# KNES 455G Chapter 4 Essentials-audio part 2

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## Presentation Transcript

### Special Joints:

Special Joints Many joints in the body do not have a true hinge, the axis of rotation changes during movement. Example would be the knee, however, the patella is in place to keep the quadriceps muscle from getting to close to the axis of rotation.

### Changes in Moment arm:

Changes in Moment arm

### Changes in Moment Arm:

Changes in Moment Arm

### Changes in Tendon Insertion:

Changes in Tendon Insertion

### Planes of the Body:

Planes of the Body

### Human Strength and Power:

Human Strength and Power Acceleration: change in velocity per unit time No such thing as deceleration, only negative acceleration. Force: equals mass times acceleration F=ma

### Human Strength and Power:

Human Strength and Power Human Strength: the maximal force that a muscle or muscle group can generate at a given speed. Work: product of force and distance W=Force x distance (joules) Power: Work done over time Power= Work/Time (watts)

### Calculate the Work and Power:

Calculate the Work and Power An athlete lifts a 225lbs bar performing a powerclean a distance of 1.75meters to the shoulders in 0.5 seconds. 225lbs x 4.448 = 1000.8 Newtons Work equals 1000.8Newtons*1.75 meters=1751.4 Joules (J) Power equals 1751.4J/0.5s = 3502.8 Watts

### Rotational Motion:

Rotational Motion Angular displacement: Angle an object rotates through in radians (1 radian equals 180°, so 2 radians equals one full rotation) Angular velocity: equals angular displacement divided by time (radians per second) Torque: product of newtons and length of the moment arm (Nm) Work = Torque*Angular Displacement

### Neural Control:

Neural Control Neural control affects the maximal force output of a muscle by determining which and how many motor units are involved in muscle contraction.

### Rate Coding:

Rate Coding Modulation of the rate of firing of motor units in order to affect the force production. The combination of which motor units are active and rate coding allow the CNS to control the force produced during an action.

### Muscle Cross Section:

Muscle Cross Section A muscle produces force in proportion to its cross sectional area. Logical, as this would relate to the amount of contractile tissue in the muscle.

### Arrangement of Muscle Fibers:

Arrangement of Muscle Fibers Pennate muscle: fibers that align obliquely with the tendon, creating a featherlike arrangement. The angle of pennation is defined as the angle between the muscle fibers and the line between the origin and insertion. There are many pennate muscle in the body, the majority have pennation angles < 15° Pennation angle does not remain the same during contraction, it increases as the muscle shortens

### Series vs. Parallel:

Series vs. Parallel Muscle with greater angles of pennation have more sacromeres in parallel and less in series. This leads to greater ability to produce force but lesser ability to generate high shortening velocities.

### Myosin Actin overlap:

Myosin Actin overlap