KNES 455G Chapter 4 Essentials-audio part 3

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Angular Velocity and Force:

Angular Velocity and Force

Types of Muscle Action:

Types of Muscle Action Eccentric- a muscle action in which the muscle lengthens because its contractile force is less than the resistive force. Concentric- a muscle action in which the muscle shortens because its contractile force is greater than the resistive force Isometric – muscle length doesn ’ t change because contractile force=resistive force

Strength to Mass Ratio:

Strength to Mass Ratio For athletes the relationship of strength to body mass is critical for movements that require lifting of the body or accelerating the body.

Body Size and Strength:

Body Size and Strength Mass of a muscle is related to its volume (3 rd order) Strength is related to its cross section area (2 nd order) Therefore strength does not increase directly proportional to mass. Smaller athletes will tend to have higher strength to mass ratios However; larger athletes have greater momentum which may be a critical element to success in certain sporting events.

Sources of Resistive Force:

Sources of Resistive Force Gravity – source of resistance for most all resistance exercises (barbell based or machine based) Exception would be elastic resistance supplied via tubing or bands and fluid resistance (surface drag and form drag)

Machine Resistance vs. Free Weights:

Machine Resistance vs. Free Weights Advantages Safety Design Flexiblity Ease of Use Disadvantages Doesn ’ t provide whole body training Doesn ’ t provide simulation of real-world activities


Inertia When a barbell or weight stack is accelerated it provides inertial force in addition to the resistive force of gravity. Can act in any direction, not just downward as with gravitational force.


Acceleration Generally at the beginning of a lift the agonist produce greater force than resistive in order to accelerate the bar. Towards the end of the lift the muscles will produce less force than resistive in order to allow the bar to negatively accelerate towards the end of the range of motion.


Friction F R =k*F N K is the coeffienct of friction, this varies based upon the surfaces interacting, and also varies from the initiation of movement, to constant movement.

Friction Force:

Friction Force Always in opposition to the applied force Examples: cycle ergometer where resistance is supplied by a belt strapped around the flywheel.

Back Injury:

Back Injury Force exerted on the upper body while standing must be transmitted through the vertebral column to the leg and ultimately the ground. The lower spine is particularly susceptible to injury, 85-90% of injuries to the back occur here.

Shape of the Back:

Shape of the Back Kyphotic – the vertebral column is naturally s-shaped, slightly rounded During lifting it has been determined A flat back is superior to a rounded back (i.e. Rounded forward) Lordotic back (slightly arched) found superior to a rounded back for injury protection, and allows muscles in the lower back to exert higher forces.

Valsalva Maneuver and Lifting Belts:

Valsalva Maneuver and Lifting Belts Some increase intra-abdominal pressure is helpful to stabilize the lower spine during weightlifting exercises such as the squat While the valsalva maneuver accomplishes this if the glottis is closed then it also increases pressure in the chest cavity compressing the heart. This can result in lack of sufficient blood flow (fainting) Safest way is to keep the airway open, however, more advanced athletes may choose to use the valsalva.

Valsalva Maneuver and Lifting Belts:

Valsalva Maneuver and Lifting Belts Some increase intra-abdominal pressure is possible with the use of properly worn weight lifting belt. However, if all lifts are performed with a belt, the ability of the body to develop in such a way as to protect the back will be hindered.

Other Joints of Concern:

Other Joints of Concern Shoulder Joint: given its range of motion this joint is particularly susceptible to injury. Knee joint: located between two long levers and thus subject to great force, also shearing forces and torque supplied through interaction with the ground.

Principle of Specificity:

Principle of Specificity Train in a motion pattern as near to that as the actual sporting event as possible. Key concept to proper design of resistance training. Involves not losing sight of the end goal of the training

Examples of Motions:

Examples of Motions

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