Tension
Force developed when contracting acts on object
Load
Force extended on muscle
*Load and muscle tension are opposing forces
Torque
-The capacity of force or tension to produce rotation of limb around a joint
Isotonic Contraction
- tension generated by muscle fiber is constant through ROM
*Refers to the Muscle fiber
-in the intact human system such a contraction is practically impossible
Dynamic contraction
*refers to the whole muscle
-force exerted varies as muscle shorten to accommodate change in length and or joint angle through ROM
can be concentric (shortening) or eccentric (lengthening),
-eccentric causes the most soreness
Isokinetic Contraction
-muscle fiber contraction where velocity of contraction is kept constant
Isokinematic Contraction
-whole muscle rate of limb displacement or joint rotation held constant with use of specialized equipment
Isometric contraction
-muscle fiber contraction that does not result in a length change in the muscle fiber
Static Contraction
-whole muscle contraction which increase tension with no meaning movement of skeleton
Type of work
Positive work mean its against gravity
Negative work means its with gravity
Static and isometric have zero work because you move no distance
(work= force x distance)
Force development of contractions
-the amount of force generated is not the same for all contractions
-eccentric dynamic contraction = most force
static contraction = middle
concentric dynamic contraction = least force (most of your daily activities)
Tonus contractions
contractions that are static in nature (what we do when we eat stand and sleep)
-there is no meaningful movement (or we would all be jerking around) but they contract to help you stand up right
Gradation of Response for a single muscle fiber
a single muscle fiber will contract maximally or not at all
-this is the all or nothing principle (but does not apply for whole muscle contractions)
Gradation Response of whole muscles
-does not follow the all or nothing principles
-whole muscle contraction is called tetanic contraction
-tetanic contraction can be graded (which means muscle contraction can produce a little force or a lot of force)
Neural factors that determine force production in whole muscles
1) rate-coding
-the frequency of stimulation
-as the frequency increases the force increases
2)recruitment
-you can vary the number of motor units recruited
-this is a conscious learned response that becomes unconscious
Graphs describing contraction, tone
-contraction is faster then relaxation period in skeletal muscle
-muscle tonus is maintained by some motor units always contracting in an alternating manner in the intact human
4 Mechanical factors that influence the force produced during muscle contraction
1) length-tension relationship
2) force-velocity relationship
3) the elasticity-force relationship
4) the cross-sectional area design
Length-tension relationship
-within a muscle fiber the amount of tension that can be exerted is related to the initial length of the sarcomeres
-an elongated fiber has to littler overlap of actin and myosin making it hard for cross-bridges to form
-a shortened fiber where then thin
Force-velocity Relationship
-a muscle shortens slowest when the load is the heaviest
-a muscle shortens fastest when the load is the lightest
-this relationship is the same for the whole muscle and a single muscle fiber
-as you increase velocity the force generated is low and vis. v
Looking at the mechanical factors of max velocity
-at the cell level, max velocity of shortening is constant regardless of sarcomere length
-length of sarcomere influences force production but not velocity
-max velocity of shortening does not depend of number of cross-bridges but on max cycling which is
Power-velocity relationship
1) power is positively related to velocity
2) the relationship is curvilinear
3)The power that can be generated at any give velocity depends on muscle fiber type
This mean muscles with predominately FT fibers can produce more power then muscles with predo
Elasticity-force relationship
-when a muscle fiber is stretched an then contracted the resulting contraction is stronger then without pre-stretching
-the stretch shoring cycle leads to more power muscle contraction an effects mechanical efficiency
-think jumping without bending you le
Cross-Sectional Area/ Architectural design
Lower velocity of shorting designs=High force are:
-pennate, bipennate, multipennate
this is because they maximize cross-sectional area
High velocity of shorting designs = less force are:
-Fusiform, longitudinal and parallel fibers
Muscular Fatigue
-appears to be caused by failure at one or more of the sites along the chain of events that leads to muscular contraction
-can be classified as central or peripheral based on the site of fatigue
-central refers to the nervous system(brain, spinal chord)
-
Central Fatigue
-can be related to neurons in the brain or spinal chord
-inhibitory input from the muscles afferent innervating neurons in the brain or alterations in motor neurons
-also can by influenced by psychological factors such as motivation
Peripheral Fatigue
-can occur an where from the neuromuscular junction to the skeletal muscle
-can occur as the neuromuscular junction, the sarcolemma, T Tubules, Sarcoplasmic reticulum and the myofilaments
-can ale be caused by problems with binding or depletion of neurotr
Electrophysiological and contractile-biochemcial considerations of muscle fatigue
-electrophysiological refers to any steps involved with the CNS, peripheral nervous system or muscle fiber leading up to the binding of actin myosin filaments
-contractile consideration involve the ability of actin and myosin to continue their cross-bridg
Muscle Soreness (DOMS= delayed onset muscle soreness)
-muscle tenderness
-pain on palpitation
-mechanical stiffness 8 hours after exercise
-increases and peaks over 24-48 hours
usually subsides with in 96 hours
Model for delayed soreness
1) unaccustomed high force activity causes a disruption of structural proteins in the muscle fiber
2)damage to the sarcomere cytoskelton inhibits ATP production which causes intracellular calcium to increase
3) high calcium concentration leads to degradat
Why is it important to measure muscle balance
1) determine weakness or imbalance which can make a person more prone to injury
2) necessary to guide rehab
3) necessary for exercise prescription
4) selection of the best exercise for working specific problems
5) research tool for understanding which tra
Laboratory methods
-EMG
measure electrical activity and motor unit recruitment
-Isokinetic machines
provide accurate and reliable measurements of muscular strength, muscular endurance and power while the peek of the limb is kept constant
-Force Transducer
measures static st
Field tests
calisthenics aka sit-ups, push-ups and flexed arm hang