power generation during locomotion. Load and depth-dependent variations in the AT moment arm are generally not considered, but may be relevant given the complex triceps surae architecture. We coupled motion analysis and ultrasound imaging to characterize AT moment arms during walking in 10 subjects. Muscle loading during push-off amplified the AT moment arm by 10% relative to heel strike. AT moment arms also varied by 14% over the tendon thickness. In walking, AT moment arms are not strictly dependent on kinematics, but exhibit important load and spatial dependencies.
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NewsBot · Feb 17, 2017

A simple but reliable method for measuring 3D Achilles tendon moment arm geometry from a single, static magnetic resonance scan
C.F. Alexander et al
Journal of Biomechanics; February 16, 2017

Current methods for measuring in-vivo 3D muscle-tendon moment arms generally rely on the acquisition of magnetic resonance scans at multiple joint angles. However, for patients with musculoskeletal pathologies such as fixed contractures, moving a joint through its full range of motion is not always feasible. The purpose of this research was to develop a simple, but reliable in-vivo 3D Achilles tendon moment arm (ATMA) technique from a single static magnetic resonance image (MRI) scan. To accomplish this, for nine healthy adults (5 males, 4 females), the geometry of a cylinder was fit to the 3D form of the talus dome, which was used to estimate the talocrural flexion/extension axis, and a fifth-order polynomial fit to the line of action of the Achilles tendon. The single static scan in-vivo 3D Achilles tendon moment arm estimates were compared to estimates obtained from the same subjects at the same ankle joint angles using a previously validated 3D dynamic MRI based in-vivo ATMA measurement technique. The ATMA estimates from the single scan in-vivo 3D method (52.5mm ±5.6) were in excellent agreement (ICC = 0.912) to the validated in-vivo 3D method (51.5mm±5.1). These data show reliable in-vivo 3D ATMA can be obtained from a single MRI scan for healthy adult populations. The single scan, in-vivo 3D ATMA technique provides researchers with a simple, but reliable method for obtaining subject-specific ATMAs for musculoskeletal modelling purposes.
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NewsBot · Mar 22, 2017

Achilles tendon moment arm length is smaller in children with cerebral palsy than in typically developing children.
Kalkman BM et al
J Biomech. 2017 Mar 3. pii: S0021-9290(17)30128-8. doi: 10.1016/j.jbiomech.2017.02.027

When studying muscle and whole-body function in children with cerebral palsy (CP), knowledge about both internal and external moment arms is essential since they determine the mechanical advantage of a muscle over an external force. Here we asked if Achilles tendon moment arm (MAAT) length is different in children with CP and age-matched typically developing (TD) children, and if MAAT can be predicted from anthropometric measurements. Sixteen children with CP (age: 10y 7m±3y, 7 hemiplegia, 12 diplegia, GMFCS level: I (11) and II (8)) and twenty TD children (age: 10y 6m±3y) participated in this case-control study. MAAT was calculated at 20° plantarflexion by differentiating calcaneus displacement with respect to ankle angle. Seven anthropometric variables were measured and related to MAAT. We found normalized MAAT to be 15% (∼7mm) smaller in children with CP compared to TD children (p=0.003). MAAT could be predicted by all anthropometric measurements with tibia length explaining 79% and 72% of variance in children with CP and TD children, respectively. Our findings have important implications for clinical decision making since MAAT influences the mechanical advantage about the ankle, which contributes to movement function and is manipulated surgically.
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NewsBot · Mar 24, 2017

Musculoskeletal modelling of human ankle complex: Estimation of ankle joint moments
Prashant K. Jamwal et al
Clinical Biomechanics; Article in Press

Highlights
•Musculoskeletal model of the ankle complex considering the biaxial structure
•Model provides estimates of overall mechanical characteristics.
•Considerations of forces applied along ligaments and muscle-tendon units.
•Validation of the ankle model by comparing its outputs published literature
•Validation with experimental data from a parallel ankle rehabilitation robot
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Background
A musculoskeletal model for the ankle complex is vital in order to enhance the understanding of neuro-mechanical control of ankle motions, diagnose ankle disorders and assess subsequent treatments. Motions at the human ankle and foot, however, are complex due to simultaneous movements at the two joints namely, the ankle joint and the subtalar joint. The musculoskeletal elements at the ankle complex, such as ligaments, muscles and tendons, have intricate arrangements and exhibit transient and nonlinear behaviour.

