Sport Books Publisher1 Chapter 3

Sport Books Publisher2 Learning Objectives To describe muscle’s macro and micro structures To explain the sliding-filament action of muscular contraction To differentiate among types of muscle fibres To describe group action of muscles

Sport Books Publisher3 Types of Muscle The human body is comprised of 324 muscles Muscle makes up 30-35% (in women) and 42-47% (in men) of body mass. Three types of muscle: Skeletal muscle Smooth muscle Cardiac muscle

Sport Books Publisher4 A. Skeletal (Striated) Muscle Connects the various parts of the skeleton through one or more connective tissue tendons During muscle contraction, skeletal muscle shortens and moves various parts of the skeleton Through graded activation of the muscles, the speed and smoothness of the movement can be gradated Activated through signals carried to the muscles via nerves (voluntary control) Repeated activation of a skeletal muscle can lead to fatigue Biomechanics: assessment of movement and the sequential pattern of muscle activation that move body segments

Sport Books Publisher5 B. Smooth Muscle Located in the blood vessels, the respiratory tract, the iris of the eye, the gastro-intestinal tract The contractions are slow and uniform Functions to alter the activity of various body parts to meet the needs of the body at that time Is fatigue resistant Activation is involuntary

Sport Books Publisher6 C. Cardiac Muscle Has characteristics of both skeletal and smooth muscle Functions to provide the contractile activity of the heart Contractile activity can be gradated (like skeletal muscle) Is very fatigue resistant Activation of cardiac muscle is involuntary (like smooth muscle)

Sport Books Publisher7 d) myofibril c) muscle fibre b) muscle fibre bundle a) Muscle belly Components of skeletal muscle

Sport Books Publisher8 Muscle Fibres Cylinder-shaped cells that make up skeletal muscle Each fibre is made up of a number of myofilaments Diameter of fibre ( mm) Length of fibre (appr. 15 cm) Surrounded by a connective tissue sheath called Sarcolemma Many fibres are enclosed by connective tissue sheath Perimycium to form bundle of fibres Each fibre contains contractile machinery and cell organelles Activated through impulses via motor end plate Group of fibres activated via same nerve: motor unit Each fibre has capillaries that supply nutrients and eliminate waste

Sport Books Publisher9 Muscle Teamwork Agonist (prime mover): - the muscle or group of muscles producing a desired effect Antagonist: - the muscle or group of muscles opposing the action Synergist: - the muscles surrounding the joint being moved Fixators: - the muscle or group of muscles that steady joints closer to the body axis so that the desired action can occur

Sport Books Publisher10 Bending or straightening of elbow requires the coordinated interplay of the biceps and triceps muscles

Sport Books Publisher11 Contractile Machinery: Sarcomeres Contractile units Organized in series ( attached end to end) Two types of protein myofilaments: - Actin: thin filament - Myosin: thick filament Each myosin is surrounded by six actin filaments Projecting from each myosin are tiny contractile myosin bridges Longitudinal section of myofibril (a) At rest

Sport Books Publisher12 High microscope magnification of sarcomeres within a myofibril

Sport Books Publisher13 Contractile Machinery: Crossbridge formation and movement Cross bridge formation: - a signal comes from the motor nerve activating the fibre - the heads of the myosin filaments temporarily attach themselves to the actin filaments Cross bridge movement: - similar to the stroking of the oars and movement of rowing shell - movement of myosin filaments in relation to actin filaments - shortening of the sarcomere - shortening of each sarcomere is additive b) Contraction Longitudinal section of myofibril

Sport Books Publisher14 Contractile Machinery: Optimal Crossbridge formation Sarcomeres should be optimal distance apart For muscle contraction: optimal distance is ( mm) At this distance an optimal number of cross bridges is formed If the sarcomeres are stretched farther apart than optimal distance: - fewer cross bridges can form  less force produced If the sarcomeres are too close together: - cross bridges interfere with one another as they form  less force produced Longitudinal section of myofibril c) Powerful stretching d) Powerful contraction

Sport Books Publisher15 Contractile Machinery: Optimal muscle length and optimal joint angle The distance between sarcomeres is dependent on the stretch of the muscle and the position of the joint Maximal muscle force occurs at optimal muscle length (lo) Maximal muscle force occurs at optimal joint angle Optimal joint angle occurs at optimal muscle length

Sport Books Publisher16 Muscle tension during elbow flexion at constant speed

Sport Books Publisher17 Contractile Machinery: Tendons, origin, insertion In order for muscles to contract, they must be attached to the bones to create movement Tendons: strong fibrous tissues at the ends of each muscle that attach muscle to bone Origin: the end of the muscle attached to the bone that does not move Insertion: the point of attachment of the muscle on the bone that moves

