In vivo mechanical properties of muscular bulk tissue: Mechanical model representation of stress-relaxation behavior

In Vivo mechanical properties of bulk tissue have not been yet investigated sufficiently. One of the major problems the researchers confront is the lack of agreement for the constitutive models and standardized methodology for experimental studies (1). Despite the fact that the tissue properties are non-linear, many modeling studies preferred to adopt linear isotropic models. The object of this study was to obtain bulk modulus of the upper arm under relax and controlled contraction that was 25 % of the maximum voluntary contraction (MVC). A new testing machine was designed and constructed to generate a rapid deformation on the upper arm in order to test stress-relaxation response of the upper arm. A schematic representation of stress-relaxation test design was shown in figure 1. The sudden deformation of the arm was achieved by using computer controlled pneumatic cylinders whose movement was stopped with the adjustable bolt. The desired strain to apply to the upper arm was set by using ruler, the strain was adjusted by the distance between the load cell carrier and the bolt. The load cell was fixed underneath to the load cell carrier. The sudden movement of cylinders were transmitted to the upper arm with squeezing chamber. This device is a cuff that applies controllable strain on a 47 mm wide band of the upper arm. Stress-relaxation response of the upper arm was collected by using load cell. The analog signal from the load cell was digitized by using a 12-bit analog-to digital converter (ADC). The output of the load cell was amplified by a strain gauge amplifier, up to a suitable level for the ADC.