Chapter 2 - Biomechanics of Resistance Exercise Flashcards
Origin and Insertion
O: proximal (doesn’t move; closer to body).
I: distal (moves; further from body)
Agonist
muscle most directly involved
aka Prime Mover
Antagonist
muscle that can slow down or stop a movement (opposite)
Synergist
muscle that assists indirectly in a movement.
Mechanical Advantage
Ratio of moment arm through which an applied muscle force acts to that through which a resistive force acts.
- 0+ = Fm < Fr to produce equal torque; advantage.
- 1.0= Fm > Fr to produce equal torque; disadvantage.
First Class Lever
MF and resistive force act on opposite sides of the fulcrum.
Ex. triceps ext.
Second Class Lever
MF and Fr act on same side of fulcrum, with MF acting through a moment arm longer than that of Fr.
Mechanical Advantage.
Ex. Calf Raise
Third Class Lever
MF and Fr act on same side of fulcrum, with MF acting through a moment arm shorter than that of Fr. Mechanical Disadvantage.
Ex. Bicep Curls
Patella and Mechanical Advantage
Patella increases MA of quads by maintain the quads tendon’s distance from the knee’s axis of rotation.
Absence of patella allows tendon to fall closer to knee’s center of rotation, shorting the moment arm
Moment Arm and Mechanical Advantage
Longer moment arm = more MA
Shorter moment arm = less MA
Ex. Biceps curl; moment arm length changes during the ROM. Shorter at full ext., longest at middle, and shortest at full curl.
Variations in Tendon Insertion
Tendons attach to bones.
Insertion further from joint = ability to lift heavier weights, but loss of max speed and reduced MF capability during faster movements.
Anatomical Planes
Sagittal (L,R)
Frontal (F,B,
Transverse (U,L)
Strength
Capacity to exert force
Positive Power
Precisely defined as the time rate of doing work.
Power (watts) = Work/Time (seconds)
Positive Work
Product of the force exerted on an object and the distance the object moves in the direction in which the force is exerted.
Work (Joules) = Force x Displacement (meters)
Negative Work and Power
All such “negative” power and work occur during eccentric muscle action (i.e. lowering weight or decelerating at the end of a rapid movement.
Angular Work and Power
Required for objects rotating about an axis or to change rotational velocity.
Angular Displacement
Angle in which an object rotates on a circular path.
Angle between starting ands final position.
Measured in radian (rad).
Angular Velocity
Object’s rotational speed. Measured in radians per second (rad/s).
Torque
Degree to which a force tends to rotate an object about a specified fulcrum, aka moment. Measured in newton-meters (N-m)
Rotational (Angular) Work and Power
Rotational Work = Torque x Angular Displacement
Rotation Power is same as linear power.
Strength v. Power
Although STR is associated wit slow and PWR with high velocities of movement, both reflect ability to exert force at a given velocity. (i.e. weightlifting has higher power component than powerlifting b/c of higher movement velocities with heavy weights.
Power is direct mathematical function of force and velocity.
Biomechanical Factors in Human Strength (8)
Neural Control Muscle Cross-Sectional Area Arrangement of Muscle Fibers Muscle Length Joint Angle Muscle Contraction Velocity Joint Angular Velocity Strength-to-Mass Ratio Body Size
Neural Control
MF is greater when: (a) more motor units are involved ini a contraction (recruitment), (b) the motor units are greater in size, or (c) the rate of firing is faster (rate coding).