Introduction Achilles tendinopathy (AT) is a common condition. Its pathoaetiology is not fully understood although failed loading is believed to be a key feature in its pathogenesis.2 The Achilles tendon is a key structure involved in the stretch shortening cycle and aberrations in stretch-shortening cycle behaviour may be associated with the pathoaetiology of AT.1 The purpose of this study was to describe the stretch shortening cycle behaviour of the ankle and lower limb in patients with AT and compare it with healthy volunteers. In doing so, our understanding of the relationship between stretch shortening cycle behaviour and AT will be enhanced.
Methods Fifteen patients with AT (mean age 41.2 ± 12.7 years) and eleven healthy control volunteers (CON) (mean age 23.2 ± 6.7 years) performed sub-maximal single-limb hopping on a custom built sledge-jump system. Using 3D motion analysis and surface EMG, temporal kinematic (lower limb stiffness, ankle angle at 80 ms pre-contact, ankle angle at contact, peak ankle angle, ankle stretch amplitude) and EMG measures (onset, offset and peak times relative to contact) were captured for soleus (S) and tibialis anterior (TA). Data between AT and CON were compared statistically using a linear mixed model.
Results Patients with AT exhibited significantly increased lower limb stiffness when compared to healthy volunteers (p < 0.001) and their hopping range was shifted towards a more dorsiflexed position (p < 0.001). Furthermore, ankle stretch amplitude was greater in AT compared with healthy volunteers (p < 0.001). A delay in muscle activity was also observed; soleus onset (p < 0.001), tibialis anterior peak (p = 0.026) and tibialis anterior offset (p < 0.001) were all delayed in AT compared with CON.
Discussion These findings indicate that patients with AT exhibit altered stretch-shortening cycle behaviour during sub-maximal hopping when compared with healthy volunteers. Specifically, patients with AT hop with greater lower limb stiffness, in a greater degree of ankle dorsiflexion and have a greater stretch amplitude. Likewise, delayed muscle activity was evident. These findings have implications in terms of informing the understanding of the pathoaetiology and management of AT.
References 1 Maquirrian. Int J Sport Med. 2012;33:567–571
2 Neviaser, et al. J Sh Elb Surg. 2012;21:158–163
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