Factors affecting muscle strength Flashcards
muscle strength
is the ability of skeletal muscle to develop force for the purpose of providing stability and mobility within the musculoskeletal system so that functional movement can take place
examples of muscle strength
Capacity to exert force
Ability to do work against resistance
importance of muscle strength
activities of daily life (ADL)
Lifespan - high muscular strength = reduced risk of premature death
Sports - higher muscular strength = better performance and reduce risk of injury
where does the muscle strength come from
muscle tension
load
The force exerted on the muscle by the object
muscle tension
Force developed in a contracting muscle when the muscle acts on an object
active tension
Tension developed by the contractile elements of the muscle
passive tension
Tension developed by stretching the non-contractile elements of the muscle
Elasticity
contractile compenents contribute to muscle tension
myosin and actin overlapping
elastic compenents contribute to muscle tension
epimysium of muscle
tenons
torque
The capability of a force to produce rotation
moment =
Force x Perpendicular Distance from the line of action of the force to the centre of rotation of the object
first class lever
chin raise
fulcrum of chin raise
atlas and occipital bone of skull
effort of chin raise
neck pull posterior muscles of skull down
lead of chin raise
anterior skull is lifted
second class lever
calf raise
fulcrum of calf raise
joints at the ball of foot
effort of calf raise
calf muscles contract and lift muscle weight
lead of calf raise
body weight
third class lever
elbow flexion
effort of elbow flexion
bicep contract and pull forearm up
lead of elbow flexion
forearm and hand we lift
fulcrum of elbow flexion
elbow joint flexes and bicep contract
factors affecting muscle strength
Integrity of connective tissue and bone Type of muscle contraction Length of muscle Speed of contraction Number and size of motor units activated
muscle force will be inhibited by
Pain
Inflammation
Injury
Disease of the connective tissue or bone upon which the muscle acts
Direction of muscle forces wrt joint angle in a concentric movement
the same direction
Direction of muscle forces wrt joint angle in eccentric movement
the opposite direction
Source of force producing movement in concentric contraction
Muscle itself (muscle torque > load)
Source of force producing movement in isometric contraction
Muscle and load are equal and opposite (muscle torque = load)
Source of force producing movement in eccentric contraction
External load or gravity (muscle torque < load)
purpose of concentric contraction
To generate force against external resistance; to create movement against gravity
purpose of isometric contraction
To maintain stability
purpose of eccentric contraction
To control downward movement; to slow down a very fast movement
If muscle shortening (concentric contraction) is preceded by an eccentric muscle action, what does this mean? And why?
the resulting concentric action is capable of generating greater force. Because a stretch in a muscle increases its tension by storing potential elastic energy in the series elastic component of the muscle.
length tension relationship in short lengths
When a muscle has shortened to half its length, the filaments have exceeded their overlapping capability and fewer cross bridges can be formed.
length tension relationship in long lengths
When the muscle is lengthened > 20% beyond its resting length, cross bridges slip past one another and fewer cross bridges can be formed
length tension relationship in optimal length
Optimal length is slightly longer than resting length because
Contractile components are optimally producing tension (lots of cross bridges available)
Passive components are optimally storing elastic energy
Muscles create an active force which will:
Match the external load (object or gravity)
Adjust the speed of movement
in concentric action how does the velocity and force change?
In concentric action, velocity increases at the expense of a decrease in force.
In concentric action, velocity increases at the expense of a decrease in force. Why?
Because as the velocity of muscle shortening increases, the cycling rate of cross-bridges increases, leaving fewer cross-bridges attached at one time.
motor unit
a single motor neuron and all the muscle fibres it innervates
hennemann size principle
Smaller motor units are recruited first, then larger ones
Slower twitch muscle fibres are recruited first, then faster twitch fibres
rate coding
Muscle contracts by the summation of twitches
Rate coding means:
Higher frequency = higher force
how are skeletal muscle fibres classified
slow twitch (type 1) or fast twitch (type 2)
3 types of skeletal muscle fibres
Type I - Slow twitch oxidative (S) Type IIA (2a) - Fast twitch oxidative-glycolytic (FFR = fast fatigue resistant) (fast twitch) Type IIX (2b) - Fast twitch glycolytic (FF = fast fatiguing) (super fast twitch)
fusiform muscle
=> rapid shortening, greater ROM, less force
pennation muscle
slower velocity, less ROM, greater force and power (greater CSA)
