Exercise Phys: Muscle, Fuels, & Fatigue Flashcards
How is percent body fat related to % type I muscle fibres?
more type I fibres = less body fat (more oxidative, tf burn fat)
How are mitochondria related to insulin sensitivity?
more mitochondria = more insulin sensitive; greater disposal rate of glucose in response to insulin
Acid pre-incubation staining for myosin-ATPase shows
Dark type I fibres; light type II fibres (because fast-twich fibres are acid-sensitive)
Alkaline pre-incubation staining for myosin-ATPase shows
Light type I fibres; dark type II fibres
Type I fibres
Slow oxidative, slow-twitch
Type IIa fibres
Fast oxidative glycolytic; fast-twitch
Type IIx fibres
Fast glycolitic; fatigable fast-twitch
Time to peak tension (ms)
I > IIa > IIx
Force/power output
IIx > IIa > I
Endurance capacity
I > IIa > IIx
Distribution in whole muscle
I > IIa > IIb
Mitochondrial density
I > IIa > IIb
Capillary density (cap/fibre)
I > IIa > IIb
Fibre area (um^2)
IIa > IIx > I
What is the order of fibre type recruitment?
ST, IIa, IIb at highest threshold; at maximum exercise all fibre types are activated to maximize force
% ST:FT in untrained
~50:50
T/F Type IIa fibres can be trained to be more oxidative (type I-like) even though their contractile properties remain fast
T
T/F ST fibres are easily trained to FT fibres
False; easier to train FT to become ST
Early and rapid increase in strength in response to strength training is attributable to
neuromuscluar adaptation - recruiting more muscle to generate more force
Muscle disuse leads to rapid loss of
protein and CSA
What is the muscle atrophy pathway?
Foxo (transcription factor) is normally inhibited by Akt pathway (mTOR, muscle growth) but is activated in bed rest leading to protein degradation and muscle atrophy
Increased muscle mass is stimulated via which pathways?
(GH) and IGF-1 acting via Pi3K insulin pathway to activate Akt (inh Foxo and tf atrophy) and mTOR; glucocorticoids also act via Akt
What are the mitochondrial adaptations in muscle in response to exercise training?
increased mitochondrial density and oxidative enzymes; reduced CHO use and lactate production; increased fat oxidation; enhanced endurance performance; improved insulin action
Blood lactate levels serve as a biomarker of
mitochondrial density
T/F ATP drives muscle contraction
True; myosin ATPase, Na/K-ATPase, Ca-ATPase (SERCA)
T/F We have significant stores of ATP in muscle
False; in exercise it must be regenerated via substrate level or oxidative phosphorlyation
Substrate-level phosphorylation involves
energy released from metabolic pathways and CP is transferred to rephosphorylate ADP to ATP
Oxidative phosphorylation involves
e- reducing agents generated in TCA (NADH, FADH2) enter the ETC and regenerate ATP
What happens to the rate of ATP generation as you move from CP and glycolysis (substrate-level) to CHO and fat oxidation (ox-phos)?
Rate of ATP generation decreases
‘Hitting the wall’ refers to
being unable to maintain speed during endurance events because CHO stores are exhausted and metabolism is switching to fat oxidation - must slow down to maintain PO
CP and glycolysis have _____ power and ________ capacity
high; low
CHO and fat oxidation have _____ power and _____ capacity
low; high (depending on CHO reserves and diet)
T/F Endurance athletes do not have enough body fat to sustain exercise
False; even the skinniest endurance athlete has more than enough fat to keep them going for many days
What is the primary fuel in sprinting type activities?
anaerobic: ATP, PCr, glycolysis (glycogen –> lactate)
What are the relative contributions of Pcr, ATP, and glycolysis in sprinting?
highest contribution by PCr initially which decreases over 10-30s; ATP smallest contributor and also decreases over time; glycolysis significant from 10s-30s
What is the primary fuel in endurance exercise?
