D. Glenn Hunter, Vince Coveney and Jonathon Spriggs
Objective: The purpose of the study was to investigate the effect of static stretching on the active
stiffness and damping characteristics of the ankle joint plantar flexors. Design: The study was an
experimental design. Background: Flexibility has static and active components. Little information is
available regarding the effect of static stretching on the active stiffness of the muscle tendon unit.
This may have relevance in relation to muscle tendon unit injury and the assessment of flexibility.
Methods: Pre- and post-intervention free oscillation data representing active stiffness was obtained
in 30 subjects using applied masses equivalent to 30% of the subject's maximal voluntary contraction (MVC). The control group (n = 15) rested between measurements, the experimental group performed 10 x 30 second static stretches for the ankle joint plantar-flexors. Results: No statistically significant differences were found for stiffness values (P = 0.71 95%; CI - 1503±2172) and damping values
(P = 0.94 95%; CI - 0.0272±0.0195) between the control and stretching group.
The trend was an increase in both parameters following stretching. Conclusions: The results imply
that static stretching had no statistically significant effect on the active stiffness or damping characteristics of the muscle tendon unit as measured with applied masses equating to 30%
maximal voluntary contraction. The low statistical power of the study should be considered in
evaluating the results. Relevance: Flexibility is a construct with different components of
measurement. Studies typically relate static flexibility measurements or exercises to injury with
conflicting outcomes. This study suggests that static stretching may have no effect on active stiffness
of the ankle plantar-flexors and that these findings may have value in the design of stretching
programs and in aetiological studies pertaining to flexibility.
2001 Harcourt Publishers Ltd