V. Van Toi and T.Q. Dang Khoa (Eds.): ICDBME in Vietnam, IFMBE Proceedings 27, pp. 48–50, 2010. www.springerlink.com Mechanical Behavior of Muscles during Flexion and Extension of Lower Limb on Variable Age Group by Using BRG.LifeMod Nitin Sahai, Ravi P.Tewari, and Lokesh Singh Applied Mechanics Department, Motilal Nehru National Institute of Technology, Deemed University, Allahabad, India Abstract— The main objective of this paper is to find out the muscle which plays a major role during flexion and extension on models of different age groups and the extent of mechanical deformation which takes place in the muscles of lower limb with the help of BRG.Life Mod software which works in ADAM’s environment. The muscles moment is obtained with the help of inverse and forward dynamics simulation of human model that shows us which muscle is active during flexion and extension and how much moment (torque) that muscle is exerting, which causes muscle deformation. According to Hill’s mechanical model of muscle, it consists of three elements: one contractile element attached in series with an elastic element and both of these attached in parallel to an elastic element. During muscles contraction and expansion the deformation of muscles takes place and during one complete gait cycle it regains its original shape and size due to its viscoelastic nature. The deformation in the muscles is obtained by finding the change in the length of muscles during extended flexion and extension in complete gait cycle on different age group models. After conducting the simulation on models of different age group, it is observed that deformation in the muscles of lower limb is maximum obtained in Rectus femoris which is one of the four quadriceps muscles of the human body, the others being Vastus medialis, Vastus intermedius, and Vastus lateralis. On the basis of our experiment the conclusion is made that Rectus femoris plays a major role in regulating knee flexion and extension. Keywords— Flexion & Extension, Hill Muscle Model, Gait cycle. I. INTRODUCTION Muscles provide two kinds of forces, active and passive, which compose a muscles total force. Though actin and myosin “ratching” mechanism muscles will provide the active force while with the help of non contractile element the muscle will provide passive forces, muscles are called as parallel elastic element that contributes to its passive forces. In 1922 A.V. Hill(Hill 1970) first noted that activated muscles produce more force when held isometrically ( at a length fixed) then when they shorten. Muscles co-ordinate muscle joints motion by generating forces that causes reaction forces throughout the body [1]. The motion of walking in human being is divided in to two phases swing phase and support phase. The swing phase is the behavior that the foot leaves the ground surface and the leg swing forward. The support phase is the behavior that the foot stays in the contact with the ground surface and the body is supported by leg [2] as shown in Fig. 2,3,4,5. In this paper the activity of the muscle rectus femoris of lower limb is observed during walking motion of human body of different age in inverse dynamics [3]. The change in the length of rectus femoris is find out during the normal Gait cycle of human being and compared with other muscle activity which helps in finding the strain in particular muscle. The amount of rectus femoris activity is related to walking speed [4] as it plays a crucial role in knee flexion and extension during the Gait cycle of human being [5,6,7,8]. For rectus femoris, the relative work contribution done in knee extension was 21% in jumping and 31% in sprinting[9].The paper’s main focus is given to plot the length v/s time graph of muscle during the gait cycle. II. MECHANICAL MUSCLE MODELHILL’S MODE The Hill model is composed of three elements: two of which are arranged in series which, in turn, are in parallel with the third element. The contractile element is freely extendable when at rest, but capable of shortening when activated by an electrical stimuli. The contractile element is connected to an elastic serial element. The serial element accounts for the muscle elasticity during isometric (constant muscle length) force conditions. The muscle elasticity during isometric contraction is due in a large part to the elasticity of the cross-bridges in the muscle [Fung 93]. These two elements are then joined in parallel with another elastic element used to account for the elasticity of the muscle at rest. The parallel element accounts for the inter-muscular connective tissues surrounding the muscle fibers [5]. Force-Length Properties