Muscle Anatomy PE Theory 42 Read: 3, 6-13, Figures: 1.1, 1.3, 1.4a&b, 1.9, 1.10

Skeletal Muscle Skeletal muscles are muscles that are attached to bones to produce movement across joints Tendons attach the muscles to the bones allowing muscles to cause movement A muscle is made up of bundles of muscle fibers.

Skeletal Muscle Muscle belly Fasciculus Single Muscle Fiber

Muscle Fibers Type I - Slow Twitch Fibers –High aerobic capability for endurance –Lower contractile force capabilities Type II- Fast Twitch Fibers –High glycolytic capability for strength & power –High contractile force capabilities

Muscle Fiber Types Type I & II fibers very person to person Genetic (choose parents wisely) No differences in fiber type for men & women Elite Athletes Can A Type I change & become a Type II?

X-Section of Muscle Fibers Each person has different genetically determined strength, power, and endurance capabilities

Motor Unit Motor Unit- a motor neuron & all the muscle fibers it stimulates The basis of muscle stimulation Composed of either all type I or type II Fibers are spread out within a muscle

Motor Units When a muscle moves, those motor units that are not activated do not generate force; they move passively through the range of motion. The size of motor units varies: –Human eye- 10 fibers to a motor unit –Quadriceps- 450 or more fibers to a motor unit

Size Principle Motor units are recruited from the smallest to the largest based on the force demands placed on the muscle Low threshold units High threshold units

Size Principle Lifting heavy resistances will start with recruiting low threshold motor units first, and progressively move up the line until enough motor units are recruited to produce the needed force. The process is rapid. If only a low resistance is used, the largest motor units will no be recruited

Size Principle Selective activation of motor units & difference in size of motor units allow for graded force production More precise control of body movements

All or None Law When a specific motor unit reaches its threshold level for activation, all of the muscle fibers in that motor unit are activated fully If the threshold is not reached, then none of the muscle fibers in that motor unit is activated

All or None Law If one motor unit in a muscle is activated, that muscle produces only a very small amount of force If several motor units are activated, muslce produces more force If all motor units in a muscle are activated, maximal force is produced by the muscle

Muscle Activation Only the motor units that are actively recruited during an exercise produce force & subsequently are subject to the adaptations from that exercise

More on the Size Principle Very High Velocity movements are an exception The Type II’s are recruited first to allow faster movement, skipping type I activation Ensures low-threshold motor units are pred. Recruited for lower-intensity (endurance) activites, and Higher-threthold units for high force and power activites

To Build Strength In order to recruit Type II Fibers and receive a training effect in these fibers, the exercise must consist of heavy loading or high power output. Body position change (vary the exercise)can change the order of recruitment and different muscle fibers can be recruited