Muscle Physiology
KINE 4396/5390 Strength and Conditioning
Christopher Ray, PhD, ATC, CSCS
Objectives
Anatomy of Skeletal Muscle
Muscular contraction
Muscle Fiber Types/Recruitment
Muscle action
Force production
Three Types of Connective Tissue:
Epimysium, Perimysium, and Endomysium
Three Arrangements of Muscle Fibers
Fibers parallel
to tendon
Unipennate
muscle
Bipennate
muscle
Fiber Pennation
• In a pennated muscle not all of the force
generated in the muscle fiber is delivered to the
tendon.
• Pennated muscles usually compensate for this
disadvantage by increasing the cross-sectional
area.
• Pennated muscles do not move a joint through
as large of ROM as do unipennate muscles.
A Motor Unit
• All muscle fibers of a
motor unit contract
together
• Connects via a
neuromuscular junction
– Each cell has 1
– Motor Neuron has many

The discharge of an action potential from a
motor nerve signals the release of calcium from
the sarcoplasmic reticulum into the myofibril,
causing tension development in muscle.
Contraction of a Myofibril: Stretched Muscle
•I-bands are Actin in two adjacent sarcomeres
•A-bands are Myosin
•During contraction the H-zone and I-bands decrease.
Contraction of a Myofibril:
Partially Contracted Muscle
Contraction of a Myofibril:
Completely Contracted Muscle
Contraction of a
Myofibril:
Stretched
Muscle
Contraction of a
Myofibril:
Completely
Contracted Muscle
H-Zone and I-band
shrink
Sliding Filament Mechanism/Theory
• Resting Phase
– Little Ca++ is present so few X-Bridges attached.
• Excitation-Contraction Coupling Phase
– Stimulus spreads thru T-Tubule
– SR releases Ca++
– Ca++ binds with Troponin exposing bind site on Actin
– Myosin binds with Tropomyosin
• Contraction Phase
– ATP downgraded to ADP + P
– Myosin arm does work on actin
• Recharge Phase
– Pick up new ATP
– Myosin head rotates backward
• Relaxation Phase
– Ca++ is pumped back into SR

Calcium and ATP are necessary
for myosin cross-bridge cycling
with actin filaments.

Type II, or fast-twitch, muscle fibers are
capable of developing higher forces than
Type I, or slow-twitch, muscle fibers—
especially at higher velocities of muscle action.

The number of cross-bridges
that are attached to actin filaments
at any instant in time dictates the
force production of a muscle.
Force Production & Factors influencing Force
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Motor Unit Recruitment
Preloading [holding a wt tightens up the muscles elastic structures].
Cross-Sectional Area
– Increasing the cross-sectional area increases strength
Velocity of Shortening
Angle of Pennation
Sarcomere and Muscle Length
Prestretching (Stretch-Shorten Cycle)
– Eccentric contraction followed by an immediate concentric contraction
[Plyometrics]
Exercise-Induced Muscle Damage (DOMS)
Older Muscle
– Sarcopenia (reduced muscle size & strength with age)
Muscle Fiber Type
– Type I (SO) aerobic fiber, low force, slow rise time
– Type IIa (INT) anaerobic fiber, high force, shorter rise time
– Type IIb (FT) anaerobic fiber, very high force, fastest rise time

Many factors may affect rate of cross-
bridge cycling and thus force, including neural
activation, calcium concentration, myosin
ATPase activity, preloading, prestretch, muscle
fiber type and ultrastructure, fatigue through a
variety of mechanisms, and number of
contractile components (myosin and actin) in
parallel.
Improving Force Production
• Use preloading during training to develop strength early in
ROM.
• Accomodating resistance apparatus (hydraulic, isokinetic) do not
load the muscle prior to contraction.
• Increase cross-sectional area of muscle by using moderate
resistance (65-80%) for max or near max # of reps.
• When overloading eccentrically use heavy resistance.
• When training for explosive concentric use light resistance.
• Prestretch a muscle before concentric to enhance force
production.
• Incorporate rest days into training cycle to avoid training with
DOMS and allow muscle time to repair.
Questions
• In an attempt to increase his 1 rm bench max;
George increased his resistance and added
negatives. He complains of increased soreness 48
hrs later. What is the soreness called? What is the
cause?
• What is occurring
– Resistance is greater than muscle force
– Resistance and force is equal
– Resistance is less than muscle force