Elite Physique The New Science of Building a Better Body

40 Elite Physique
keeping your organs and blood vessels running on autopilot. Skeletal muscle is
the contractile tissue that produces voluntary action and reflex action. Since this
book is about building a better physique and performance, our focus is on the
actions of skeletal muscle (see figure 3.1). So for the rest of this book, the word
muscle will relate specifically to skeletal muscle.
Your speed, power, and endurance rely heavily on the type of fibers that
make up your muscles. Humans have three primary types of muscle fibers: type
I, type IIa, and type IIx. Type I slow-twitch fibers are the main fiber type for
an activity that can be sustained for long durations at a low intensity, such as
walking or jogging for 30 minutes. Type IIa fast-twitch fibers work with type I
fibers during a moderate-intensity activity such as climbing 10 flights of stairs or
walking up a long hill. Type IIx fast-twitch fibers come into play mainly during
short, quick bursts of high-intensity activity such as a maximum vertical jump
or heavy squat.
Trapezius
Deltoid
Pectoralis major
Biceps brachii
Rectus abdominis
Brachialis
External oblique
Brachioradialis
Finger flexors
Infraspinatus
Teres major
Triceps brachii
Latissimus dorsi
Finger extensors
Adductor longus
Gracilis
Sartorius
Rectus femoris
Vastus lateralis
Vastus medialis
Tibialis anterior
Gluteus maximus
Semitendinosus
Biceps femoris
Semimembranosus
Gastrocnemius
Soleus
a
b
FIGURE 3.1 Human muscle system: (a) front view and (b) rear view.
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