Leg Stiffness Represents More Movement Characteristics than Structural Differences

Y.-Y. Ju, C.-C. Chang, H.-Y.K. Cheng, C.-C. Chen, and M.-J. Wu (Taiwan)


Stiffness, Age, Ground reaction force, Stairs, Landing


Researchers have demonst rated that sti ffness is an important biomechanical parameter during human movements. While current knowledge supports the potential effects of ageing on tissues and movements, however, available investigations did not show consistent results for the role of ageing on influencing stiffness. We assume this mismatch results at least partially from improper test settings. This study was therefore designed to investigate the role of ageing on leg stiffness by comparing leg stiffness of the old and young people measured in two functional ways--walking down stairs and landing from a stair. In total 17 elderly and 17 young individuals (mean age 67.5 and 24.5) were instructed to walk down stairs and to perform a single-leg landing from a stair of 25cm in height. Ground reaction forces were measured for calculating three stiffness parameters— stairing down, stepping onto floor, and landing from a stair. Results showed that the old group demonstrated significantly lower SS (16.5±7.5 kN/m) than the young group did (22.1±7.3 kN/m). Similar results were found for FS (23.3±6.7 versus 28.1±8.4 kN/m) but not LS (25.5±7.0 versus 24.1±5.5 kN/m). These indicated that old individuals employed a unique manner during stepping downstairs. Furthermore, during a single-leg landing in which little play of strategic movement control was allowed, stiffness is not sensitive to structural differences. We concluded that the stiffness calculated from the ground reaction force represents more the movement characteristics than structural differences of the individuals.

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