Methods
This paper develops a musculoskeletal model of the ankle complex considering the biaxial ankle structure. The model provides estimates of overall mechanical characteristics (motion and moments) of ankle complex through consideration of forces applied along ligaments and muscle-tendon units. The dynamics of the ankle complex and its surrounding ligaments and muscle-tendon units is modelled and formulated into a state space model to facilitate simulations. A graphical user interface is also developed during this research in order to include the visual anatomical information by converting it to quantitative information on coordinates.

Findings
Validation of the ankle model was carried out by comparing its outputs with those published in literature as well as with experimental data obtained from an existing parallel ankle rehabilitation robot.

Interpretation
Qualitative agreement was observed between the model and measured data for both, the passive and active ankle motions during trials in terms of displacements and moments.
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NewsBot · Jun 29, 2017

Relationship between Achilles tendon length and running performance in well-trained male endurance runners
Hiromasa Ueno, et al
Scandinavian Journal of Medicine & Science in Sports; 28 June 2017

The present study aimed to determine the relationship between Achilles tendon (AT) length and running performance, including running economy, in well-trained endurance runners. We also examined the reasonable portion of the AT related to running performance among AT lengths measured in three different portions. The AT lengths at three portions and cross-sectional area (CSA) of 30 endurance runners were measured using magnetic resonance imaging. Each AT length was calculated as the distance from the calcaneal tuberosity to the muscle-tendon junction of the soleus, gastrocnemius medialis (GMAT), and gastrocnemius lateralis, respectively. These AT lengths were normalized with shank length. The AT CSA was calculated as the average of 10 mm, 20 mm, and 30 mm above the distal insertion of the AT, and normalized with body weight. Running economy was evaluated by measuring energy cost during three 4-min submaximal treadmill running trials at 14, 16, and 18 km/h, respectively. Among three AT lengths, only a GMAT correlated significantly with personal best 5000-m race time (r = -0.376, P = 0.046). Furthermore, GMAT correlated significantly with energy cost during submaximal treadmill running trials at 14 km/h and 18 km/h (r = -0.446 and -0.429, respectively, P < 0.05 for both), and a trend towards such significance was observed at 16 km/h (r = -0.360, P = 0.050). In contrast, there was no correlation between AT CSA and running performance. These findings suggest that longer AT, especially GMAT, may be advantageous to achieve superior running performance, with better running economy, in endurance runners.
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NewsBot · Jan 24, 2018

Estimates of Achilles Tendon Moment Arm Length at Different Ankle Joint Angles: Effect of Passive Moment
Jared R. Fletcher, Brian R. MacIntosh
Journal of Applied Biomechanics; Ahead of print

The length of a muscle’s moment arm can be estimated non-invasively using ultrasound, and the tendon excursion method. The main assumption with the tendon excursion method, however, is that the force acting on the tendon during passive rotation is constant. However, passive force changes through the range of motion, and moment arm is underestimated. We attempted to account for passive force on the measurement of Achilles tendon moment arm using the tendon excursion method in 8 male and female runners. Tendon excursion was measured using ultrasound while the ankle was passively rotated at 0.17 rad•s-1. Moment arm was calculated at 5° intervals as the ratio of tendon displacement to joint rotation from 70° to 115°. Passive moment (MP) was measured by a dynamometer. The displacement attributable to MP was calculated by monitoring tendon displacement during a ramp isometric maximum contraction. MP was 5.7±2.1 Nm at 70° and decreased exponentially from 70°-90°. °. This resulted in MP-corrected moment arms that were significantly larger than uncorrected moment arms at joint angles where MP was present. Further, MP-corrected moment arms did not change with ankle angle, which was not the case for uncorrected moment arms.
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NewsBot · Feb 13, 2018

The geometrical axis of the talocrural joint suggestions for a new measurement of the talocrural joint axis
Leif Claassen et al
FAS; Article in Press

Highlights
•Study shows a system for estimating the geometrical talocrural joint axis.
•High number of 98 CT scans analyzed.
•High interindividual variations highlight the potential need of patient specific implantation techniques for Total Ankle Replacement.
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Background
Despite intensive research there is no consensus about the talocrural joint axis. The aim of the present study is a new method to determinate the geometric rotational axis of the talocrural joint.

Methods
We analyzed 98 CT-scans of full cadaver Caucasian legs. We generated three-dimensional reconstruction models of the talus. A best fitting cone was orientated to the talar articular surface. The geometric rotational axis was defined to be the axis of this cone.

