1. Before contraction, ATP cleaved by myosin head, head is extended
2. TT complex binds with Ca to reveal actin active site
3. Myosin head binds to actin site
4. Power Stroke (cocked spring)
5. ADP and P- released from head, new ATP binds, head detaches
6. ATP cleaved by myosin head, head is extended
7. Cycle Repeats

1. Tend to keep the muscle in readiness for contraction and assure that muscle tension is produced and transmitted smoothly during contraction
2. Assure that the contractile elements return to their resting positions when contraction is terminated
3. Help prevent the passive over-stretch of the contractile elements when these elements are relaxed
4. Absorb energy proportional to the rate of force application and to dissipate energy in a time-dependent manner

1. Increase stimulation rate
2. Recruit more (and larger) motor units

Plank, wall squat, holding luggage

(No mech.work is performed; no movement is produced; stabilizes jt. position or posture; muscle work is performed; energy dissipated as heat; initial isometric phase to all dynamic contractions; greater tension than concentric due to the greater number of cross-bridges developed and activation of more motor units)

"up" phase of arm curl

(muscle force greater than resistance force)

"down" phase of arm curl, walking downstairs

(resistance force greater than muscle force; max. tension developed (cross-bridges); greater chance of producing DOMS (delayed-onset muscle soreness)

same velocity (no acceleration)

"slow and controlled" contractions

same muscle tension

*doesn't really exist due to changing leverage of the joints; selectorized machines attempt to match muscle force profiles using cams*

same external resistance

(must overcome inertial first)

End of optimal myosin-actin orientation

What is the third phase of a muscle activation vs. the length of the sarcomere? 

Active Tension from contractile proteins

Passive Tension from stretch of elastic components (the high levels are most apparent over two-joint muscles)

Total Length Tension Curve is a combination of both passive and active tension and varies considerably between muscles of different structure and function 

depends on the limb's relationship to the line of gravity vector.

Other forms of resistance depends on the limb's relationship to the line of resistance

they have an inverse relationship.

As velocity increases, force produciton decreases

Eccentric relationship not as smooth as concentric

can produce greater force at similar (negative) velocities

–  Greater average force produced per cross-bridge as they are pulled apart

–  A more rapid reattachment phase of cross-bridge formation

–  Passive tension produced by the elastic components 

sarcomeres in series, designed for velocity and excursion (proportional to length)

Ex: Sartorius

sarcomeres in parallel, designes for force production (proportional to CSA)

Ex: quadriceps

the sum of the cross-sectional area of its fibers

the cross-sectional area reflects the amount of active proteins available to generate a contradiction force rather than just the cross-sectional area of the muscle (different for fusiform vs. pennate)

The fibers that attach at 0 degrees (parallel) have ALL force transmitted to the tendon

Fibers that attach at an angle greater than 0 degrees have LESS force transmitted to the tendon

Pennate muscles produce greater force than fusiform muscles because they can fit more fibers into a given length of muscle

*So force production is increased even though less force is transmitted since physiologically cross-sectional area increases significantly*

• Increase in conduction velocity and frequency of stimulation and hence muscle force metabolism.
• Greater enzymatic activity of muscle metabolism (increasing efficiency of muscle contraction).
• Increased elasticity of collagen (enhancing extensibility of the muscle-tndon unit

1. Increase in blood flow such as during a warm-up
2. Heat production generated by metabolism, by the release of energy during contraction and by friciton of the contractile components

1. Lack of coordination of movement (Reduce accuracy control and contractile velocity)
2. Redistribution of loads in tissue

1. Smaller
2. More extensive blood vessel system
3. More mitochondria
4. Large amounts of myoglobin

1. Larger
2. Extensive SR for rapid release of Ca₂₊
3. Lots of glycolytic enzymes
4. Less extensive blood supply
5. Fewer mitochondria

Type I = Slow Oxidative (fatigue resistance)

Type IIA = Fast Oxidative Glycolytic (relatively fatigue resistant)

Type IIB = Fast Glycolytic (fatigues easily)

T/F: 

Type I Fibers.

Electrical Stimulation.

Aging process itself (ie. hormonal changes)

Disuse (ie. hypokinesis)

Other factors (ie. nutrition, pathology, medications)

• Inhibits the spindle effect (increases muscle contraction in response to stretch)
• Enhance the Golgi effect (inhibits contraction and enhances relaxation in response to an increase in muscle tension)
• Adds new sarcomeres in series