Exercise Metabolism
Chapter 4 pp 53-68

1. Rest-to-Exercise:
Anaerobic
“anaerobic”

2. Rest-to-Exercise:
Aerobic
Example....
Assume standing requires 15 ATP and 0.4 liters/min of oxygen
Assume running at 6 mph requires 100 ATP and 1.5 liter/min of oxygen
A person can go from standing to running 6 mph in a mater of seconds.
But, it takes 2-3 minutes for the oxygen requirement to go from 0.4 to 1.5 liters/min
Where does the ATP needed to run 6 m.p.h come from until adequate oxygen can be supplied?

Rest-to-Exercise:
The Oxygen Deficit
(anaerobic)
(aerobic)

3. Recovery
What needs to happen in recovery?
ATP-PCr system
P + Cr + energy
➡
PCr
Where does the energy comes from?
Glycolysis?
Lactic acid removal from muscle fiber

Lactic Acid Removal
Where ?
Heart and Type I Muscle Fibers
How ?
Lactic acid
➞
Pyruvic Acid
Pyruvic Acid
➞
Acetyl Co-A
Acetyl Co-A
➞
Krebs Cycle
(aerobic system)

Lactate as a Fuel During
Exercise
Slow twitch muscle fibers
Heart muscle
Liver via the Cori cycle

E.P.O.C
EPOC
• What does E.P.O.C. stand for note: oxygen consumption = energy
• What contributes to the excess oxygen consumption?
EPOC

(Used as a fuel)

4. Prolonged Aerobic
Exercise
Aerobic energy requires O2 oxygen demand
O2 transported via cardioplumonary system oxygen supply

Prolonged Aerobic Exercise
Deficit: O2 supply < O2 demand
Steady State Exercise
O2 supply = O2 demand
Heart rate? Breathing rate?

5. Measurement of Aerobic
Energy/Performance
Maximal oxygen uptake
Lactate threshold

Oxygen Uptake
Ventilation
(Liters of air per minute)
79% N
~17% O2
~4% CO2
13
79% N
20.97% O2
0.03% CO2

Oxygen Uptake (VO2)
79% N
20.97% O2
0.03% CO2
VO2
79% N
~17% O2
~4% CO2
14

Oxygen Uptake (VO2)
What does it measure?
How is it expressed?
VO2 ml/kg/min
VO2 liters/min

Maximum Oxygen Uptake
(VO2max)
VO2max
What is VO2max? What does it represent?

VO2max Values
Percentile
Men
90
50
10
Women
90
50
10
20-29
55.1
44.2
34.5
49.0
37.8
28.4
30-39
52.1
42.6
33.0
40-49
50.6
41.0
31.4
45.8
34.6
26.7
42.6
33.0
25.1
Source: ACSM
50-59
49.0
37.8
29.9
37.8
29.9
21.9
60+
44.2
34.6
26.7
34.6
26.7
20.3

* General Population, Female, Aged 20-29: 35-43 ml/kg/min
* General Population, Male, Aged 20-29: 44-51
* US College Track, Male: 57.4
* College Students, Male: 44.6
* Highest Recorded Female (Cross-Country Skier): 74
* Highest Recorded Male (Cross-Country Skier): 94

VO2max

Bjørn Dæhlie 96 ml/kg/min
Steve Prefontaine 84 ml/kg/min

What happens to pyruvate?
If adequate oxygen… pyruvate to acetyl CoA hydrogen to H2O
If inadequate oxygen… pyruvate and hydrogen to lactic acid
What happens to lactic acid levels as the exercise intensity increases?
Oxygen
2 .
2 .
1 .
1 .
Acetyl-CoA
Mitochondria
(Krebs cycle &
Electron Transport
Chain)

Lactate Threshold
Light to
Moderate
Exercise.
LA removed
Heavy Exercise.
LA accumulates
3 4 5 6 7 8 9 10
Speed (mph)

Lactate Threshold
The Lactate Threshold typically occurs between 50-
85% of Vo2max
What is significant about the intensity level at the lactate threshold?
3 4 5
7
8
Running Speed
9 10
6
VO2ma x
3 4 5
7
8
6

7. Fuel Utilization During Exercise

Measuring Fuel Utilization During
Exercise
•
•
Respiratory exchange ratio (RER or R)
R = VCO
2
/ VO
2
•
•
•
•
•
•
Fat (palmitic acid) = C
16
H
32
O
2
C
16
H
32
O
2
+ 23O
2
↔ 16CO
2
+ 16H
2
O + ATP
R = VCO
2
/VO
2
= 16 CO
2
/ 23O
2
= 0.70
Glucose = C
6
H
12
O
6
C
6
H
12
O
6
+ 6O
2
↔ 6CO
2
+ 6H
2
O + ATP
R = VCO
2
/VO
2
= 6 CO
2
/ 6O
2
= 1.00
It takes more
O2 to burn fats so the R value for fats will be lower.

Fuel Utilization During
Exercise
Carbohydrates and Fats (very little Protein)
Resting
Low Intensity
High Intensity
Max. Intensity
R
0.70
0.75
0.80
0.85
0.90
0.95
1.00
% Fat
99
83
67
50
33
17
1
% Carbs
1
17
33
50
67
83
99
High Intensity

Fuel Utilization During
Exercise
Which fuel is used more as the exercise
INTENSITY increases?
Why the shift towards carbohydrates?

Fuel Utilization During Exercise
What fuel is used more as the exercise DURATION increases?
Why the shift towards fats?

8. Fuels for Exercise

Sources of Carbohydrate During
Exercise
Muscle glycogen
Liver glycogen
Total of about 2,000 kcals (1.5-2 hrs)
Systems
Glycolysis
Lactic acid
Aerobic

Sources of Fat During Exercise
Adipose tissue
Triglycerides to fatty acids
Muscle cells
Total of 50,000-100,000 kcals
System: aerobic

Protein for Energy During
Exercise
Skeletal muscle
Amino acids and the Cori cycle
Why is protein not an optimal fuel source?

The Glucose-Alanine Cycle

Gluconeogensis
The Cori cycle and the Glucose-Alanine cycle
What do they have in common?
Gluconeogensis

Energy Related Fatigue
Glycogen depletion
Hypoglycemia