Results
The geometric rotational axis of the talocrural joint is orientated from lateral-distal to medial-proximal (85.6° ± 10 compared to anatomical tibial axis in torsional plane), from posterior-distal to anterior-proximal (81.43° ± 44.35 compared to anatomical tibial axis in sagittal plane) and from posterior-medial to anterior-lateral (169.2° ± 5.91 compared to intermalleolar axis in axial plane).

Conclusion
The consideration of our results might be helpful for better understanding of ankle biomechanics.
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NewsBot · Jun 30, 2018

Aging effects on the Achilles tendon moment arm during walking.
Rasske K, Franz JR
J Biomech. 2018 Jun 18.

The Achilles tendon (AT) moment arm transforms triceps surae muscle forces into a moment about the ankle which is critical for functional activities like walking. Moreover, the AT moment arm changes continuously during walking, as it depends on both ankle joint rotation and triceps surae muscle loading (presumably due to bulging of the muscle belly). Here, we posit that aging negatively effects the architecturally complex AT moment arm during walking, which thereby contributes to well-documented reductions in ankle moment generation during push-off. We used motion capture-guided ultrasound imaging to quantify instantaneous variations in the AT moment arms of young (23.9 ± 4.3 years) and older (69.9 ± 2.6 years) adults during walking, their dependence on triceps surae muscle loading, and their association with ankle moment generation during push-off. Older adults walked with 11% smaller AT moment arms and 11% smaller peak ankle moments during push-off than young adults. Moreover, as hypothesized, these unfavourable changes were significantly and positively correlated (r2 = 0.38, p < 0.01). More surprisingly, aging attenuated load-dependent increases in the AT moment arm (i.e., those between heel-strike and push-off at the same ankle angle); only young adults exhibited a significant increase in their AT moment arm due to triceps surae muscle-loading. Age-associated reductions in triceps surae volume or activation, and thus muscle bulging during force generation, may compromise the mechanical advantage of the AT during the critical push-off phase of walking in older adults. Thus, strategies to restore and/or improve locomotor performance in our aging population should consider these functionally important changes in musculoskeletal behavior.
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NewsBot · Oct 3, 2018

The Effect of Three Foot Types on the Achilles Tendon Lever Arm
Manja Deforth, MSc, Lukas Zwicky, MSc, Tamara Horn Lang, PhD, Beat Hintermann, MD
AOFAS Annual Meeting 2018 1

Introduction/Purpose: During locomotion, propulsion of the body is created by the force of the triceps surae complex as it is
transmitted to the metatarsal heads. The amount and pattern of the resulting propulsion force highly depends on the moment arm
of the Achilles tendon. To our knowledge, no data exists on how and to which extent position and morphology of the foot affects
the moment arm of the Achilles tendon. The aim of this study was 1) to develop a method to determine the Achilles tendon
moment arm, and 2) to calculate the Achilles tendon moment arm with the foot in different degrees of dorsi- and plantarflexion
for 3 foot types (normal arched foot, pes planus, and pes cavus).
Methods: 99 study participants with a healthy ankle joint (males, 40; females, 59; mean age 49 [range, 14 – 78] years) were
included. Participants’ foot type was classified as a normal arched foot (n = 33), as pes planus (n = 33), or as pes cavus (n = 33)
based on the calcaneal inclination angle (CI) (Figure 1). Besides the foot type, the foot length (FL), the calcaneal insertion of the
Achilles tendon (ATI), the angle (a) between the line (L) connecting ATI with the center of rotation of the ankle (COR) and the
horizontal line (L’) were measured on the lateral radiographs. The interrater reliabilities of measuring a on radiographs and on
MRIs were compared. The lever arm of the Achilles tendon (L’calculated) was calculated as following (foot and tibia were
regarded as two rigid segments; the influences of other muscles were neglected):
L'calculated = cos(a - plantarflexion)*L
Results: The interrater reliability of a was higher on radiographs (ICC = 0.84, [0.73 – 0.91]) than on MRIs (ICC = 0.61, [0.27 –
0.81]). The ICC comparing a measured on MRIs and radiographs was 0.63 [0.50-0.74]. There was no difference in FL between the
three foot types (p = 0.199). However, the average a was significantly different (normal arched foot 31°, pes planus 24°, pes cavus
36°, p = 0.021), resulting in a statistically significant shorter Achilles tendon lever arm for pes cavus than for pes planus (p <
0.0001) and normal arched feet (p = 0.006) in neutral position. The maximum lever arm for the three different foot types was
reached at different degrees of plantarflexion (Figure 2).
Conclusion: The assessment of the Achilles tendon lever arm using radiographs is reliable. The foot configuration determines the
lever arm of the Achilles tendon for a given flexion position of the foot. It also determines the plantarflexion position where the
Achilles tendon reaches the maximum of its lever arm. This has to be taken into consideration when planning surgeries that
change a or L, as they may also result in changes of plantarflexion power.
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NewsBot · Oct 14, 2018

