2Objectives1. Describe the structure and properties of the whole muscle, fast and slow twitch muscle fibers, and the myofibril. 2. Explain how the relationship of the muscle line of pull to the joint axis affects the movement produced by the muscle. 3. Describe the relationship between skeletal muscle fiber arrangement and function. 4. Define the roles a muscle may play and explain the cooperative action of muscles in controlling joint actions by naming and explaining the muscle roles in a specified movement. 5. Define the types of muscular contraction, name, and demonstrate each type of action. 6. Demonstrate an understanding of the influence of gravity and other external forces on muscular action. 7. Describe various methods of studying muscle action. 8. State force-velocity and length-tension relationship and explain the significance to static & dynamic movements. 9. Identify muscle groups active in a variety of motor skills.
3SKELTAL MUSCLE STRUCTURE: Properties of Muscular Tissue Extensibility and Elasticity: enable the muscle to be stretched and return to normal length.Tendons are continuations of muscle’s connective tissue and also possess these properties.Contractility: is the ability to shorten and produce tension.
4The Muscle FiberConsists of myofibrils held together by sarcolemma (cell membrane) that can propagate nerve impulses.Fig 3.1
5The Muscle Fiber: Myofibrils Are arranged in parallel formation.Made up of alternating dark & light bands that give muscle fiber their striated appearance.Each fiber enclosed by endomysium.
6The Muscle Fiber: Myofilaments Fig 3.2Actin: when stimulated slides over myosin.Cross-bridges: projections (heads) of myosin attach to actin.
7The Muscle Fiber: Sarcomeres Fig 3.2Myofibril between two Z lines.Functional contractile unit of skeletal muscle.
8The Muscle Fiber: Whole Muscle Fig 3.1Fasiculus (bundle of fibers) enclosed by perimysium.Group of bundles encased within epimysium.
9Slow and Fast Twitch Fibers These are the two major categories pertinent for kinesiology.Most limb muscles contain a relatively equal distribution of each fiber type.Postural muscles contain more slow twitch fibers.Fast twitch fibers are large, pale, and have less blood supply than slow twitch fibers.Two primary types are IIa (fast oxidative glycolitic) and IIb (fast glycolitic).Suitable for intense responses over a short period of timeSlow twitch fibers are small, red, and have a rich blood supply, and greater myoglobin.Highly efficient, do not fatigue easily.Suitable for long duration, posture and endurance events.
10Muscular AttachmentsMuscles attach to bone by connective tissue, which continues beyond the muscle belly to form a tendon.Origin: usually more proximalInsertion: usually more distalContraction produces equal force on the two attachments.Origin usually stabilized by other muscles.Reverse Muscle Action: occurs when the distal bone is stabilized and the proximal bone moves.
11Structural Classification of Muscles by Fiber Arrangement Fig 7.15Longitudinal: long, strap like muscle with fibers in parallel to its long axis.Sartorius
12Structural Classification of Muscles by Fiber Arrangement Quadrate or Quadrilateral: four sided and usually flat.Consist of parallel fibers.RhomboidsFig 3.10b
13Structural Classification of Muscles by Fiber Arrangement Triangular: fibers radiate from a narrow attachment at one end to a broad attachment at the other.Pectoralis majorFig 5.11
14Structural Classification of Muscles by Fiber Arrangement Fig 6.8Fusiform or Spindle-Shaped: rounded muscle that tapers at either end.Brachioradialis
15Structural Classification of Muscles by Fiber Arrangement Fig 8.25Pennate: a series of short, parallel, feather like fibers extends diagonally from the side of a long tendon.Tibialis posterior
16Structural Classification of Muscles by Fiber Arrangement Bipennate: A long central tendon with fibers extending diagonally in pairs from either side of the tendon.Rectus femorisFig 7.15
17Structural Classification of Muscles by Fiber Arrangement Multipennate: Several tendons are present, with fibers running diagonally between them.Middle deltoidFig 5.11
18Effect of Muscle Structure on Force Force a muscle can exert is proportional to its physiological cross section (PCS).A broad, thick, longitudinal muscle exerts more force than a thin one.A pennate muscle of the same thickness as a longitudinal muscle can exert greater force.The oblique arrangement of fiber allows for a larger number of fibers than in comparable sizes of other classifications.
19Effect of Muscle Structure on ROM Muscle can shorten to approximately half its’ resting length.Long muscles with fibers longitudinally arranged along the long axis can exert force over a longer distance.Pennate muscles with their oblique fiber arrangement and short fibers, can exert superior force through only a short range.
20SKELETAL MUSCLE FUNCTION: Line of Pull Fig 3.4Movement that the contracting muscle produces is determined by two factors:Type of joint that is spansThe relation of the muscle’s line of pull to the jointPectoralis major (clavicular) is primarily a flexor, but it also adducts the humerus.When arm is abducted, line of pull moves above axis of rotation and contributes to abduction of humerus.
21Angle of AttachmentIf very shallow, most of the tension will produce a force pulling along the bone.Will tend to stabilize joint.If fairly large, will have a much larger rotary component of force.In many muscles the angle changes throughout ROM.When muscle generates tension at a 900 angle to the bone, it is the most efficient at producing joint motion.
22Types of Contraction Contract literally means to “draw together”. Muscle contraction occurs whenever muscle fibers generate tension which may occur while the muscle is actually shortening, remaining the same length, or lengthening.
23Concentric or Shortening Contraction Fig 3.5cWhen tension by the muscle is sufficient to overcome a resistance and move the body segment.The muscle shortens.Fig 3.5aWhen a muscle slowly lengthens as it gives in to an external force that is greater than the contractile force it is exerting.Muscle is acting as a “brake”.
