1. Fiber length (before contraction)
2. Previous contractions and rate of stimulation
3. Extent of fatigue (depletion of resources)
4. Thickness of fibers

1. ATP- a primary source (allows for a few seconds of contraction)
2. Phosphocreatine- Immediate backup, replenishes ATP
3. Muscle Glycogen (in muscle) and blood glucose (in blood)
4. Muscle and Blood fatty acids- reserves

ATP: Aerobic respiration Oxygen, Glucose or fatty acids, generates up to 36 ATP's per glucose

Phosphocreatine: Anaerobic respiration, fast contraction, no O2 needed, yields only 2 ATP per glucose

The muscle is unable to generate power or create tension
Sustained contraction of muscle over long time causes fatigue

Caused by a number of mechanisms

1. Central Factors: "feeling, perception" by CNS due to lactic acid- not true. muscle exhaustion
2. Peripheral: Depletion of ACH, ATP, and Glycogen stores
Accumulation of H+ or Pi levels, lactate, and high ECF K+

Two Types:
1. Unfused Tetanus- incomplete, bumps are closer together
Fiber partially relaxes

2. Complete/Fused Tetanus- due to a build up of calcium, is one big bump
A lot of inhibition and troponin, because when you contract so much, you rid of some of the elastic elements of the muscle
No relaxation, maximum tension

Varies depending on 1) location and 2) extent of training

the number of fibers we have is fixed early in life, and is regulated by myostatin and cytokine