The Effect of Foot Type on the Achilles Tendon Moment Arm and Biomechanics
ManjaDeforthLukasZwickyTamaraHornBeatHintermann
The Foot; 9 October 2018

Highlights
•The average Achilles tendon moment arm was shorter for pes cavus than pes planus.
•The maximum Achilles tendon moment arm was found at different plantarflexion.
•The interrater reliability of alpha was higher on radiographs than on MRIs.
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Background
The aim was to calculate the Achilles tendon moment arm in different degrees of plantarflexion for pes planus, pes cavus and normal arched feet.

Methods
99 patients (99 radiographs; 40 males, 59 females; mean age 49 years, SD 15) with a healthy ankle joint and a preoperative weightbearing lateral radiograph of the foot were included. Three groups (pes planus, pes cavus and normal-arched feet) with equal sample sizes (n = 33) were formed. On radiographs, the angle formed between a horizontal line and the line connecting the insertion of the Achilles tendon with the center of rotation of the ankle, was measured. The interrater reliabilities (ICC) of the angle alpha were compared on radiographs and on MRIs. Using the angle alpha, the Achilles tendon moment arm was calculated in different plantarflexion positions.

Results
The ICC of alpha was higher on radiographs (.84, [.73–.91]) than on MRIs (.61, [.27–.81]). The average alpha was statistically significantly different (normal arched foot 31 degrees, pes planus 24 degrees, pes cavus 36 degrees, p = .021), resulting in a significant shorter Achilles tendon moment arm for pes cavus than for pes planus (p < .0001) and normal arched feet (p = .006) in neutral position.

Conclusion
Our data suggests that it is feasible to use radiographs to measure the Achilles tendon moment arm. The maximum Achilles tendon moment arm is reached at different angles of ankle flexion for pes cavus, pes planus and normal-arched feet. This has to be taken into consideration when planning surgeries.
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NewsBot · Jan 12, 2020

Ankle Control in Walking and Running: Speed- and Gait-related Changes in Dynamic Mean Ankle Moment Arm (DMAMA).
Adamczyk PG
J Biomech Eng. 2019 Dec 1

The human foot-ankle complex uses heel-to-toe ground contact progression in walking, but primarily forefoot contact in high-speed running. This qualitative change in ankle control is clear to the runner, but current measures of ankle behavior cannot isolate the effect, and it is unknown how it changes across moderate speeds. We investigated this dynamic ankle control across a range of walking and running speeds using a new measure, the Dynamic Mean Ankle Moment Arm (DMAMA): the ratio of sagittal ankle moment impulse to ground reaction force impulse on a single limb. We hypothesized that DMAMA would increase with speed in both walking and running, indicating more forefoot-dominated gait with ground reaction forces more anterior to the ankle. Human subjects walked (1.0 to 2.0 m/s) and ran (2.25 to 5.25 m/s) on an instrumented treadmill with motion capture and pressure insoles to estimate DMAMA. DMAMA decreased with increasing walking speed, then increased upon the transition to running, and increased further with increasing running speed. These results provide quantitative evidence that walking becomes more hindfoot-dominated as speed increases - similar to behavior during acceleration - and that running is more forefoot-dominated than walking. Instantaneous center of pressure at initial ground contact did not follow the same trends. The discrepancy highlights the value of DMAMA in summarizing ankle control across the whole stance phase. DMAMA may provide a useful outcome metric for evaluating biomimetic prostheses and for quantifying foot contact styles in running.
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NewsBot · Jun 10, 2020

Effective Mechanical Advantage About the Ankle Joint and the Effect of Achilles Tendon Curvature During Toe-Walking
Carla Harkness-Armstrong et al
Front Physiol. 2020 May 19;11:407

