Human Achilles Tendon – in-vivo estimates of the moment arm


This research publication by (now Professor) Costis Maganaris as first author was an important technical analysis which formed part of his PhD thesis which was jointly supervised by Professor Vasilios Baltzopoulos and Professor Anthony J Sargeant

In vivo measurement-based estimations of the human Achilles tendon moment arm

Costis N Maganaris, Vasilios Baltzopoulos, Anthony J Sargeant.

European Journal of Applied Physiology

Eur J Appl Physiol. 2000 Nov;83(4 -5):363-9

The aim of the present study was to estimate and compare in vivo measurement-based Achilles tendon moment arm lengths at rest and during isometric plantarflexion maximum voluntary contraction (MVC) using the centre-of-rotation (COR) and the tendon-excursion (TE) methods. Both methods were based on morphometric analysis of sagittal-plane magnetic resonance images of the foot. Using the COR method, moment arms were obtained at ankle angles from 15 degrees of dorsiflexion to 30 degrees of plantarflexion in steps of 15 degrees, digitizing the perpendicular distance from a moving centre of rotation in the tibio-talar joint to the Achilles tendon action line. The TE method was based on measurement of calcaneal displacement along the tibial axis during 15 degrees rotations of the ankle joint, from 30 degrees of dorsiflexion to 45 degrees of plantarflexion. The two methods gave similar estimations at rest varying from 4.3 to 5.6 cm. Using the COR method, the Achilles tendon moment arm during MVC was larger by 1-1.5 cm (22-27%, P < 0.01) than the respective resting value. In contrast, no difference (P > 0.05) was found between the resting and MVC moment arm estimations of the TE method. The disagreement in moment arms during MVC may be attributed to differences in the assumptions made between the two methods. The TE method has more limitations than the COR method and its estimations during MVC should be treated with caution. Resting Achilles tendon moment arm estimations of the COR method should be multiplied by 1.22-1.27 when maximal isometric plantarflexion joint moments, musculotendon forces and stresses are predicted using modelling

Research into human tendon properties by Costis Maganaris, Vassilios Baltzopolous and Anthony J Sargeant


Changes in Achilles tendon moment arm from rest to maximum isometric plantarflexion: In vivo observations in man

Article (PDF Available)inThe Journal of Physiology 510 ( Pt 3)(3):977-85 · August 1998with85 Reads

DOI: 10.1111/j.1469-7793.1998.977bj.x · Source: PubMed
  • 35.76 · Liverpool John Moores University
  • 38.82 · Liverpool John Moores University
  • 41.33 · VU University Amsterdam
    1. The purpose of the present study was to examine the effect of a plantarflexor maximum voluntary contraction (MVC) on Achilles tendon moment arm length.
    2. Sagittal magnetic resonance (MR) images of the right ankle were taken in six subjects both at rest and during a plantarflexor MVC in the supine position at a knee angle of 90 deg and at ankle angles of -30 deg (dorsiflexed direction), -15 deg, 0 deg (neutral ankle position), +15 deg (plantarflexed direction), +30 deg and +45 deg. A system of mechanical stops, support triangles and velcro straps was used to secure the subject in the above positions. Location of a moving centre of rotation was calculated for ankle rotations from -30 to 0 deg, -15 to +15 deg, 0 to +30 deg and +15 to +45 deg. All instant centres of rotation were calculated both at rest and during MVC. Achilles tendon moment arms were measured at ankle angles of -15, 0, +15 and +30 deg.
    3. At any given ankle angle, Achilles tendon moment arm length during MVC increased by 1-1.5 cm (22-27 %, P < 0.01) compared with rest. This was attributed to a displacement of both Achilles tendon by 0.6-1.1 cm (P < 0.01) and all instant centres of rotation by about 0.3 cm (P < 0.05) away from their corresponding resting positions.
    4. The findings of this study have important implications for estimating loads in the musculoskeletal system. Substantially unrealistic Achilles tendon forces and moments generated around the ankle joint during a plantarflexor MVC would be calculated using resting Achilles tendon moment arm measurements.

    Changes in Achilles tendon moment arm from rest to maximum isometric plantarflexion: In vivo observations in man (PDF Download Available). Available from: [accessed May 1, 2017].