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Jpn J Biomechanics Sports Exercise 13 (3): 108-113, 2009

Effect of the length and stiffness variation in the series elastic element during countermovement: a quantitative study

Hiroshi ARAKAWA1), Akinori NAGANO2), Shinsuke YOSHIOKA1), Senshi FUKASHIRO1)

1)Graduate School of Arts and Sciences, The University of Tokyo

2)Graduate School of Engineering, Kobe University

Abstract

The purpose of this study was to quantify the effect of the length and stiffness variation in the series elastic element (SEE) to the work output during countermovement and the subsequent effects of enhanced work output. A Hill-type model of the muscle tendon complex was constructed. A range of SEE lengths (between 1 and 8 times the optimal length of the contractile element (CE)) and a range of strain rates in the SEE (between 2% and 8%) were investigated. Forward dynamics simulations were performed to evaluate the causal factors for the gain in height during concentric (CO) and countermovement (CM) conditions. Regarding the shorter SEE condition, the magnitude of work output enhancement associated with countermovement was negligible for all of strain rates. In contrast to the longer SEE condition (SEE length was 8 times of that of CE) the magnitude of enhancement was consistent for the moderate strain rates (4% and 8%). These results quantitatively demonstrate the effect of length and stiffness variation in the SEE on the work output during countermovement. The findings would be useful when considering the effect of the compliance in the SEE to the work output during countermovement.

Key Words: elastic energy, stretch-shortening cycle, tendon

Submitted for Publication: Nov. 5, 2008,

Accepted for Publication: June 16, 2009

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