Classification of muscles Cardiac Muscles Involuntary Smooth Muscles Non striated- involuntary Small intestines muscles Skeletal Muscles Striated- Mainly voluntary Upper and lower limb muscles

Skeletal muscles They are a force generator system which provide strength and protection to the skeleton by distributing loads and absorbing shocks. Human body has approx. 430 muscles existing in pairs (right and left). They account for 40-45% of total body weight in adults. They attached to skeleton via tendons and by muscle contraction joints can move which allow body movement. They permit bodily movements in space and maintain body posture.

Epimysium: surround whole muscle. Perimysium: located between muscle bundles. Endomysium: surround each muscle fiber.

Sarcomere (functional unit of the muscle) Dark A band: full of actin and myosin filaments. H zone : in the center of dark band (no actin filaments). Light I band : full of actin filaments only. Z line : the center of light band. Sarcomere: area between two z lines, it contract and relax as one unit.

Factors affecting mechanics of muscles I-Muscle architecture Muscle model Sarcomere arrangement II-Muscle properties 1-Contractility 2-Distensibility 3-Elasticity 4- Viscosity 5-Time dependent mechanical properties III-Muscle Variables IV Muscle training

I-Muscle architecture 1) Muscle model. It includes 3 components:  Contractile component (CC).  Series elastic component (SEC).  Parallel elastic component (PEC). It is mechanical model that describes the function of the muscle tissue during activity and during rest.

I-Muscle architecture 1- Muscle model Contractile component (CC) Overlap of the actin and myosin Active tension Series elastic component (SEC) connective tissues within the tendon 1- Smoothen out the rapid changes in the muscle tension. 2- Passive tension. Parallel elastic component (PEC) Parallel connective tissues: sarcolemma, epimysium, perimysium, endomysium passive tension.

I-Muscle architecture 2- Sarcomere arrangement Parallel arrangement Designed for force production e.g. Quadriceps muscles Series arrangement Designed for rapid contraction e.g. Sartorius muscle

II-Muscle Properties 1-Contractility 2-Distensibility 3-Elasticity 4- Viscosity 5-Time dependent mechanical properties

It is the ability of the muscle to shorten and produce tension between its ends. 1-Contractility 2-Distensibility It is the ability of the muscle tissue to be stretched or lengthened in response to an externally applied load.

It means the muscle's internal resistance to elongation increases with the rate of stretch. Viscosity helps protect a muscle from being damaged by a quick and forceful stretch. 3-Elasticity It is the resistance to distortion and is the opposite of distensibility. It refers to the property of the tissue to return to its unstrained (original) length after being deformed. 4- Viscosity

The progressive strain or deformation of the material when exposed to a constant load over time. 5-Time dependent mechanical properties a- Creeping

The decrease in stress in a deformed structure over time when the deformation is held constant 5-Time dependent mechanical properties b- Stress relaxation

III-Muscle Variable 1-Muscle length 2- Force (tension) 3-Torque (moment) 4- Velocity 5- Power

The length that allows the greatest number of cross- bridge attachments and therefore the greatest active force. 1-Muscle length Stretched Muscle Shorted Muscle Optimal resting length Equilibrium length The length of isolated uncontracted muscle. If the muscle is removed from its attachments, it will shorten to about 10% of its original length.

Muscle force varies according to its length. Length tension relationship: e.g. during isometric contraction Active tension: by contractile element  inverted U shape. Passive tension: by parallel & series elastic components. Active + Passive tensions => total tension 2- Force (tension)

Pre-contraction stretch will result in greater amount of tension generated by the non-contractile element of muscle. Muscle performs more work when it shortens immediately after being stretched in the concentrically contracted state than when it shortens from a state of isometric contraction. This due to elastic energy stored in the elastic components during stretching then released during muscle contraction in addition to energy stored in the contractile component.

Factors affecting muscle force Force-time relationship Effect of fatigue Type of muscle fiber

the longer the time required for the muscle to contract, the greater is the force developed, up to point of maximum tension. Eccentric contraction leads to greater force production because time is allowed for the tension produced by contractile elements to be transmitted to the non-contractile elements (tendon). Force-time relationship

The ability of muscle to contract and relax is dependent on the availability of ATP needs. If the muscle has an adequate supply of oxygen and nutrients which can be broken down to provide needed ATP & subject can continue exercise for long period. If the frequency of ex’s exceed the rate of ATP synthesis Muscle fatigue will occur. Effect of Fatigue

When a muscle begin to fatigue, rest period should be given to allow this muscle to resume its normal performance level. Rest period varies according type and intensity of exercise. e.g. muscle that rapidly fatigue by high intensity and short duration exercise recover after a rest period of seconds to few minutes. In contrast, a muscle that is slowly fatigued by low intensity, long duration exercise requires up to 24 hours for recovery. Effect of Fatigue

3 types of muscle fiber are found in human being: type I (slow-twitch or slow oxidative), type IIA (fast oxidative glycolytic), type IIB (fast glycolytic). 15%IIB Approximately 50-55% of muscle fibers are type I, 30-35% are type IIA and 15% are type IIB. These percentages differ greatly among individual. Endurance athlete may have 80% type I fibers, in contrast those engaged short explosive efforts may have 30% of these fibers Types of muscle fiber

Comparison between different Types of muscle fiber Type I (SO)Type IIA (FOG)Type IIB (FG) Speed of contraction SlowFast Rate of fatigueSlow (fatigue resistant) Fast (fatigue resistant) Fast (fatigable) Myoglobin contentHigh Low Muscle tensionLow tensionHigh tension MitochondriaMany Low Suitable forProlonged low intensity work Relatively long period activity Short duration activity ExampleDistance runnerFootball playersSprinters