Muscle Physiology KINE 4396/5390 Strength and Conditioning Christopher Ray, PhD, ATC, CSCS
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Transcript of Muscle Physiology KINE 4396/5390 Strength and Conditioning Christopher Ray, PhD, ATC, CSCS
Muscle Physiology
KINE 4396/5390 Strength and ConditioningChristopher Ray, PhD, ATC, CSCS
Muscle Physiology
KINE 4396/5390 Strength and ConditioningChristopher 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 EndomysiumThree Types of Connective Tissue:Epimysium, Perimysium, and Endomysium
Three Arrangements of Muscle FibersThree 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 UnitA 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 MuscleContraction 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 MuscleContraction of a Myofibril: Partially Contracted Muscle
Contraction of a Myofibril: Completely Contracted MuscleContraction 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
• 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