Energy

Systems

&

Muscle Fibers

type

Energy Systems

Overview

Ma

xim

um

Ra

te o

f En

erg

y

Pro

du

ctio

n

Maximum Duration of Energy Production

Old School …

Aerobic Anaerobic

200m 11% 89%400m 23% 77%800m 35% 65%1500m 45% 55%

*800m/1500m = Fran/Helen WOD’s

New School…

Aerobic Anaerobic

200m 29% 71%400m 43% 57%800m 66% 34%1500m 84% 16%

*800m/1500m = Fran/Helen WOD’s

% Aerobic Contribution

0

20

40

60

80

100

200m 400m 800m 1500m

New

Old

% Anaerobic Contribution

0

20

40

60

80

100

200m 400m 800m 1500m

New

Old

When does the Switch Occur?

15-30 Seconds

Muscle Fiber

Overview

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

Characteristic of Fiber Types

Slow Twitch

-Recruitment is Slow

-Relaxation time is Slow

-Force = Low

-Fatigue Resistant = High

- Cell = Aerobic Enzymes

Fast Twitch

-Recruitment is Fast

-Relaxation time is Fast

-Force = High

-Fatigue Resistant = Low

- Cell = Anaerobic Enzymes

Athlete Examples

Slow Twitch Fast Twitch

Middle?

How do we know what Fibers

we are Training???

Determining Factor = Force

Less Force =

More Slow Twitch Fibers

More Force = More

Fast Twitch Fibers

How does this Relate to

Crossfit?

The Crossfit Problem…

Moderate to High Force

application over a broad

amount of time.

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.

Considerations for Untrained

Novice Crossfit Athletes…

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)

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

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.”

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)

The End