Sports Medicine: Just the Facts

CHAPTER 8 • BASICS IN EXERCISE PHYSIOLOGY 37

cycle. Other organic compounds can also enter the

TCA cycle. Free fatty acids(FFA) from triglycerides

are broken down into two-carbon acetyl fragments and

joined with CoA to form acetyl CoA. This process,

known as â-oxidation, can only occur under aerobic

conditions.

• Amino acids can also enter the TCA cycle after deami-
  nation/transamination and conversion into forms such as
  acetyl CoA and/or acetoacetate. The reduced coen-
  zymes, NADH and FADH 2 , formed during glycolysis
  and the TCA cycle, are shuttled to the electron transport
  chain within the mitochondria. There they are oxidized
  to NAD and FAD, respectively, and ATP is regenerated
  from ADP with 2.5 ATP/NADH and 1.5 ATP /FADH 2.
  The O 2 used is tightly linked to aerobic ATP production.


• One molecule of glucose going through the glycolytic
  pathway to lactate yields 2 ATP, whereas one mole-
  cule of glucose going through the aerobic pathway
  yields 30 ATP.

FIG. 8-2 A schematic of the energy systems in skeletal muscle: immediate, short term and long

term. SM: Sarcolemma, Glc: Glucose; FA: Free Fatty Acid; OMM: Outer mitochondrial membrane;

IMM: Inner Mitochondrial Membrane. (Designed by Mark Roseman, PhD.)

TABLE 8-2 Comparison of the Maximal Rates of Power
and Length of Time Power Can be Maintained for the
Immediate-, Short-Term, and Long-Term Energy Systems

MOLE OF TIME TO
ENERGY SYSTEMS ATP/MIN FATIGUE

Immediate: Phosphagen 4 5 to 10 s
(Phosphocreatine and ATP)
Short-term: Glycogen-lactic 2.5 1.0 to 1.6 min
acid (Glycolytic)
Long-term: Aerobic 1 Unlimited time