Muscle Physiology Flashcards
Energy - System Pathways
Three energy-producing systems:
Adenosine triphosphate-creatine phosphate (ATP-PC)
Glycolytic pathway
Oxidative pathway
All three pathways produce ATP, but they differ in terms of how much and how quickly.
During exercise these systems work concurrently in varying degrees, shifting reliance depending on the demands placed on the body.
Types of Muscles - Skeletal Muscles
Skeletal muscle tissue is striated in appearance. It is attached to bones by tendons and is used to move the body or keep the body in place. Skeletal muscles are voluntarily controlled by the somatic nervous system and contract when stimulated by nerve impulses.
Types of Muscles - Smooth Muscles
Smooth muscle is found in the walls of internal organs. These muscles are part of the autonomic nervous system, which means they operate outside of conscious control.
Types of Muscles - Cardiac Muscles
The walls of the heart are composed of cardiac muscle, whose cells can function independent of the brain’s control. Cardiac muscle moves blood through the cardiovascular system, delivering oxygen and nutrients and removing waste from the cells.
Skeletal Muscle Action - Agonist/Antagonist
Agonists, also known as “prime movers,” cause movement to occur through their own contraction.
Antagonists, on the other hand, oppose a specific movement by controlling it, slowing it down or returning a limb to its original position.
To propel the body forward during running, the hip extends via concentric contraction of the agonists, while the antagonists slow this movement and act to pull the leg forward.
Not all muscles are paired as agonists/antagonists.
Skeletal Muscle Action - Synergist
Synergist muscles stabilize and control muscle movements so that the range of motion is safe.
Synergist muscles also enhance stability and balance and reduce the load from the prime movers.
Working synergistically reduces the amount of work muscles need to do.
Skeletal Muscle Action - Fixator
Fixators are designed to stabilize a joint and allow people to isolate movements to a specific joint or area of the body.
Muscle contraction
Skeletal muscle contracts when a nerve impulse stimulates the muscle fibers of a motor unit to initiate a reaction between the actin and myosin filaments.
The higher the motor unit recruitment, the stronger the muscle contraction and force produced.
Motor unit = motor neuron + muscle fibers
Muscle Fibers - Type I Slow oxidative (SO) fibers
Type I fibers are known as “slow twitch.” They contain more mitochondria and have greater capacity for oxidative energy production. When recruited, Type I fibers produce less force and are more resistant to fatigue.
Most endurance athletes have an abundance of Type I fiber and rely heavily upon them for performance.
Muscle Fibers - Type IIa fast oxidative - glycolytic (FOG)
Type IIa fibers are known as “intermediate fast twitch” fibers because they exhibit characteristics of both Type I and Type IIb fibers. They have a high capacity to utilize both oxidative and glycolytic ATP energy systems. When recruited, they exhibit a great degree of force production and have a high resistance to fatigue.
Triathletes that compete at distances that require higher velocities or higher force production, such as sprint distances, may rely more on the function of this fiber type.
Muscle Fibers - Type IIb fast - twitch glycolytic fibers
Type IIb fibers are known as “fast twitch.” These fibers primarily use the glycolytic energy system for ATP production. When recruited, they have a very high force production; however, they fatigue easily.
As you can imagine, these fibers are found in abundance in sprint and power athletes.
Triathletes rely heavily on this type of fiber when sprinting during training or at the finish of a race.
Types of muscle contraction - concentric
While under tension, the muscle shortens.
Types of muscle contraction - eccentric
While under tension, the muscle lengthens.
Types of muscle contraction - isometric
While under tension, the muscle length does not change.
Force production
Eccentric muscle produces the most amount of force, but can also lead to greater muscular damage. Isometric contractions produce more force than concentric contractions because the force produced is equal to the load applied against it. Concentric is the least forceful because the muscular force applied is greater than the external load. Exercise that equally focuses on eccentric and concentric contractions can thus produce greater gains than concentric contractions alone.
