Biomechanics & Surgery: Tissue Mechanics V Muscle 2024 PDF

Biomechanics & Surgery: Tissue Mechanics V Muscle Review briefly the structure of muscle and the mechanism of skeletal muscle contraction Examine the factors that influence a muscle’s ability to produce motion Examine the factors that influence a muscle’s ability to produce force Consider how muscle...

Biomechanics & Surgery: Tissue Mechanics V Muscle Review briefly the structure of muscle and the mechanism of skeletal muscle contraction Examine the factors that influence a muscle’s ability to produce motion Examine the factors that influence a muscle’s ability to produce force Consider how muscle architecture is specialized to optimize its ability to produce force or joint motion Demonstrate how an understanding of the above can be used to optimize a person’s performance Discuss adaptations in the muscle with prolong changes in length and/or activity Vassilios G. Vardaxis, Ph.D. Muscle-tendon Terminology Origin Proximal Attachment tendon (proximal) muscle belly - active tendon (distal) insertion Distal Attachment Vassilios G. Vardaxis, Ph.D. The function of Muscles n n n n Muscles always cross at least one joint When a muscle contracts, it produces a force between the two sides of the joint The force generally acts at a distance from the joint center This produces a moment of force about the joint center MUSCLES make MOMENTS Vassilios G. Vardaxis, Ph.D. Muscle Classifications (cont) multi-articular mono-articular bi-articular Vassilios G. Vardaxis, Ph.D. Single-joint and multiple-joint muscles n Single-joint muscles: – produce movement at a single joint n n e.g. adductor magnus Multiple-joint muscles: – may move two or more joints in the same direction, n e.g. long head of biceps brachii – may move one joint while others are static n e.g. gastrocnemius, going on tiptoe – may move joints in opposite directions n e.g. hamstrings Vassilios G. Vardaxis, Ph.D. Mono vs. Bi-articular n n Mono-articular muscles primarily used to generate positive work Bi-articular muscles are used for energy transfer between joints Vassilios G. Vardaxis, Ph.D. Hamstrings Quadriceps produce hip extension via hamstrings Vassilios G. Vardaxis, Ph.D. Lieber (1992) Skeletal muscle structure and function. Lippincott Williams & Wilkins. Gastrocnemius Quadriceps produce plantarflexion via gastrocnemius Vassilios G. Vardaxis, Ph.D. Lieber (1992) Skeletal muscle structure and function. Lippincott Williams & Wilkins. Muscle Architecture Vassilios G. Vardaxis, Ph.D. Muscle Architecture pennation angle force generation axis Vassilios G. Vardaxis, Ph.D. Parallel Vs. q = 0° Pennate q = 30° fiber packing 5 fibers 7 fibers Vassilios G. Vardaxis, Ph.D. FL/ML Ratio FL = Fiber Length ML= Muscle Length n n low number indicates force (0.2) high number indicates velocity (0.6) Vassilios G. Vardaxis, Ph.D. Upper Extremity Muscles Vassilios G. Vardaxis, Ph.D. Lower Extremity Muscles Vassilios G. Vardaxis, Ph.D. Muscle Mechanics n n Def: The study of the external mechanical variables given the internal contractile state of muscle. Thus, study of the length effects, velocity effects, power generation, and force generation in a muscle. Vassilios G. Vardaxis, Ph.D. Contraction Mechanics n n The action responsible for the contraction of a muscle occurs within a sarcomere. The greater the number of cross bridges attached to the actin filaments, the larger the contraction force. Vassilios G. Vardaxis, Ph.D. Contractile Proteins Vassilios G. Vardaxis, Ph.D. Sliding Myofilaments n n Actin and myosin: Force generated by cross bridges Vassilios G. Vardaxis, Ph.D. Contraction Mechanics, cont n n n A single stimulus from the motor neuron results in a twitch response of the fiber. With increased frequency of stimulus (and less time between stimuli), there will still be tension in the fiber when the next stimulus arrives. If the frequency of stimuli is rapid enough, a tetanic response of the fibers results Tension Tension Time Time Vassilios G. Vardaxis, Ph.D. Terms applied to muscular contraction n Concentric – shortening contraction – least force developed when maximally stimulated n Isometric – joint angle remains constant – intermediate force when maximally stimulated n Eccentric – lengthening contraction – greatest force developed when maximally stimulated n Isotonic – uniform tension in muscle – not found in the "real world" n Isokinetic – constant angular velocity – produced during use of "isokinetic dynamometer" (KinCom, Cybex, etc.) Vassilios G. Vardaxis, Ph.D. Agonist, antagonist and synergist n Agonist – the main muscle or "prime mover" n Antagonist – any muscle with an opposing action n Co-contraction – simultaneous contraction of agonist and antagonist n Synergist – a muscle which helps the agonist in some way n Ways in which a synergist may act: – similar action to the agonist – stabilizes neighboring joint – prevents unwanted actions by agonist Vassilios G. Vardaxis, Ph.D. Agonist/Antagonist Foot and Ankle Muscle Activation During Gait Vassilios G. Vardaxis, Ph.D. Tonic and phasic muscles n Tonic or stability muscles – high proportion of slow-twitch (Type I) fibers – used primarily to maintain posture – e.g. soleus n Phasic or mobility muscles – high proportion of fast-twitch (Types IIa & IIb) fibers – used primarily for short powerful actions e.g. biceps Vassilios G. Vardaxis, Ph.D. Vassilios G. Vardaxis, Ph.D. Passive Active Vassilios G. Vardaxis, Ph.D. Active Insufficiency Working Range Passive Insufficiency Vassilios G. Vardaxis, Ph.D. Vassilios G. Vardaxis, Ph.D. Vassilios G. Vardaxis, Ph.D. Length-Tension-Velocity Relationship Length - Tension Velocity - Tension Vassilios G. Vardaxis, Ph.D. Factors affecting maximal joint torque n Muscle cross-sectional area – (0.3-0.4N/sq.mm.) n Position of joint – muscle length (length/tension relationship) – bone orientation (lever arm) n Direction of contraction – eccentric > isometric > concentric n Speed of contraction – slow > fast (for concentric contraction) – fast > slow (for eccentric contraction) Vassilios G. Vardaxis, Ph.D. Muscles in the "real world" n Textbook description – – – – – – muscle contracts concentrically distal segment moves towards proximal segment muscle contracts in isolation gravity is ignored muscle has a single action, e.g. adducts hip muscle is described as agonist n "Real world" situation – – – – – – contraction may be concentric, isometric or eccentric if distal segment is fixed, proximal segment moves co-contraction of antagonists and synergists gravity may oppose, help or produce movement muscle action varies with joint position muscle may be agonist, antagonist or synergist Vassilios G. Vardaxis, Ph.D.