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ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

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tendon has a larger moment arm<br />

about the ankle and hence might be<br />

expected to undergo greater motion<br />

with dorsiflexion. The opposite<br />

observation suggests the tendon is<br />

undergoing non-uniform<br />

deformation, with greater alongfiber<br />

stretch arising superficially<br />

and shear deformation developing<br />

across the tendon. This behavior<br />

was consistent across all five<br />

subjects tested.<br />

Changing from an extended to a<br />

flexed knee posture resulted in less<br />

overall tissue motion and a slight<br />

increase in nonuniformity over the<br />

cross-section. Biomechanically, the<br />

flexed knee posture should shorten<br />

the gastrocnemius muscle-tendon<br />

unit substantially beyond its<br />

optimal length for force generation<br />

(Cresswell, et al. 1995). This, in<br />

turn, should increase the relative<br />

loading on the soleus, and hence increase stretch in the portion of the Achilles tendon<br />

that transmits soleus force. Our results were consistent with this idea, as less deep<br />

tendon motion with dorsiflexion could result from greater stretch of the tendon distal to<br />

the ROI. We note that while motion non-uniformity was enhanced in a flexed knee<br />

posture, the deep-superficial differential was relatively small with only a 0.2 mm<br />

difference from the extended knee. Such a result could reflect lateral force transmission<br />

within the tendon that offsets non-uniform loading of the tendon via the gastrocnemius<br />

and soleus.<br />

Non-uniform tendon deformation may be relevant to consider in the context of treating<br />

tendinopathies. Clinically, rehabilitative eccentric exercises have been shown to help<br />

resolve chronic tendinopathies (Alfredson, et al. 1998). It is suggested that this clinical<br />

response may result from stimulating tenocyte activity by inducing shear stresses during<br />

eccentric tendon loading (Fong, et al. 2005, Lavagnino, et al. 2008, Maeda, et al. 2011).<br />

Indeed our studies suggest that shear tissue deformation may arise with lengthening<br />

Achilles tendon loading. Future studies will consider how tissue motion non-uniformity<br />

varies between concentric and eccentric loading conditions, which could provide further<br />

insight into the mechanisms by which eccentric rehabilitation may promote tendon<br />

healing.<br />

6. REFERENCES<br />

Fig. 3. Gross measures of ankle dorsiflexion and<br />

moment were obtained from the inertial loading<br />

device. Achilles tendon loading, as indicated by<br />

the ankle moment, peaked with ankle<br />

dorsiflexion. Distal motion of the tendon<br />

corresponded with ankle dorsiflexion.<br />

1. Maffulli, N., Walley, G., Sayana, M. K., Longo, U. G. and Denaro, V., Eccentric calf<br />

muscle training in athletic patients with achilles tendinopathy, Disabil. Rehabil.,

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