Muscle Blood Flow: Lecture 6&7 Flashcards
(39 cards)
Define The Oxygen-Conforming Response
Refers to the rapid adjustment of force production at a given motor neuron activation to match changes in muscle oxygenation
Describe the relation between perfusion and force production
When muscle perfusion is reduced(i.e. thus reducing muscle oxygenation), force production is also reduced
When must motor neuron activation absolutely increase?
During exercise where muscle oxygenation is reduced AND force production must be maintained, motor neuron activation must increase to compensate
–Equals need for greater recruitment and greater metabolite production!
To what expense does the increase of muscle activation happen, when PcellO2 is low?
At the expense of disturbances to muscle metabolic and contractile function (i.e., accumulation of metabolites leading to fatigue) as well as symptoms of muscular fatigue/discomfort.
Effects of muscle oxygenation (PcellO2) on muscle metabolism & contractile function
H+ (from lactic acid): Inhibits Ca2+binding to troponin = Fatigue
Pi: decrease in SR release of Ca2+; decrease in myofibrillar Ca2+ sensitivity; and inhibits cross-bridge formation = Fatigue
How can motor drive be increased to maintain muscle production? (voluntary ex)
-Self encouragement
-Outside encouragement
- Nerve stimulation (has to be outside stimulation???)
albeit at the expense of higher ratings of perceived exertion
What does ADP and Pi stimulate?
ADP and Pi stimulate glycolysis = increase lactic acid production
Simply Define Hypoxia, Normoxia, Hyperoxia
Hypoxia: Low oxygenation
Normoxia: Normal oxygenation
Hyperoxia: High oxygenation
Compare power output, time to exhaustion, PCr & Pi levels in normoxia, hypo/hyperoxia (Hogan et al)
Compared to normoxia
-power output achieved & time to exhaustion (i.e.,exercise performance) was DECREASED with hypoxia INCREASED with hyperoxia
-BUT exhaustion occurred at the same “muscle metabolic state” across FiO2 trials([PCr] and [Pi] levels were similar at end-exercise)
What will happen to [PCr] and
[Pi] and [ADP] when theres a decrease in PcellO2 but we need to maintain
V’O2 and power output
DECREASE of [PCr] and INCREASE of [Pi]&[ADP] to maintain V’O2 and power output
Which factors stimulate glycolysis and what reactions does it result in?
How does an Increase in [Pi] and [H+] affect contractile function?
INCREASED [Pi] and [H+] combine to DECREASE muscle force production and INCREASE the rate of development of skeletal muscle fatigue (performance limitation - i.e., inability of muscle to produce force required to perform a given activity).
Why/when do ratings of perceived exertion increase?
As the skeletal muscle(s) fatigue and muscle force generating capacity DECREASES, neural drive to the contracting muscle(s) must INCREASE (i.e., recruit more and larger motor units) to MAINTAIN any given power output à ratings of perceived exertion.
Define blood flow
The volume of blood travelling through a blood vessel, organ or entire body through time
BLOOD FLOW (BF): VOLUME/TIME
General effect of metabolites on blood flow during exercise
Metabolites cause VASODILATATION
What counteract is necessary when metabolites cause vasodilation in certain parts of the body during exercise?Why?
Vasoconstriction elsewhere or else high risks of fainting because of low BP while blood flow is still high
Name examples of metabolites
CO2
Lactic Acid (La+ + H+)
K+
ATPs
O2
Temperature
Define BF response
Dynamic response of O2 delivery to a step increase in exercise intensity
Feedforward VS Feedback mechanisms
Feedforward: mechanisms that happens to cause a chain of reaction
Feedback: loop
Name different phases of BF response profile
Rest
Phase 1 (0-20sec): Feedforward
Phase 2 (20-…sec): Feedback
Which phase of BF response profile is mechanically induced and why/how? Chemically induced?
Phase 1 is a feedforward mechanism mechanically induced by muscle pump which causes rapid vasodilation
Phase 2 is a feedback mechanism chemically induced by local metabolites (plateau observed)
How does the muscle pump increase MBF?
The muscle pump increases MBF by increasing the pressure gradient between the arteries and veins with each muscle contraction.
When is muscle pump ineffective?
Muscle Pump is ineffective when the exercising muscle is above heart level because the veins are already empty and, therefore, the arterial-venous pressure gradient cannot be increased.
What correlation does “Feedforward” vasodilation dilation have with tension development & motor unit recruitment?
It is in proportion to muscle activation (i.e., tension development & motor unit recruitment)
