Abstract
BackgroundMechanical loading is crucial for muscle and tendon tissue remodeling. Eccentric heel drop exercise has been proven to be effective in the management of Achilles tendinopathy, yet its induced change in the mechanical property (i.e., stiffness) of the Achilles tendon (AT), medial and lateral gastrocnemius muscles (MG and LG) was unknown. Given that shear wave elastography has emerged as a powerful tool in assessing soft tissue stiffness with promising intra- and inter-operator reliability, the objective of this study was hence to characterize the stiffness of the AT, MG and LG in response to an acute bout of eccentric heel drop exercise.MethodsForty-five healthy young adults (36 males and nine females) performed 10 sets of 15-repetition heel drop exercise on their dominant leg with fully-extended knee, during which the AT and gastrocnemius muscles, but not soleus, were highly stretched. Before and immediately after the heel drop exercise, elastic moduli of the AT, MG and LG were measured by shear wave elastography.ResultsAfter the heel drop exercise, the stiffness of AT increased significantly by 41.8 + 33.5% (P < 0.001), whereas the increases in the MG and LG stiffness were found to be more drastic by 75 + 47.7% (P < 0.001) and 71.7 + 51.8% (P < 0.001), respectively. Regarding the AT, MG and LG stiffness measurements, the inter-operator reliability was 0.940, 0.987 and 0.986, and the intra-operator reliability was 0.916 to 0.978, 0.801 to 0.961 and 0.889 to 0.985, respectively.DiscussionThe gastrocnemius muscles were shown to bear larger mechanical loads than the AT during an acute bout of eccentric heel drop exercise. The findings from this pilot study shed some light on how and to what extent the AT and gastrocnemius muscles mechanically responds to an isolated set of heel drop exercise. Taken together, appropriate eccentric load might potentially benefit mechanical adaptations of the AT and gastrocnemius muscles in the rehabilitation of patients with Achilles tendinopathy.
Highlights
The calf muscle situated at the posterior side of the lower legs is composed of gastrocnemius (medial (MG) and lateral (LG)) and soleus, in connection with Achilles tendon (AT) to form a musculotendinous unit
Acute and subacute tendon adaptation responses immediately following weight-bearing exercises could largely contribute to tendinopathy (Tardioli, Malliaras & Maffulli, 2012), it is imperative to determine appropriate mechanical loading of each type of exercise training program as reflected by immediate changes in tendon stiffness
Eccentric calf muscle exercise was demonstrated to induce acute changes on the transverse morphology and strain of the AT in healthy, recreationally active adults (Grigg, Wearing & Smeathers, 2009; Obst, Newsham-West & Barrett, 2015), and thickness alteration of the AT assessed by ultrasonography was conferred as a promising prognostic parameter for predicting Achilles tendinopathy within six to 12 months in asymptomatic and symptomatic patients (Bakkegaard et al, 2015; Fredberg & Bolvig, 2002)
Summary
The calf muscle situated at the posterior side of the lower legs is composed of gastrocnemius (medial (MG) and lateral (LG)) and soleus, in connection with Achilles tendon (AT) to form a musculotendinous unit. Acute and subacute tendon adaptation responses immediately following weight-bearing exercises could largely contribute to tendinopathy (Tardioli, Malliaras & Maffulli, 2012), it is imperative to determine appropriate mechanical loading of each type of exercise training program as reflected by immediate changes in tendon stiffness. Eccentric heel drop exercise has been proven to be effective in the management of Achilles tendinopathy, yet its induced change in the mechanical property (i.e., stiffness) of the Achilles tendon (AT), medial and lateral gastrocnemius muscles (MG and LG) was unknown. The gastrocnemius muscles were shown to bear larger mechanical loads than the AT during an acute bout of eccentric heel drop exercise. Appropriate eccentric load might potentially benefit mechanical adaptations of the AT and gastrocnemius muscles in the rehabilitation of patients with Achilles tendinopathy
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