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