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. 1999 Nov 15;521 Pt 1(Pt 1):307-13.
doi: 10.1111/j.1469-7793.1999.00307.x.

In vivo human tendon mechanical properties

C N Maganaris  1 , J P Paul
Affiliations

In vivo human tendon mechanical properties

C N Maganaris et al. J Physiol. .

Abstract

1. The aim of the present study was to measure the mechanical properties of human tibialis anterior (TA) tendon in vivo. 2. Measurements were taken in five males at the neutral ankle position and involved: (a) isometric dynamometry upon increasing the voltage of percutaneous electrical stimulation of the TA muscle, (b) real-time ultrasonography for measurements of the TA tendon origin displacement during contraction and tendon cross-sectional area, and (c) magnetic resonance imaging for estimation of the TA tendon length and moment arm. 3. From the measured joint moments and estimated moment arms, the values of tendon force were calculated and divided by cross-sectional area to obtain stress values. The displacements of the TA tendon origin from rest to all contraction intensities were normalized to tendon length to obtain strain values. From the data obtained, the tendon force-displacement and stress-strain relationships were determined and the tendon stiffness and Young's modulus were calculated. 4. Tendon force and stress increased curvilinearly as a function of displacement and strain, respectively. The tendon force and displacement at maximum isometric load were 530 N and 4.1 mm, and the corresponding stress and strain values were 25 MPa and 2.5 %, respectively. The tendon stiffness and Young's modulus at maximum isometric load were 161 N mm-1 and 1.2 GPa, respectively. These results are in agreement with previous reports on in vitro testing of isolated tendons and suggest that under physiological loading the TA tendon operates within the elastic 'toe' region.

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Figures

Figure 1
Figure 1. Position of the subject on the dynamometer
The knee is flexed at 90 deg with the foot securely fixed at the neutral ankle position. a, velcro straps; b, dynamometer footplate; c, pivot point of the dynamometer; d, knee mechanical stop; e, contra-lateral limb.
Figure 2
Figure 2. Measurement of tendon displacement
Typical sonographs over the TA musculotendinous junction at rest (top), and electrical stimulation of the TA muscle at 75 V (middle) and 150 V (bottom). The white arrow in each scan points to the TA tendon origin. Notice the displacement of the TA tendon origin in the transition from rest to 75 V contraction and from 75 to 150 V contractions.
Figure 3
Figure 3. Changes in joint moment, tendon displacement and force as a function of stimulating voltage
A, dorsiflexion joint moment; B, TA tendon displacement; C, TA tendon force. Data from one subject are presented.
Figure 4
Figure 4. Tendon mechanical properties
A, tendon force-displacement relationship; B, stress-strain relationship; C, stiffness-force relationship; D, Young's modulus-stress relationship. Data from one subject are presented.
See this image and copyright information in PMC

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