Sport Books Publisher18 Muscle Fibre Types Slow twitch fibres: Slow Oxidative (Type I) Fast twitch fibres: Fast Glycolytic (Type IIb) Fast Oxidative Glyc. (Type IIb)

Sport Books Publisher19 A. Slow Twitch Fibres Suited for repeated contractions during activities requiring a force output of < 20-25% of max force output Examples: lower power activities, endurance events

Sport Books Publisher20 B) Fast Twitch Fibres Significantly greater force and speed generating capability than slow twitch fibres Well suited for activities involving high power Examples: sprinting, jumping, throwing

Sport Books Publisher21 The Muscle Biopsy Used to determine muscle fibre type 1. Injection of local anesthetic into the muscle being sampled 2. Incision of approximately 5-7mm is made in the skin and fascia of the muscle 3. The piece of tissue ( mg) removed via the biopsy needle is imbedded in OCT compound 4. The sample is frozen in isopentane cooled to –180C

Sport Books Publisher22 Muscle Biopsy

Sport Books Publisher23 The Histochemistry The biopsy samples are first sectioned (8-10 μm thickness) Sections are processed for myosin ATPase: Fast twitch fibres – rich in myosin ATPase (alkaline labile) Slow twitch fibres – low in myosin ATPase (acid labile) Sections are processed for other metabolic characteristics

Sport Books Publisher24 Nerve-Muscle Interaction Skeletal muscle activation is initiated through neural activation NS can be divided into central (CNS) and peripheral (PNS) The NS can be divided in terms of function: motor and sensory activity Sensory: collects info from the various sensors located throughout the body and transmits the info to the brain Motor: conducts signals to activate muscle contraction

Sport Books Publisher25 Activation of motor unit and its innervation systems 1.Spinal cord 2. Cytosome 3. Spinal nerve 4. Motor nerve 5. Sensory nerve 6. Muscle with muscle fibres

Sport Books Publisher26 Motor Unit Motor nerves extend from the spinal cord to the muscle fibres Each fibre is activated through impulses delivered via motor end plate Motor unit: a group of fibres activated via the same nerve All muscle fibres of one particular motor unit are always of the same fibre type Muscles needed to perform precise movements generally consist of a large number of motor units and few muscle fibres Less precise movements are carried out by muscles composed of fewer motor units with many fibres per unit

Sport Books Publisher27 All-or-none Principle Whether or not a motor unit activates upon the arrival of an impulse depends upon the so called all-or-none principle An impulse of a certain magnitude (or strength) is required to cause the innervated fibres to contract Every motor unit has a specific threshold that must be reached for such activation to occur

Sport Books Publisher28 Intra-muscle Coordination The capacity to apply motor units simultaneously is known as intra-muscle coordination Many highly trained power athletes, such as weightlifters, wrestlers, and shot putters, are able to activate up to 85% of their available muscle fibres simultaneously (untrained: 60%) Force deficit: the difference between assisted and voluntarily generated maximal force (trained: 10%, untrained: 20-35%)

Sport Books Publisher29 Intra-muscle Coordination cont. Trained athletes have not only a larger muscle mass than untrained individuals, but can also exploit a larger number of muscle fibres Athletes are more restricted in further developing strength by improving intra-muscular coordination Trained individuals can further increase strength only by increasing muscle diameter

Sport Books Publisher30 Inter-muscle Coordination The interplay between muscles that generate movement through contraction (agonists) and muscles responsible for opposing movement (antagonists) is called inter-muscle coordination The greater the participation of muscles and muscle groups, the higher the importance of inter-muscle coordination To benefit from strength training the individual muscle groups can be trained in relative isolation Difficulties may occur if the athlete fails to develop all the relevant muscles in a balanced manner

Sport Books Publisher31 Inter-muscle Coordination cont. High-level inter-muscle coordination greatly improves strength performance and also enhances the flow, rhythm, and precision of movement Trained athlete is able to translate strength potential to enhance inter-muscle coordination

Sport Books Publisher32 Muscle’s Adaptation to Strength Training Individual’s performance improvements occur through a process of biological adaptation, which is reflected in the body’s increased strength Adaptation process proceeds at different time rates for different functional systems and physiological processes Adaptation depends on intensity levels used in training and on athlete’s unique biological make-up Enzymes adapt within hours, cardiovascular adaptation within 10 to 14 days