In vivo stiffness measurement and in silico stiffness prediction of biceps brachii muscle using an isometric contraction exercise

Cadavers are often used to measure the material properties of muscle via the static tensile loading test. However, the mechanical properties of the cadaver are different from that of in vivo muscle. In this work, a new way to measure the stiffness of in vivo muscle was proposed based on a vibration test combined with measured electromyography (EMG) signals. The stiffness of the biceps brachii muscle during isometric contractions with various weights (0 - 11 kg) was measured from the vibration test utilizing support properties of a spring attached to a mass. The relationship between the load level, the EMG signal, and the muscle stiffness was investigated and a multiple- spring model for biceps brachii muscle was newly suggested. Also, simulation using a commercial bio-mechanics simulation software (LifeMOD) was conducted to verify the developed muscle spring model and the measured stiffness of the in vivo muscle. The in vivo stiffness of the biceps brachii measured experimentally agreed well with the simulation result.