ENERGY STORES AND SOURCES
•ATP, glucose, and free fatty acids are stored in various
amounts, with ATP storage being sufficient for only 5
to 7 s of activity. Glycogen, the storage form of car-
bohydrate and a polymer of glucose, is found in both
liver and muscle tissue.
•Triglycerides, the storage form of lipids, consist of
three fatty acids and a glycerol backbone. Amount
and energy yields for glycogen (4 kcal/g) in liver and
skeletal muscle and triglycerides (9.4 kcal/g) in
skeletal muscle and adipose tissues are shown in
Table 8-3.
- Storing 1 g of glycogen requires at least 2 g of water,
thus the energy yield is less than half of what would
be expected from the weight: if there were 120 g of
glycogen, then 80 g would be water and the energy
yield would be 160 rather than 480 kcal.
•Type 2 fibers store more glycogen but less triglyc-
eride than Type 1 fibers. Proteins are not a storage
form of energy, and require catabolism of tissue for
energy.- The breakdown of glycogen to form glucose for
energy is called glycogenolysis and the process of
converting amino acids or lactate into glucose is
called gluconeogenesis.
BASIC DEFINITIONS IN EXERCISE
PHYSIOLOGYPULMONARY VENTILATION- The total volume of air moved into and out of the lungs
each minute, commonly called minute ventilation (VE),
is a function of tidal volume (VT) and respiratory rate
(fB). At rest, VE is between 5 and 7 L/min, whereas
during exercise it increases to between 60 and 180
L/min, depending on the health of the person (Fig. 8-3).
VT increases by expanding both inspiratory and expira-
tory volumes: these extravolumes are called inspiratory
and expiratory reserve volumes (IRV and ERV), respec-
tively. The increase in VT allows VE to increases five-
to tenfold during exercise. An increase in fB further aug-
ments VE.
MAXIMAL VOLUNTARY VENTILATION- Maximal voluntary ventilation(MVV), a measure of
maximum breathing capacity, is the volume of air
exchanged during repeated maximal respirations in a
specified time period (10 to 15 s). It is expressed as
38 SECTION 1 • GENERAL CONSIDERATIONS IN SPORTS MEDICINE
TABLE 8-3 Energy Stores for a 60-Kg Person with 15%
Body Fat
ENERGY SOURCE ENERGY (GRAMS) ENERGY (KCAL)
Liver and muscle 400–750 500–1000
glycogen
Glucose in body 15–20 60–80
fluids
Total carbohydrate 415–770 560–1080
stores
Subcutaneous adipose 9000 81,000
triglycerides
Intramuscular 150 1350
triglycerides
Total triglyceride 9150 82,350
stores
Total energy stores 9435–9920 82,970–83,430
FIG. 8-3 Tidal volume and breathing rate (left panel) and oxygen uptake and minute ventilation
(right panel) in response to progressive maximal treadmill exercise. Dotted line through VE in right
panel indicates departure from linearity.