Skeletal Muscle

1
Skeletal Muscle

• State possible sources of fatigue
• Distinguish the different muscle fiber types.

2
Origins of Localized Muscle Fatigue
SITES OF THE SOURCES OF FATIGUE
3
Origins of Localized Muscle Fatigue
Depletion Theory of Fatigue
Fatigue results from the depletion of metabolites
necessary for energy production
Glucose
Oxygen
ADP or CP
Reaction Enzymes
4
Origins of Localized Muscle Fatigue
Accumulation Theory of Fatigue
Lactic Acid and free H
K
NH3
5
Skeletal Muscle Fiber Types

• innervating nerve is primary determinant of fiber
  type during development
• a motor unit is composed of homogenous fibers
• all human muscles contain mixture of three
  general fiber types
• slow twitch (ST, oxidative, red)
• fast twitch (FTa, fast-oxidative, red)
• fast twitch (FTb, glycolytic, white)

6
Time Course of Contributions from Different
Energy Sources
fast twitch glycolytic (white)
slow twitch oxidative (red)
Oxidative
7
Fiber Type Characteristics
Performance characteristics affected by

• Ca2-ATPase
• myosin ATPase speed
• aerobic capacity (mitochondria, myoglobin, blood
  supply, fatigue resistance)
• anaerobic capacity (glycolytic enzymes)

8
Muscle Movements Not all force results in
movement.

• Isotonic - (same force), muscle fibers create a
  force that moves a load. Muscle shortens or
  lengthens.
• Isometric - (same distance), muscle fibers create
  changing force but does not move a load. Muscle
  length doesnt change. Tendon collagen stretches
  out.
• concentric develops tension while shortening
• eccentric develops tension while lengthening
• (most muscle actions are a combination of these)