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Changes in Achilles tendon moment arm from rest to maximum isometric plantarflexion: in vivo observations in man
Author(s) -
Maganaris Constantinos N.,
Baltzopoulos Vasilios,
Sargeant Anthony J.
Publication year - 1998
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1998.977bj.x
Subject(s) - achilles tendon , ankle , isometric exercise , sagittal plane , supine position , angular displacement , plantar flexion , anatomy , physics , tendon , rotation (mathematics) , moment (physics) , rest (music) , orthodontics , medicine , mathematics , surgery , geometry , physical therapy , classical mechanics , acoustics
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.