Elsevier

Journal of Biomechanics

Volume 33, Issue 11, 1 November 2000, Pages 1453-1459
Journal of Biomechanics

In vivo human tendinous tissue stretch upon maximum muscle force generation

https://doi.org/10.1016/S0021-9290(00)00099-3Get rights and content

Abstract

In the present study, we examined the hypothesis that stretch of tendinous tissue in the human tibialis anterior (TA) muscle–tendon unit upon isometric dorsiflexion maximum voluntary contraction (MVC) varies along the entire tendinous component length. Ultrasound-based measurements of the excursions of the TA tendon origin and proximal end of the TA central aponeurosis were taken in the transition from rest to MVC in six men. Subtracting the TA tendon origin excursion from the excursion of the aponeurosis proximal end, the aponeurosis excursion was estimated. Estimation of the aponeurosis proximal region excursion was obtained subtracting the excursion of the insertion point of a central region fascicle on the aponeurosis from the whole aponeurosis excursion. Subtracting tendon excursion from the excursion of the central fascicle insertion point, the aponeurosis distal region excursion was estimated. Strain values were calculated dividing the excursions obtained by the original resting lengths. All excursions and lengths were measured in the mid-longitudinal axis of the TA muscle–tendon unit at the neutral anatomical ankle position. Tendon excursion and strain were 0.5±0.08 cm (mean±SE) and 3.1±0.2%, respectively. Aponeurosis excursion and strain were 1.1±0.15 cm and 6.5±0.6%, respectively. Aponeurosis distal region excursion and strain were 0.3±0.05 cm and 3.5±0.3%, respectively. Aponeurosis proximal region excursion and strain were 0.8±0.12 cm and 9.2±1%, respectively. Aponeurosis excursion and strain were larger by 110–120% (P<0.05) compared with tendon. Aponeurosis proximal region excursion and strain were larger by 165–170% (P<0.05) compared with aponeurosis distal region. These findings are in line with results from in vitro animal material testing and have important implications for theoretical models of muscle function.

Introduction

The effect of tendinous tissue elasticity on static and dynamic muscle performance has long been recognized (for review see Alexander, 1981; Zajac, 1989). Results from in vitro tensile testing of isolated animal or human material are fairly consistent suggesting that at maximal static muscle force, tendinous tissue strains 2–5% (Ker et al., 1988; Lieber et al., 1991; Zajac, 1989). On most of the experiments performed however, (a) preserved or deep-frozen material that may have altered properties (Smith et al., 1996) has been used and (b) predicted maximal muscle forces from estimated values of muscle cross-sectional area and stress have been applied (e.g. Ker et al., 1988; Loren and Lieber, 1995). Even more importantly, measurements have been traditionally performed on the extramuscular portion of tendon excluding the intramuscular tendon, the so-called “aponeurosis” (e.g. Ker et al., 1988; Bennett et al., 1986). Studies in which both tendon and aponeurosis elongations upon maximal load application have been measured simultaneously have shown that tendon and aponeurosis strain similarly (Rack and Westbury, 1984; Trestik and Lieber, 1993) or that aponeurosis strain is larger as compared with tendon (Huijing and Ettema, 1988/1989; Ettema and Huijing, 1989; Lieber et al., 1991). Moreover, a non-uniform aponeurosis strain has been reported indicating that regional differences in compliance may exist along the aponeurosis axial axis (Zuurbier et al., 1994). No in vivo human studies have been ever performed to verify these findings. Differences in strain between tendon and aponeurosis, and regional differences in aponeurosis strain would have to be considered when studying differences in length changes upon contraction between fibre and muscle, but even more importantly when estimating (a) changes in muscle geometry upon contraction, (b) the muscle force–length relationship and (c) the muscle force–velocity relationship. Such information is relevant to models used in biomechanics and clinical research for simulation of the mechanical behaviour of individual muscles in multi-muscle systems, allowing prediction of net joint force and moment (e.g. Zajac, 1989; Brand et al., 1994).

Real-time ultrasonography allows in vivo recording of human tendinous tissue movement upon muscle contraction (Fukunaga et al., 1996). Using this methodology in the present study we aimed at (a) examining whether differences in strain upon maximal isometric dorsiflexion force exist between the human tibialis anterior (TA) muscle central aponeurosis and extramuscular tendon, and (b) testing the hypothesis that the TA aponeurosis strains non-uniformly along its length.

Section snippets

Experimental protocol

Measurements were taken in six healthy males [average (mean±SE) age, height, body mass and lower leg length: 22±2 yr, 172±2 cm, 74±3 kg and 40±1.5 cm, respectively], who volunteered to participate in this study, which had been approved by the local ethics committee. The subjects performed a series of isometric dorsiflexion maximum voluntary contractions (MVCs) in the prone position on an isokinetic dynamometer (Lido Active, Loredan Biomedical, Davis) with the knee of the tested leg (right in all

Results

The TA tendon origin, the aponeurosis proximal end and the central fascicle insertion point shifted proximally in the transition from rest to MVC (Fig. 3). Our scan morphometrics yielded excursions ranging between 0.5±0.08 and 1.6±0.25 cm (Fig. 4). The excursion of the aponeurosis proximal end was larger by 0.8 cm (100%, P<0.05) compared with the central fascicle insertion point, whose excursion was larger by 0.3 cm (60%, P<0.05) compared with the TA tendon origin. The calculated excursions of

Discussion

The present results demonstrate that stretch of tendinous tissue in the TA muscle–tendon unit in the transition from rest to MVC varied along the entire tendinous component length.

The tendon strain in the present study was 3.1%. This value lies within the strain range of 2–5% obtained from tensile testing of in vitro human and animal tendon material upon loading equivalent to maximal isometric muscle force (Ker et al., 1988; Lieber et al., 1991; Trestik and Lieber, 1993; Loren and Lieber, 1995

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