2004 USA Cycling 1st Biannual International Cycling Summit, Colorado Springs, CO.

1. “The science of exercise
and
the art of coaching”

2. Outline for talk
1.
Brief review of energy systems
2.
Determinants of endurance performance
3.
Muscle fiber type and recruitment
4.
Energy systems part II: what they didn’t teach you in Ex. Phys. 101
5.
Application to interval training

3. Adenosine triphosphate (ATP):
the “energy currency” of cells
ATP
ADP + Pi

4. Resynthesis of ATP: three energy systems
• Phosphagen system:
PCr + ADP
Cr + ATP
ADP + ADP
ATP + AMP
• Non-aerobic glycolysis:
glucose
2 lactate + 2H+ + 2ATP
• Aerobic metabolism:
glucose + 6O2
6CO2 + 6H20 + 36ATP
palmitic acid + 23O2
16CO2 + 16H20 + 130ATP

5. Three energy systems: relative contributions
From: Gastin PB. Energy system interaction and relative contribution during maximal exercise. Sports Med 31:725, 2001

6. VO2, heart rate, lactate, and RPE vs. power
VO2
Blood lactate
RPE
Heart rate
VO2 (L/min), lactate (mMol/L),
or RPE (U)
180
8
160
7
6
140
VO2max
120
5
100
4
80
3
OBLA
2
60
40
Lactate threshold
1
0
20
0
0
50
100
150
200
250
Power (W)
300
350
400
450
HR (beats/min)
9

7. Importance of LT
From: Coyle EF et al. Physiological and biomechanical factors associated with elite endurance cycling performance. MSSE 23:93, 1991.

8. VO2 vs. power (economy/efficiency)
5
y = 0.0112x + 0.4543
R2 = 0.9967
VO2 (L/min)
4
y = 0.0106x + 0.4575
R2 = 0.9975
3
2
1
0
0
50
100
150
200
Power (W)
250
300
350
400

9. Effect of efficiency on performance
From: Horowitz JF, Sidossis LS, Coyle EF. High efficiency of type I fibers improves performance. Int. J. Sports Med. 15:152, 1994.

10. Human skeletal muscle fiber type characteristics
Type I
Type IIa
Type IIb(x)
Size of muscle fiber
Smallest
Larger
Largest
# of fibers in motor unit
Smallest
Larger
Largest
Size of alpha motor neuron
Smallest
Larger
Largest
Order of recruitment
First
Next
Last
Force at zero velocity
(per unit area)
Same
Same
Same
Speed of contraction
Slowest
Faster
Fastest
Force/power at velocity
greater than zero
Lowest
Higher
Highest
PCr content
Lowest
Higher
Highest
Glycolytic enzyme activities
Lowest
Higher
Highest
Glycogen content
Lowest
Higher
Highest
Triglyceride content
Highest
Lower
Lowest
Mitochondrial enzyme
activities
Highest
Lower
Lowest
Capillarization
Highest
Lower
Lowest
Fatigue resistance
Highest
Lower
Lowest

11. Factors affecting fiber type recruitment
1. Exercise intensity
2. Exercise duration
3. Cadence?

12. Fiber type recruitment as a function of intensity
% fibers recruited at
onset of exercise
100
Total
80
60
Type I
40
Type IIa
20
Type IIb
0
25
50
75
100
% of VO2max
From: Vollestad NK et al. Effect of varying exercise intensity on glycogen depletion in human muscle fibers. Acta Physiol Scand 125:395, 1985.

13. Energy systems part II:
What they didn’t teach you in
Exercise Physiology 101

14. Three energy systems: relative contributions
From: Gastin PB. Energy system interaction and relative contribution during maximal exercise. Sports Med 31:725, 2001

15. Three energy systems: absolute contributions
From: Gastin PB. Energy system interaction and relative contribution during maximal exercise. Sports Med 31:725, 2001

16. Three energy systems: all-out vs. constant intensity
From: Gastin PB. Energy system interaction and relative contribution during maximal exercise. Sports Med 31:725, 2001

17. Half-time of PCr resynthesis

18. Half-lives of physiological responses
Power (force and/or velocity)
(0 s)
Heart rate/cardiac output:
~25 s
Sweating:
~25 s
VO2:
~30 s
VCO2:
~45 s
Ventilation:
~50 s
Temperature (core):
~70 s

19. Metabolic response to “micro” intervals

20. Energy metabolism during 30 s sprints
mmol of ATP
1000
Lactate production
PCr breakdown
Aerobic metabolism
750
59%
500
21%
16%
15%
250
63%
26%
0
1
2
3
Sprint bout number
From: Putman CT et al. Skeletal muscle pyruvate dehydrogenase activity during maximal exercise in humans. Am J Physiol 269:E458, 1995.

21. Analysis of different interval training sessions
• LT intervals: 2 x 20:00/5:00
• VO2max intervals: 6 x 5:00/2:30
• LT intervals: 8 x 5:00/1:00
• Anaerobic capacity intervals: 10 x 1:00/3:00

22. LT intervals: 2 x 20:00/5:00

23. VO2max intervals: 6 x 5:00/2:30

24. LT intervals: 8 x 5:00/1:00

25. Anaerobic capacity intervals: 10 x 1:00/3:00