This document discusses energy systems and muscle fiber types as they relate to crossfit. It shows that high intensity crossfit workouts rely more on anaerobic energy systems compared to longer endurance events. It also explains that muscle fibers exist on a continuum from slow-twitch to fast-twitch. Crossfit uniquely challenges athletes to recruit fast-twitch fibers even when fatigued. The document provides considerations for training untrained crossfit athletes and the attributes of elite crossfit athletes.

1. Energy
Systems
&
Muscle Fibers
type

2. Energy Systems
Overview

3. Maximum Rate of Energy
Production
Maximum Duration of Energy
Production

4. Old School …
Aerobic Anaerobic
200m 11% 89%
400m 23% 77%
800m 35% 65%
1500m 45% 55%
*800m/1500m = Fran/Helen WOD’s

5. New School…
Aerobic Anaerobic
200m 29% 71%
400m 43% 57%
800m 66% 34%
1500m 84% 16%
*800m/1500m = Fran/Helen WOD’s

6. % Aerobic Contribution
100
80
60
New
40 Old
20
0
200m 400m 800m 1500m

7. % Anaerobic Contribution
100
80
60
New
40 Old
20
0
200m 400m 800m 1500m

8. When does the Switch Occur?
15-30 Seconds

9. Muscle Fiber
Overview

10. Muscle Fibers
Best to think of Muscle Fiber type as a Continuum
• LEFT = Pure Slow Twitch
• RIGHT = Pure Fast Twitch
• Middle = Many Blends and Variations

11. Characteristic of Fiber Types
Slow Twitch Fast Twitch
-Recruitment is Slow -Recruitment is Fast
-Relaxation time is Slow -Relaxation time is Fast
-Force = Low -Force = High
-Fatigue Resistant = High -Fatigue Resistant = Low
- Cell = Aerobic Enzymes - Cell = Anaerobic Enzymes

12. Athlete Examples
Middle?
Slow Twitch Fast Twitch

13. How do we know what Fibers
we are Training???

14. Determining Factor = Force
More Force = More
Fast Twitch Fibers
Less Force =
More Slow Twitch
Fibers

15. How does this Relate to
Crossfit?

16. The Crossfit Problem…
Moderate to High Force
application over a broad
amount of time.

17. Endurance events like
Running or Cycling
when an athlete is
tired he/she can’t kick.
(Recruit FT Fibers)
Crossfit makes the
“tired” athlete Recruit
(FT) Fibers whether
they want to or not. At
the expense of time.

18. Considerations for Untrained
Novice Crossfit Athletes…

19. Body weight exercises could recruit
(FT) fibers which will make them go
anaerobic quicker.
-In this case, Athlete will need more
time to recover between WOD’s.
(Max Effort)

20. Fast explosive movements are an injury
precaution because athlete have not
established neural pathways to recruit the
necessary (FT) fibers.
- Remember (ST) Relaxation Rate
- Exercises Examples
- Down Hill Sprinting
- Eccentric/Rebounding Plyo’s

21. Weak Athletes could still be “Aerobic
Giants” a.k.a. have great Engines!
- Structurally they are too weak to exude the
power to show you!
- Remember “Structural changes happen
slower than metabolic.”

22. Must haves for the Elite Crossfit
Athlete…
- Absolute Strength
- Very High Percent of Dynamic to Absolute
Strength (FT Fibers)
- Great Aerobic Capacity with out
sacrificing Strength (Enzymatic Fight)
- High Level of Skill (Technique)
- Great Neural Pathways (Recruiting FT Fibers)

23. The End