Aim: To study the causes of locomotor dysfunction, estimate muscle forces, or understand the influence of altered sarcomere and muscle properties and behaviours on whole body function, it is necessary to examine the leverage with which contractile forces operate. At the ankle joint, current methods to quantify this leverage for the plantarflexors do not account for curvature of the Achilles tendon, and so may not be appropriate when studying equinus gait. Thus, novel methodologies need to be developed and implemented to quantify the Achilles tendon moment arm length during locomotion. Methods: Plantarflexor internal moment arm length and effective mechanical advantage of 11 typically developed young adults were calculated throughout stance, while heel-toe walking and voluntarily toe-walking on an instrumented treadmill. Achilles tendon moment arm was defined in two-ways: (1) assuming a straight tendon, defined between the gastrocnemius medialis myotendinous junction and Achilles tendon insertion point, and (2) accounting for tendon curvature, by tracking the initial path of the Achilles tendon from the calcaneal insertion. Results: When accounting for tendon curvature, Achilles tendon moment arm length and plantarflexor effective mechanical advantage did not differ between walking conditions (p > 0.05). In contrast, when assuming a straight tendon, Achilles tendon moment arm length (p = 0.043) and plantarflexor effective mechanical advantage (p = 0.007) were significantly greater when voluntary toe-walking than heel-toe walking in late stance. Discussion: Assuming a straight Achilles tendon led to a greater Achilles tendon moment arm length and plantarflexor effective mechanical advantage during late stance, compared to accounting for tendon curvature. Consequently, plantarflexor muscle force would appear smaller when assuming a straight tendon. This could lead to erroneous interpretations of muscular function and fascicle force-length-velocity behaviour in vivo, and potentially inappropriate and ineffective clinical interventions for equinus gait.
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NewsBot · Aug 19, 2020

Achilles tendon moment arms are similar when computed using a single fixed axis versus a moving instantaneous helical axis
Francesca E Wade et al
J Biomech. 2020 Aug 26;109:109907

Accurate location of the axis of ankle rotation is critical to in vivo estimates of Achilles tendon moment arm. Here we investigated how the plantarflexion moment arm of the Achilles tendon is affected by using an instantaneous helical axis that moves with ankle motion as opposed to a single fixed joint axis that approximates the average axis of rotation. Twenty young healthy adults performed a series of weightbearing cyclical plantar- and dorsi-flexion motions. Motion analysis tracked the motions of markers placed on the foot and shank and also tracked an ultrasound probe imaging the Achilles tendon. Differences in ATma between the methods were investigated using a two-way repeated-measures ANOVA with factors of joint angle (+5°, 0°, -5°, -10°, -15°) and method (instantaneous helical axes, fixed axis). Moment arms computed between the two methods were moderately to strongly correlated, especially in the mid-range of motion (for 0° to 10° plantarflexion, all r2 > 0.619 and all p < 0.004). The two methods produced Achilles tendon moment arms that were comparable and not significantly different except in the most dorsiflexed position, when they differed on average by 9.35 ± 3.23 mm (p = 0.001). Our results suggest that either approach for locating the axis of ankle rotation would be appropriate for the purpose of estimating ATma, but that a fixed axis may be preferable because it is applicable over a greater range of ankle motion.
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NewsBot · Nov 24, 2020

Achilles Tendon Moment Arm Changes with Total Ankle Arthroplasty
Francesca E Wade et al
J Orthop Res. 2020 Nov 22

Prior research on total ankle arthroplasty (TAA) has focused on improvements in pain and function following the surgical treatment of ankle arthritis, but its effect on ankle joint mechanics has received relatively little attention. The plantarflexion moment arm of the Achilles tendon is a critical determinant of ankle function with the potential to be altered by TAA. Here we investigate the effect of TAA on Achilles tendon moment arm assessed using two methods. Standing sagittal-plane radiographs were obtained for ten patients pre- and post-surgery, from which anterior-posterior distance between the posterior calcaneus and the center of the talar dome was measured. Ultrasound imaging and three-dimensional (3D) motion capture were used to obtain moment arm pre- and post-TAA. The absolute changes in moment arm pre- to post-TAA were significantly different from zero for both methods (9.6 mm from ultrasound and 4.6 percent of the calcaneus length from radiographs). Only 46% of the variance in post-operative 3D Achilles tendon moment arm was explained by the pre-operative value (r2 = 0.460; p = 0.031), whilst pre- and post-TAA values from radiographs were not correlated (r2 = 0.192, p = 0.206). While we did not find significant mean differences in Achilles tendon moment arm between pre- and post-TAA, we did find absolute changes in 3D moment arm that were significantly different from zero and these changes were partially explained by a change in location of the talar dome as indicated by measurements from radiographs (r2 = 0.497, p = 0.023).
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NewsBot · Jan 12, 2021

Longer Achilles tendon moment arm results in better running economy
B. Kovács et al
Physiology International

Based on the current literature, the link between Achilles tendon moment arm length and running economy is not well understood. Therefore, the aim of this study was to further investigate the connection between Achilles tendon moment arm and running economy and the influence of Achilles tendon moment arm on the function of the plantarflexor muscle-tendon unit during running.

