PTHY 6401 Kinesiology I
Read Neumann Ch 1 pgs 18-20, Ch 3 pgs 52-60
Common Characteristics
 Excitability - receives & responds to nerve impulses
 Contractility - can shorten, thicken & generate force
 Extensibility - can be stretched
 Elasticity - returns to original shape after contraction or stretch
Skeletal Muscle Composition
 Basic unit - Muscle cell (fiber); can be up to 70 cm long o bound together to form a fascicle o fascicles bound together to form entire muscle o layer of tough connective tissue surrounds each “level” o this tough tissue extends beyond the muscle as a tendon
Terminology of Muscle Action
 Prime mover - contributes the most to the movement
 Synergist - assists the prime mover
 Agonist - same as prime mover
 Antagonist - opposes the agonist
 Agonist/Antagonist Patterns o flexors / extensors o adductors / abductors o medial / lateral rotators
Terminology of Muscle Contraction
 3 Types of skeletal muscle contraction o Isometric - “no movement”
 equal opposition of agonist/antagonist OR
 immovable weight o Concentric - shortening contraction of muscle with “expected” osteokinematic motion o Eccentric - lengthening contraction of muscle for “controlling” the opposite osteokinematic motion; such as controlled lowering of forearm against gravity (brachialis)
Muscle Contraction related to Exercise
 Isometric exercise o no movement (immovable weight or end of AROM) o isometric contraction
 Isotonic exercise o “same weight”, ex. Free weights o muscle contraction force varies as direction of object movement changes relative to the gravity line o speed of movement can vary o concentric or eccentric contractions
 Isokinetic Exercise o Accommodating / variable resistance
 Muscle force production can stay at max because the machine will accommodate to the varying force output
 “same speed of movement”
 concentric and eccentric contractions
 Why does muscle force production vary at different parts of the AROM??

PHYSICAL FACTORS IMPACTING MUSCLE FORCE PRODUCTION o Age o Gender o Speed of Contraction o Type of Contraction o Length - Tension Relationship
AGE
 Strength peaks between age 20 & 40 years of age o with aging comes a decrease in the number of muscle fibers (results in decreased mass & strength)
 Loss of muscle fibers & ms mass by 6th decade of life
 Fiber type changes: less Type II
GENDER
 males have greater strength than females after onset of puberty
 greatest difference in muscle strength between genders is ages 30 - 50.
 Differences due primarily to greater muscle mass o males can have up to 50% more muscle mass than females. Male and female muscle produce the same amount of force per cross-sectional area.
SPEED OF CONTRACTION
With concentric contractions, maximal force production decreases with increasing speed of contraction
(ie. force production decreases with faster movement)
TYPE OF CONTRACTION
Maximal contraction force can be produced with eccentric contraction, followed by isometric and then concentric.

PTHY 6401 Kinesiology I
LENGTH – TENSION RELATIONSHIP
 The force that a muscle can generate is dependent on the number of cross bridges that can be formed during contraction.
 This is dependent on the amount of overlap of actin & myosin in a muscle fiber.
 The amount of overlap is dependent on muscle length (ie. the position of the muscle as related to it's range of excursion).
 Example: the maximally lengthened position for the brachialis is full extension of the elbow & the maximally shortened position is full elbow flexion.
 The length at which a muscle can produce it maximal force or tension is called the optimal length. This is the length at which the actin & myosin can form the most cross bridge links. At lengths shorter or longer than the optimal length, a muscle cannot develop its maximal force when stimulated to contract.
DO NOT CONFUSE TENSION (force) WITH TORQUE
Active & Passive Insufficiency
 AI: is the decreased force production of a muscle when the muscle attachments are either too close OR too far apart (puts the sarcomeres in the ascending or descending parts of the lengthtension curve).
 PI: When a muscle is being STRETCHED (while it is relaxed), the
STRETCH results in tension being generated in the muscle. The tension may either create or limit joint motion
 Most common in two-joint muscles
Fig 3-5 in Neumann
Fig 3-11 in Neumann