Muscle as a skeletal mover and
force modulator
FAIZAN ZAFFAR KASHOO
Syllabus for the 7th week
 Muscle as a skeletal mover force modulator
 Muscle tension.
 Muscle insufficiency
 Modulating force through concentric or eccentric
activation: force-velocity relationship.
Motor unit
 Motor unit is composed of a single motor nerve and
the muscle fibers it supply.
 If more number of motor units are recruited then the
muscle contraction will be stronger.
Motor point
 Entry of nerve into muscle is known as motor point.
 Normally located between upper 2/3rd and lower
1/3rd of a muscle.
Muscle tension
Active Muscle
tension
Contractile
elements
Muscle tension
Passive Muscle
tension
Noncontractile
elements
Muscle tension
 Muscles have the important ability to generate
tension.
 Muscle tension is composed of tension in active and
passive elements of muscle.
Passive tension
 Refers to tension in parallel elastic components of
muscle.
 These parallel components add to the tension when
the muscle is lengthen and become slack when the
muscle is shortens.
 These are connective tissue covering of muscle
example: Epimysium, Perimysium, fascia etc
Active tension
 Refers to tension produced by the contractile
elements of muscle.
 Tension generated because of cross bridge formation
between thin and thick filaments.
Factors affecting muscle tension
 Neural factors
 Mechanical factors
Neural factors
 Frequency of motor unit firing.
 Size of the motor unit.
 Number of motor units.
Mechanical factors
 Mechanical factors can better be explained through
 Isometric length-tension relationship.
 Force-velocity relationship.
 Physiological cross-sectional area of muscle.
Isometric length-tension relationship
Isometric length-tension relationship
 Short length…………………..less muscle tension
 Long length…………………….less muscle tension
 Optimal length………………….maximum tension
 Reason: maximum number of cross bridge formation.
Force-velocity relationship
Force-velocity relationship
 Velocity increase……………..tension decrease
 Velocity decrease…………….tension increase
 Maximum tension can only be generated with
eccentric contraction.
Physiological cross sectional area of muscle
 Larger muscle produce more tension than smaller
muscles.
Muscle insufficiency
 Limitations of a muscle
Classification of Muscle Insufficiency
Muscle
insufficiency
Passive
insufficiency
Active
insufficiency
tension in
antagonistic
muscle
Exhaustion
in agonistic
muscle
Muscle force Modulation
 Manipulation of number of motor units recruited in
the muscle in order to generate an appropriate
amount of force.
Error Correction mechanism by Brain
Brian gives orders
Basal ganglia (copy of command)
Cerebellum (copy of command)
Brain stem (original command)
Spinal cord Original command)
Peripheral nerve
Muscle contraction
Activation of sensory receptors on joint, skin and muscle
Information about movement carried
by sensory nerve