Ten male competitive marathon runners volunteered for this study. The participants ran on a treadmill at two running speeds: 3 and 3.5 m s−1. During running the oxygen consumption, lower leg kinematics, electrical activity of plantar flexor muscles, and fascicle behavior of the lateral gastrocnemius were measured simultaneously. On the second occasion, an MRI scan of the right leg was taken and used to estimate the Achilles tendon moment arm length.

There was a negative correlation between running economy and the body height normalized moment arm length at both selected speeds (r = −0.68, P = 0.014 and r = −0.70, P = 0.01). In addition, Achilles tendon moment arm length correlated with the amplitude of the ankle flexion at both speeds (r = −0.59, P = 0.03 and r = −0.60, P = 0.03) and with the electrical activity of the medial gastrocnemius muscle at 3 m s−1 speed (r = −0.62, P = 0.02). Our finding supports the concept that a longer moment arm could be beneficial for distance runners.
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NewsBot · May 15, 2023

Does foot anthropometry relate to plantar flexor fascicle mechanics and metabolic energy cost across various walking speeds?
Nikolaos Papachatzis et al
J Exp Biol. 2023 Apr 24

Foot structures define the leverage in which the ankle muscles push off against the ground during locomotion. While prior studies have indicated that inter-individual variations in anthropometry (e.g., heel and hallux lengths) can directly affect force production of ankle plantar flexor muscles, its effect on the metabolic energy cost of locomotion has been inconclusive. Here, we tested the hypotheses that shorter heels and longer halluces are associated with slower plantar flexor (soleus) shortening velocity and greater ankle plantar flexion moment, indicating enhanced force potential due to the force-velocity relationship. We also hypothesized that such anthropometry profiles would reduce the metabolic energy cost of walking at faster walking speeds. Healthy young adults (N=15) walked at three speeds (1.25, 1.75, and 2.00 ms-1), and we collected in-vivo muscle mechanics (via ultrasound), activation (via electromyography), and whole-body metabolic energy cost of transport (via indirect calorimetry). Contrary to our hypotheses, shorter heels and longer halluces were not associated with slower soleus shortening velocity or greater plantar flexion moment. Additionally, longer heels were associated with reduced metabolic cost of transport, but only at the fastest speed (2.00 ms-1, R2=0.305, p=0.033). We also found that individuals with longer heels required less increase in plantar flexor (soleus and gastrocnemius) muscle activation to walk at faster speeds, potentially explaining the reduced metabolic cost
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NewsBot · Nov 14, 2023

A longer Achilles tendon moment arm length is not associated with superior hopping performance
Bálint Kovács et al
Front Bioeng Biotechnol. 2023 Oct 26:11:127016

Variability in musculoskeletal and lower leg structure has the potential to influence hopping height. Achilles tendon moment arm length and plantarflexor muscle strength can influence ankle joint torque development and, consequently, hopping performance. While most studies have examined the connection of the Achilles tendon moment arm with hopping performance including the resting length, in this study we attempted to explore how the changes in Achilles tendon moment arm are related to hopping performance. Therefore, the purpose of this study was to test for correlations between foot and lower leg muscle structure parameters (i.e., muscle mass, volume, cross-sectional area and Achilles tendon moment arm length) and hopping height performance in relation to changes in Achilles tendon moment arm length. Eighteen participants (10 males 8 female) performed repetitive bilateral hopping on a force platform while sagittal plane kinematics of the lower leg were recorded. Additionally, maximal isometric plantarflexion was measured. To obtain structural parameters of the lower leg, the right lower leg of each participant was scanned with magnetic resonance imaging. The cross-sectional areas of the Achilles tendon, soleus, lateral and medial gastrocnemius were measured, while muscle volumes, muscle mass, and Achilles tendon moment arm length were calculated. Contrary to our initial assumption, longer Achilles tendon moment arm did not result in superior hopping performance. Interestingly, neither maximal isometric plantarflexion force nor muscle size correlated with repetitive bilateral hopping performance. We can assume that the mechanical characteristics of the tendon and the effective utilization of the stored strain energy in the tendon may play a more important role in repetitive hopping than the structural parameters of the lower leg.
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