PE 254 Measuring Musculoskeletal Fitness (Chapter 7)

Human Body Muscle Diagram

Behavioral Properties of the Musculotendinous Unit Behavioral properties of muscle tissue: ◦ Extensibility ◦ Elasticity ◦ Irritability ◦ Ability to develop tension Behavioral properties common to all muscle: ◦ Cardiac, smooth, skeletal

Extensibility and Elasticity Extensibility Elasticity Two components: ◦ Parallel elastic component (PEC) ◦ Series elastic component (SEC) Contractile component Visoelastic (Having flow-resistive as well as stretchy properties)

Irritability and the Ability to Develop Tension Irritability ◦ The ability to respond to electrical or mechanical stimulus. ◦ Response is the development of tension.  Not necessarily a contraction

Structural Organization of Skeletal Muscle Human body has approx. 434 muscles ◦ 40-45% of total body weight in adults ◦ 75 muscle pairs responsible for bodily movements and posture Muscle Fibers Motor Units Fiber Types Fiber Architecture

Muscle Fibers Contain: sarcolemma sarcoplasm nuclei mitochondria myofibrils myofilaments Sarcomere Z lines M line A band myosin filaments I band actin filaments H zone

Motor Units

Fiber Types Fast Twitch (FT) ◦ Type IIa ◦ Type IIb Slow Twitch (ST) ◦ Type I Peak tension reached in FT in 1/7 time of ST ST and FT compose skeletal muscles ◦ Percentages of each range from muscle to muscle and individual to individual.

Slow Twitch (Type I) The slow muscles are more efficient at using oxygen to generate more fuel (known as ATP) for continuous, extended muscle contractions over a long time. They fire more slowly than fast twitch fibers and can go for a long time before they fatigue. Therefore, slow twitch fibers are great at helping athletes run marathons and bicycle for hours. Fast Twitch (Type II) Because fast twitch fibers use anaerobic metabolism to create fuel, they are much better at generating short bursts of strength or speed than slow muscles. However, they fatigue more quickly. Fast twitch fibers generally produce the same amount of force per contraction as slow muscles, but they get their name because they are able to fire more rapidly. Having more fast twitch fibers can be an asset to a sprinter since she needs to quickly generate a lot of force. Type IIa Fibers These fast twitch muscle fibers are also known as intermediate fast-twitch fibers. They can use both aerobic and anaerobic metabolism almost equally to create energy. In this way, they are a combination of Type I and Type II muscle fibers. Type IIb Fibers These fast twitch fibers use anaerobic metabolism to create energy and are the "classic" fast twitch muscle fibers that excel at producing quick, powerful bursts of speed. This muscle fiber has the highest rate of contraction (rapid firing) of all the muscle fiber types, but it also has a much faster rate of fatigue and can't last as long before it needs rest.

Fiber Types Effects of training: ◦ Endurance training can increase ST contraction velocity by 20% ◦ Resistance training can convert FT fibers from Type IIb to Type IIa Elite athlete fiber type distribution does not significantly differ from untrained individuals Affected by: ◦ Age and Obesity

Recruitment of Motor Units CNS enables matching of speed and magnitude of muscle contraction to requirement of movement. Threshold activation ◦ ST activated first (low threshold) ◦ With an increase in speed, force, and/or duration requirement, higher threshold motor units are activated (FT fibers)

Change in Muscle Length with Tension Development Concentric ◦ Bicep shortening with the bicep curl (flexion) Isometric ◦ Body builders develop isometric contraction in competition Eccentric ◦ Acts as a breaking mechanism to control movement

Roles Assumed by Muscles Agonist ◦ Primary & Secondary Antagonist Stabilizer Agonists and Antagonists are typically positioned on opposite sides of a joint.

Muscular Strength, Power, and Endurance Muscular Strength Muscular Power Muscular Endurance Muscular Fatigue Effect of Muscle Temperature

Factors Impacting Force Production Torque: turning effect of an eccentric force ◦ T= Applied Force * Force Arm  Force arm is the perpendicular distance between the applied force and the axis of rotation Eccentric force: applied in a direction not in line with center of rotation of non- moving axis

Muscular Strength The ability of a given muscle group to generate torque at a particular joint. Two orthogonal components: ◦ 1) Rotary Component ◦ 2) Parallel to bone Derived from: ◦ amount of tension the muscles can generate moment arms of contributing muscles with respect to joint center.

Muscular Power The product of muscular force and the velocity of muscular shortening. The rate of torque production at a joint Max. power occurs at: ◦ approx. 1/3 max. velocity, and ◦ approx. 1/3 max concentric force Affected by muscular strength and movement speed

Muscular Endurance The ability to exert tension over a period of time. ◦ Constant: gymnast in iron cross ◦ Vary: rowing, running, cycling Length of time dramatically effected by force and speed requirements of activity. Training involves many repetitions with light resistance.

Muscular Fatigue Opposite of endurance Characteristics: ◦ Reduction in force production ◦ Reduction in shortening velocity ◦ Prolonged relaxation of motor units between recruitment Possible causes?

Modes of Exercise Isotonic: alternating concentric and eccentric muscle activation that moves a body part through an arc of motion against resistance Isokinetic: exercise that involves specialized equipment that provides "accomodating resistance" so that the joint moves at a constant angular velocity Isometric: muscle action that is performed against resistance at any point in a joint's range of motion, for periods of 5-10 seconds, and that produces no joint movement Plyometric: exercise that requires eccentric activation of muscles against a resistance, followed by a brief amortization period, followed by concentric activation

Overload Overload induces muscles to adapt, to increase their ability to generate force. Once muscles have adapted to overload, the overload stimulus must be increased to produce further training effects (progressive overload).

Effect of Muscle Temperature Increased body temperature, increases speed of nerve and muscle function Fewer motor units needed to sustain given load Metabolic processes quicken Benefits of increased muscular strength, power and endurance Key point: Be sure to warm-up!

Common Muscle Injuries Strains ◦ Mild, moderate or severe Contusions ◦ Myositis ossificans (A condition in which calcium, and eventually bone, become deposited in muscle; often the quadriceps) Cramps Delayed-Onset Muscle Soreness (DOMS) Compartment Syndrome (A painful condition caused by increased pressure within a muscle compartment)

Brzycki's equation to determine max load The Brzycki equation is as follows: Weight ÷ [ ( × Number of repetitions ) ]

Group Activities Muscular training for athletes for 2012 Summer Olympics: BoxingSoccerGymnastics VolleyballRowingWrestling Apply: Frequency, Intensity, Time, and Type(s)

Agonist muscles ◦ Primary & Secondary Antagonist muscles Stabilizer muscles

Video Segments qUw qUw fitness-2 fitness-2

Monday, October 12 th Please meet at the Fitness Lab (PE 2A) for muscular endurance/strength activities.