primarily aerobic (CHO and fat oxidation); 50% of 1 minute, 90% at 2 minutes; almost exclusively aerobic after 2 minutes
Exercise becomes almost exclusively aerobic beyond
2 minutes
T/F Protein cannot be used as a fuel in endurance exercise
False; muscle protein can be mobilized as fuel eg cyclist upper bodies
Protein contributes ____ to total energy expenditure in endurance exercise in a well-fed individual
<5% once CHO is depleted
The main fuels of aerobic metabolism are
CHO and fat
As exercise intensity and energy expenditure increases, what happens with regards to CHO?
increased reliance on CHO (muscle glycogen)
T/F At lower intensities, fat is making a major contribution as fuel
True; fat oxidation goes up at lower intensities, then goes down as intensity increases
What is the ‘fat max’?
the intensity of exercise where you get maximal fat oxidation
What are the relative contributions of muscle fats, plasma FFA, plasma glucose, and muscle glycogen during increasing intensity endurance exercise?
at rest predominantly plasma FFA and plasma glucose; muscle and plasma FFA use higher at lower intensities then decreases with increasing intensity; plasma glucose and muscle glycogen contributions increase with increasing intensity; muscle glycogen is the predominant fuel source at high intensity
What is the predominant fuel at high intensity endurance exercise?
Muscle glycogen
Over extensive time eg 4hrs endurance 65% VO2 max, what happens to reliance on CHO?
Reliance on CHO decreases as reliance on fat increases
Endurance exercise ceases when
rate of CHO oxidation is insufficient to support exercise intensity - decreasing intensity then prolongs endurance exercise
Ultra-distance runners typically operate at what %VO2 max?
50-60%
What factors influence exercise metabolism and fuel selection?
exercise intensity and duration; diet; training; environmental temp; age; sex
How does diet influence exercise metabolism?
high-CHO diet burns more CHO, high-fat burns more fat but intensity is limited
How does training influence exercise metabolism?
training adaptations in muscle lead to reduced reliance on CHO as fuel - can go to a higher intensity on the same amt of CHO
How does environmental temperature influence exercise metabolism?
exercise in heat = burn more CHO
How does age influence exercise metabolism?
bc VO2 max declines with age, exercising at the same intensity is a higher relative intensity, tf burn more CHO
How does sex influence exercise metabolism?
females use more fat than males, thought to be that oestrogen promotes fat oxidation
Influences on exercise metabolism are mediated by
substrate availability, hormone levels (insulin, glucagon, catecholamines, GH, cortisol) and characteristics of skeletal muscle - with training, mitochondrial content increases and this alters substrate selection
What is fatigue?
A reversible process which is induced by exercise and alleviated and reversed by rest - something has happened to change the characteristics of the muscle eg decrease in maximal force-generating capacity with prolonged exercise; Inability to maintain the required or expected force or PO - task-specific definition eg not being able to keep up with a competitor who is running at a faster pace
What is muscle weakness?
Chronic reduction in force-generating capacity of the muscle
Muscle weakness at rest indicates
problem with the muscle or NM system
Muscle weakness induced by exercise eg premature fatigue indicates
CV (eg IHD) or metabolic defects
What factors contribute to fatigue?
CNS central motor drive; muscle feedback - decreased ATP, increased H+ and ROS; lactic acid levels
Removing muscle feedback to the brain eg fentanyl causes
increased exercise intensity and duration - brain is not getting feedback that would normally cause it to cease the muscle activity
Blood lactate levels indicate
metabolic stress
How is glycogen related to fatigue?
glycogen decreases more rapidly with increasing intensity in type I fibres; IMP (breakdown product of ADP) accumulates as glycogen declines; fatigue is thought to be an imbalance of ADP formation and ADP re-phos to ATP - running out of glycogen, can’t maintain ATP tf have to slow down
T/F CHO ingestion prevents fatigue
False; ingestion (loading, CHO drinks during) can delay fatigue but does not prevent it
How do you increase fatigue resistance?
training (physical, technical, mental); optimize nutrition (CHO, fluids, protein); heat acclimatization and cooling; drugs, supplements, gene doping eg PPARdelta to increase oxidative capacity
