The role of muscle strength on tendon adaptability in old age

D Holzer,A Mierau,G M Kukuk,G Epro,J A Luetkens,L Scheef,G.-P Brüggemann,H Boecker,K Karamanidis,J Doerner,C N Maganaris,C Mccrum

doi:10.1007/s00421-018-3947-3

Abstract

PurposeThe purpose of the study was to determine: (1) the relationship between ankle plantarflexor muscle strength and Achilles tendon (AT) biomechanical properties in older female adults, and (2) whether muscle strength asymmetries between the individually dominant and non-dominant legs in the above subject group were accompanied by inter-limb AT size differences.MethodsThe maximal generated AT force, AT stiffness, AT Young’s modulus, and AT cross-sectional area (CSA) along its length were determined for both legs in 30 women (65 ± 7 years) using dynamometry, ultrasonography, and magnetic resonance imaging.ResultsNo between-leg differences in triceps surae muscle strength were identified between dominant (2798 ± 566 N) and non-dominant limb (2667 ± 512 N). The AT CSA increased gradually in the proximo-distal direction, with no differences between the legs. There was a significant correlation (P < 0.05) of maximal AT force with AT stiffness (r = 0.500) and Young’s modulus (r = 0.414), but only a tendency with the mean AT CSA. However, region-specific analysis revealed a significant relationship between maximal AT force and the proximal part of the AT, indicating that this region is more likely to display morphological adaptations following an increase in muscle strength in older adults.ConclusionsThese findings demonstrate that maximal force-generation capabilities play a more important role in the variation of AT stiffness and material properties than in tendon CSA, suggesting that exercise-induced increases in muscle strength in older adults may lead to changes in tendon stiffness foremost due to alterations in material rather than in its size.

Highlights

Tendons transmit muscle forces to the skeleton to allow body movement and interaction with the environment
The post hoc test showed that cross-sectional area (CSA) at Int 100% was significantly (P < 0.05) smaller than mean CSA at Int 10–70%; Int 90% < Int 10–60%; Int 80% < Int 10–60%; Int 70% < Int 10–50%; Int 60% and Int 50% < Int 10–40%; Int 40% < Int 10–20%; and Int 30% and Int 20% < Int 10%
No significant correlations were found between the symmetry indexes of maximal Achilles tendon (AT) force and mean AT CSA, or between the symmetry indexes of maximal AT force and AT CSA at the length intervals studied

Summary

Introduction

Tendons transmit muscle forces to the skeleton to allow body movement and interaction with the environment. Other cross-sectional and interventional studies (Bayliss et al 2016; Kubo et al 2001; Reeves et al 2003; Malliaras et al 2013) show that differences in tendon stiffness seem to be entirely or largely due to altered material properties It seems that at least in younger individuals, tendon material and morphological adaptations occur over different time frames, with changes in material properties taking place earlier within an exercise training programme, whereas tendon hypertrophy appears to be a longer term adaptive response (Kjaer et al 2009; Heinemeier and Kjaer 2011; Bohm et al 2015a; Wiesinger et al 2015). What leads to these diverse tendon adaptations to increased mechanical loading is not yet fully understood

Objectives

Methods

Results

Discussion

Conclusion