Reliability of a test of musculotendinous stiffness for the triceps-surae

Objectives. To determine the inter-day reliability and concurrent validity of a test of unilateral triceps-surae stiffness. Design. Cross-sectional study. Setting. Human Performance Laboratory, University of Technology, Sydney. Participants. Twenty healthy males with no history of injury to the lower body musculature. Main outcome measures. Stiffness measures of the triceps-surae using varying loads of maximum isometric force, conducted approximately seven days apart to assess inter-day reliability. Drop, countermovement and static jump performance, and isometric force and rate of force development (RFD) were also assessed as measures of force production and athletic performance. Results. Intra-class correlation coefficients showed very good reliability for the test of ankle stiffness (r = 0.87-0.94, P < 0.01). Maximal stiffness was also significantly correlated to isometric RFD (P < 0.05). Drop jump performance at various heights in compliant subjects was improved when compared to relatively stiff subjects (P < 0.05-0.01). Conclusions. The current test of unilateral ankle stiffness is both a valid and reliable measure. Stiffness is an important determinant of a joint's force production capabilities and performance in stretch shortening cycle activities. Crown Copyright (C) 2003 Published by Elsevier Ltd. All rights reserved.