運動營養學專題研究
Sport Nutrition
Chapter 3
Fuel sources during exercise
張振崗 教授
Jeukendrup A, Gleeson M. Sport nutrition: an introduction to energy
production and performance, 2nd Ed. Human Kinetics, 2010
1
2
3
Pathways of
energy
metabolism
Anaerobic production of ATP
capacity and rate
4
ATP resynthesis rate
Anaerobic and aerobic metabolism
5
6
Sources of Fuel During Exercise

Carbohydrate



Fat



Blood glucose
Muscle glycogen
Plasma FFA (from adipose tissue lipolysis)
Intramuscular triglycerides
Protein

Only a small contribution to total energy production
(only ~2%)


May increase to 5-15% late in prolonged exercise
Blood lactate

Gluconeogenesis via the Cori cycle
7
Energy stores in human body
8
Energy storage
9
Exercise Intensity and Fuel Selection

Low-intensity exercise (<30% VO2max)


High-intensity exercise (>70% VO2max)


Fats are primary fuel
CHO are primary fuel
“Crossover” concept


Describes the shift from fat to CHO metabolism
as exercise intensity increases
Due to:


Recruitment of fast muscle fibers
Increasing blood levels of epinephrine
10
Illustration of the “Crossover” Concept
Effect of Exercise Intensity on Muscle
Fuel Source
11
12
Energy
sources
during
different ex
intensity
Endurance training ↑fat oxidation
at same intensity
13
14
Contribution of protein as energy source
Glucose-alanine
cycle
15
Alanine output during different
ex intensity
16
Energy contribution of fuels in
different running speed
17
18
Exercise Duration and Fuel Selection


During prolonged exercise there is a shift
from CHO metabolism toward fat
metabolism
Increased rate of lipolysis 脂肪分解



Breakdown of triglycerides into glycerol 甘油
and free fatty acids (FFA) 游離脂肪酸
Stimulated by rising blood levels of
epinephrine
Fat metabolism requires longer time
19
Shift From CHO to Fat Metabolism During
Prolonged Exercise
20
Interaction of Fat and CHO Metabolism
During Exercise


“Fats burn in the flame of carbohydrates”
Glycogen is depleted during prolonged highintensity exercise



Reduced rate of glycolysis and production of
pyruvate
Reduced Krebs cycle intermediates
Reduced fat oxidation

Fats are metabolized by Krebs cycle
6 hr ex at
same
intensity:
energy
source shift
from CHO to
fat
21
22
4 hr ex at same
intensity:
energy source
shift from CHO
to fat
Effect of Exercise Duration on Muscle
Fuel Source
23