The effect of overshooting the target strain on estimating viscoelastic properties from stress relaxation experiments.
BACKGROUND
Tendon's mechanical behaviors have frequently been quantified using the quasi-linear viscoelastic (QLV) model. The QLV parameters are typically estimated by fitting the model to a single-step stress relaxation experiment. Unfortunately, overshoot of the target strain occurs to some degree in most experiments. This has never been formally investigated even though failing to measure, minimize, or compensate for overshoot may cause large errors in the estimation of parameters. Therefore, the objective of this study was to investigate the effect of overshoot on the estimation of QLV parameters.


METHODS
A simulated experiment was first performed to quantify the effect of different amounts of overshoot on the estimated QLV parameters. Experimental data from tendon was then used to determine if the errors associated with overshoot could be reduced when a direct fit is used (i.e., the actual strain history was used in the curve fit).


RESULTS
We found that both the elastic and viscous QLV parameters were incorrectly estimated if overshoot was not properly accounted for in the fit. Furthermore, the errors associated with overshoot were partially reduced when overshoot was accounted for using a direct fit.


CONCLUSIONS
A slow ramp rate is recommended to limit the amount of overshoot and a direct fit is recommended to limit the errors associated with overshoot, although other approaches such as adjusting the control system to limit overshoot could also be utilized.
Gimbel
Jonathan A
JA
McKay Orthopaedic Research Laboratory, University of Pennsylvania, Philadelphia, PA 19104-6081, USA.
Sarver
Joseph J
JJ
Soslowsky
Louis J
LJ
D000818:Animals; D016477:Artifacts; D003198:Computer Simulation; D004548:Elasticity; D006801:Humans; D008954:Models, Biological; D010812:Physical Stimulation / Q000379:methods*; D013314:Stress, Mechanical; D013710:Tendons / Q000502:physiology*; D014783:Viscosity