Muscle blood Flow: Response to exercise

What happens to force production when muscle perfusion is reduced

O2 delivery to the muscle drops and force production is also reduced

What is the oxygen conforming response

the ability for the muscle cell to adjust oxygen consumption according to its availability

What happens is oxygen delivery is reduced

the muscle naturally lowers its ATP demand by reducing force output

How does the nervous system compensate if muscle oxygen drops but force production must be maintained

it will increase motor neuron activation otherwise ATP has to come from an anaerobic pathway which is less efficient

What does an increase of motor neuron activation lead to

it lead to a greater recruitment of muscle fibers and increased metabolite production

What was the objective of Study 1

evaluate what is the influence of changes in O2 concentration on intramuscular PCr and Pi at identical submax workload and if changes in O2 concentration lead to different exhaustion points of max work rates

What was the procedure of Study 1

participants performed incremental calf planter flexion exercises to exhaustion under 3 different inspired oxygen fractions conditions

What were the 3 different inspired oxygen fraction conditions

Normoxia = 21% (normal CaO2)
Hypoxia = 10% (reduced CaO2)
Hyperoxia = 100% (increased CaO2)

What was measured in Study 1

changes in muscle PCs and Pi through 21P-magnetic resonance spectroscopy

What does muscle oxygenation determine

it determines how much PCr and Pi must change to achieve any given muscle power output

What was the results of Study 1

Compared to normoxia, power output achieved and time to exhaustion was decreased with hypoxia and increased with hyperoxia; but exhaustion occurred at the same muscle metabolic state across conditions

Where was depletion of PCr more significant

it was more significant in hypoxia vs hyperemia

What condition produced more metabolites

hypoxia produced more metabolites to create the same intensity of exercise

For which condition did participants exhaust faster

they exhausted faster for hypoxia showing that metabolite concentration defines exhaustion

What was the objective of study 2

evaluate how changes in arterial oxygen content affect peripheral fatigue during intense exercise

how was test 1 performed for study 2

it was performed while breathing a hypoxic oxygen fraction of 15% until exhaustion

How were tests 2 and 3 performed for study 2

they were time matched with the hypoxic trial while the subjects breathed either a Normoxic oxygen fraction (21%) or hypoxic oxygen fraction (100%)

How was peripheral quadriceps fatigue assessed

it was assessed via changes in pre- vs post-exercise force output in response to supra-maximal magnetic femoral nerve stimulation

how was central motor drive assessed

it was assessed via EMG of the vastus lateralis

what was the principle of magnetic femoral nerve stimulation

a magnetic coil placed over the femoral nerve gave magnetic impulses to stimulate the nerve

what does the magnetic femoral nerve stimulation measure

it measures the force of the quadriceps triggered involuntarily

what was the purpose of magnetic femoral nerve stimulation

assess peripheral fatigue and test whether a voluntary contraction is truly maximal and asses nerve activity

What does EMG measure

it measure nerve activity and the electrical activity generated by muscle fibers when activated by nerves

what is the set up of EMG

surface electrodes or needles are placed on the muscle

what is the purpose of EMG

monitor level of muscle activation during a movement or effort and study changes in the signal during fatigue

What was the result of study 2 for the effects of CaO2 on peripheral locomotor fatigue

the reduction in quadriceps twitch force was significantly greater in hypoxia than in normoxia and greater in normoxia than in hyperoxia.

Changes in CaO2 during exercise at given power output affects the rate of peripheral locomotor muscle fatigue development

what was the results of study 2 for CaO2 on central motor drive

changes in CaO2 affect the amount of central motor drive required to achieve a given power output

what was the result of study 2 on the effects of CaO2 on exertional symptoms

Changes in CaO2 affect ratings of perceived muscle fatigue/effort

what is exercise induced fatigue

reduction in power and force from the contracting skeletal muscle which can effectively diminish performance

what does central/peripheral interaction depend on

it depends on exercise intensity and duration

what are the main factors of exercise induced fatigue

fitness level, nutritional status, intensity and duration of exercise, environment, sex, age, health status

What happens in the muscle when there is an increase in Pi levels

concentration gradient changes
Pi precipitated with Ca2+ causing less contraction
increase in H+ decrease pH

What happens to pyruvate during exercise

it can change into lactate which will bind to H+ to NADH and counteract an acidic environment

What are the main contributors to fatigue during moderate and prolonged exercise

increased of reactive oxygen species and decrease in glycogen

What happens when electrons leak out into the cytoplasm and bind to oxygen

creates O2- and H2O2 which can damage proteins, mainly ryanodine receptors which will leak out calcium from SR and decrease amount of calcium available to induce muscle contraction

What are the sites of central fatigue

brain, upper and lower motor neurons, neurotransmitter systems, and metabolite feedback

what happens when you sweat

there will be a loss in sodium which will alter ion balance and can impair action potential generation and propagation in neurons

What does prolonged exercise do to the neurotransmitter systems

it can disrupt neurotransmitter balance and excessive release and impaired reuptake reduce the ability to efficiently active motor neurons

What is perceived fatigue

feeling of fatigue or effort experienced by an individual influenced by psychological and external factors even when muscle performance is maintained

what is measurable fatigue

objective reduction in the muscles ability to produce force, power or sustain a given contraction

what are performance based tests for measurable fatigue

vertical jump test, sprint test, manual muscle test

what are methods of measuring measurable fatigue

surface electromyography, magnetic femoral nerve stimulation, force and power measurements

what are strategies to prevent or reduce fatigue

training periodization, nutritional strategies, warm-up/cool down routines, recovery methods