24Isometric or Static Contraction Isometric means “equal length”.Tension is developed in the muscle without any appreciable change in length.Occurs under two conditions:1. Antagonistic muscles contract with equal strength.2. Muscle is held against another force.Isotonic means “equal tension” - the tension remains constant while muscle shortens or lengthens.Isokinetic means “equal or same motion”.Maximum muscle effort at the same speed.“Accommodating resistance”.
25Influence of GravityMovements may be in the direction as gravitational forces (downward), opposing gravity (upward), or perpendicular to gravity (horizontal).Horizontal motion is not affected by gravity.Lifting against gravity requires a concentric contraction of the agonist.Slowly lowering with gravity requires an eccentric contraction of the same muscle.A forceful downward motion uses agonist muscles in a concentric contraction, since gravitational pull is being exceeded.Fig 3.6
26Length-Tension Relationship Optimum length is the length at which a muscle can exert maximum tension.Slightly greater than resting length.1. Passively stretched2. Total tension3. Developed tensionFig 3.7123
27Force-Velocity Relationship As the speed of contraction increases, the force it is able to exert decreases.At maximum velocity of contraction the load is zero.Fig 3.8
28Stretch-Shortening Cycle Both muscle and tendon possess elastic properties.When concentric contraction is preceded by a phase of active stretching, elastic energy stored in the stretch phase is available for use in the contractile phase.This enhanced potential for work is attributed to a combination of the series elastic components (tendon) and the parallel elastic components (cross bridge and fascicle elasticity; stretch reflex).
29COORDINATION OF THE MUSCULAR SYSTEM Movements of the body use considerable activity in muscles in addition to those directly responsible for the movement.Muscles causing the movement must have a stable base.Bones not engaged in the movement must be stabilized by other muscles.
30Roles of MusclesMovers, or Agonists: directly responsible for producing a movement.Prime movers: large impact on movementAssistant movers: only help when neededThis distinction between the various muscles that contribute to a movement is not always clearly defined.
31Roles of Muscles Synergists: cooperative muscle function Fig 3.9Synergists: cooperative muscle functionStabilizing, Fixator, & Support MusclesNeutralizers – prevent undesired actionThe rhomboids stabilize the scapula against the pull of the teres major.Fig 3.10
32Roles of MusclesAntagonists: have an effect opposite to that of movers, or agonists.Check ballistic movementsFirst: Antagonists must relax to permit movement.Second: Acts as a brake at completion of movement.
33Cocontraction The simultaneous contraction of movers and antagonists. Neutralizers and stabilizers may need to cocontract to counteract the additional function of a mover.
34Action of Bi-Articular Muscles Muscles that pass over and act on two jointsWhether muscles flex joints in the same direction or opposite directions, they are not long enough to permit complete movement in both joints at the same time.Resulting tension in one muscle is transmitted to the other.Bi-articular muscles can continue to exert tension without shortening.
35Action of Bi-Articular Muscles Concurrent Actions: Simultaneous flexion or extension of the hip and knee joints.No net change in length of either muscle.Fig. 3.11aFig. 3.11bCountercurrent Action: one muscle shortens at both joints as the antagonist lengthens correspondingly and thereby gains tension at both ends.
36Types of Bodily Movements Passive: no effort on the part of the subject involved, motion due to outside force.Active: movement is produced by the subject’s own muscular activity.In slow movements muscular tension is maintained throughout ROM.In rapid movements, tension could be maintained throughout ROM, but this is an inefficient way of performing.
37Ballistic MovementMovements that are initiated by vigorous contraction and completed by momentum.Throwing, striking, & kickingIn the early stages of learning concentrate on form rather that accuracy.Termination of ballistic action:1. By contracting antagonist muscles.Forehand drive in tennis2. By passive resistance of ligaments or other tissues at limits of motion.Throwing motion3. By the interference of an obstacleChopping wood
38METHODS OF STUDYING THE ACTION OF MUSCLES Fig 3.12Conjecture & Reasoning: Using knowledge of location and attachments, and nature of joints, one can deduce a muscle’s action.Muscle attachments & line of pull determine possible movements.Dissection: meaningful basis for the visualization of muscle’s potential movements.Inspection & Palpation: valuable method for superficial muscles.Models: used for demonstration.Muscle Stimulation: contraction of individual muscles.
39METHODS OF STUDYING THE ACTION OF MUSCLES Electromyography (EMG): based on the fact that contracting muscles generate electrical impulses.Reveals both intensity& duration of muscleactivity.Cannot indicatenature of contractionor muscle action.Fig. 3.13
40MUSCULAR ANALYSISDescription of muscular involvement is added to previously completed analysis of joint and segment involvement.Muscular action is identified for each joint movement and recorded next to the joint action on the chart (Table 1.2).Main Muscle Groups ActiveKind of Contraction
41Anatomical Analysis of the Standing Long Jump:(Preparation Phase) JointJoint ActionSegment movedPlane & AxisForceContraction typePrime moversAnkleDorsi-flexionShankSag/bilatGravityEccentricGastrocnemius, soleus, peroneus longusKneeFlexionThighQuadriceps femorisHipTrunkhamstringsShoulderHyper-ExtensionUpper armMuscleConcentricLatissimus dorsi, teres major, post.deltoidElbowLower armTriceps brachii, anconeus
42Anatomical Analysis of the Standing Long Jump: (Power Phase) JointJoint ActionSegment movedPlane & AxisForceContraction typePrime moversAnklePlantar-FlexionShankSag/bilatMuscleConcentricGastrocnemius, soleus, peroneus longusKneeExtensionThighQuadriceps femorisHipTrunkHamstringsShoulderFlexionUpper armPectoralis major, anterior deltoidElbowLower armTriceps brachii, anconeus