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chapter 4 book notes
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Ch 4 - Exercise Metabolism
- during exercise energy expenditure can increase 15-25 times above rest
Domains of Exercise Intensity
Intensity Lactate
threshold
% max HR %VO2 max Perception of
intensity
Moderate < 50-75 <60 Light to
somewhat hard
Heavy > 76-85 60-75 Hard
Very heavy > 86-100 76-100 Very hard
Severe 100 >100 All out, max
effort
Energy Requirements at Rest
- rest – almost 100% of energy is produced anaerobically
- low
Rest-to-Exercise Transitions
- takes 1-4 mins to reach steady state VO2 during submax exercise
- ATP-PC is the first active bioenergetic pathway, second is glycolysis, third is aerobic
energy production
- rest-work transitions use all 3 metabolic systems overlapping
- oxygen deficit – lag in O2 uptake at the beginning of exercise so most ATP is produced
anaerobically
odue to inadequate O2 delivery to the muscle or failure of oxidative
phosphorylation to increase immediately
- trained individuals reach steady state VO2 faster than untrained smaller O2 deficit
less lactate and H+ production
Recovery From Exercise
- O2 uptake is above the level needed to meet demands for several minutes post exercise
- post-exercise metabolic rate is influenced by the intensity of exercise
- EPOC (O2 debt) – excess post exercise oxygen consumption
orapid portion for 2-3 mins: O2 required to resynthesize stored ATP and PC &
replace O2 tissue stores
oslow portion for 30 mins following heavy/severe exercise: convert lactate to
glucose (gluconeogenesis), elevated HR and breathing, elevated body temp,
elevated hormones
- EPOC is greater after higher intensity exercise – but this does not significantly increase
weight loss
- most lactate is converted to pyruvate and then used in the heart and skeletal muscle
- lactate removal is more rapid with a cooldown than resting recovery
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Metabolic responses to exercise: influence of duration and intensity
short-term, severe exercise
- 2-20 sec: dominated by ATP-PC system
- more than 20 sec: relies more on anaerobic glycolysis
- more than 45 sec: combo of all, 50/50 aerobic/anaerobic
prolonged exercise
- mostly aerobic if more than 10 mins
- steady state O2 uptake can generally be maintained
- hot & humid or continuous & high intensity: drift upward of O2 uptake, steady state is
not maintained
Incremental exercise
- graded exercise tests
- test CV fitness
- maximal O2 uptake or VO2max – physiological ceiling for the ability of the O2 system to
deliver O2 to contracting muscles
- O2 uptake increases linearly until max is reached
- physiological factors that influence VO2 max: max ability of CR system to deliver O2 and
the muscles ability to take up the O2 to produce ATP
- genetics and exercise also influence VO2 max
lactate threshold
- point during graded exercise test when the blood lactate concentration increases
abruptly
- formation of lactate during exercise
omitochondrial hydrogen shuttle system fails to keep pace with the rate of
glycolytic production of NADH + H+ results in the conversion of pyruvate to
lactate
oinvolvement of more fast fibers may result in increased lactate production and
thus be responsible for the lactate threshold
oincrease in lactate production or decrease in lactate removal
- low muscle oxygen, accelerated glycolysis due to epinephrine, recruitment of fast-twitch
fibers & reduced rate of lactate removal lactate threshold
practical use of lactate threshold
- predict endurance performance and marker of training intensity
Estimation of Fuel Utilization during exercise
- ratio of volume of CO2 produced vs O2
- VCO2/VO2
- for R to be used as an estimate – subject must have reached steady state
oonly during steady state are the VCO2 and VO2 reflective of metabolic exchange
of gases in tissues
- the caloric equivalent for O2 is approximately 4.7kcal/L when fat is 5.0kcal/L
.7 = all fat
1.0 = all carbohydrate
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Factors Governing Fuel Selection
- whether fat or cabs are the primary substrate during work is determined by
odiet
ointensity and duration
owhether or not the subject is endurance trained
exercise intensity and fuel selection
- low intensity – fat
- higher intensity – carbohydrate
- R increases as exercise intensity increases
- switches from fats to carbs as intensity increases
- crossover point – where fat is less than carbohydrates
- what causes the shift from fat to carbs?
orecruitment of fast fibers
oincreasing blood levels of epinephrine
exercise duration and fuel selection
- fat metabolism only occurs after 10-20 mins, lipolysis is a slow process
- if you consume a high carb meal or drink 30-60min prior to exercise blood glucose inc
blood insulin inc lipolysis dec
interaction of fat/carb metabolism
- depletion of muscle and blood carbs results in muscular fatigue
- dec carb dec rate of glycolysis dec pyruvate in muscle & kreb cycle intermediates
dec aerobic ATP production
- dec kreb cycle intermediates results in reduced fat metabolism
- dec carbs = dec rate in fat metabolism
body fuel sources
- sources of carbs during exercise
oglycogen in muscle and liver
oblood glucose
- sources of fat during exercise
otriglycerides in adipocytes and muscle cells
oplasma FFA
- sources of protein during exercise – less than 2% of fuel source in less than 1hr; 5-10% in
3-5 hours
odegraded to AA
osupplied to muscle
- lactate as a fuel source during exercise
oserves as a substrate fro the liver to synthesize glucose anddirect fuel source for
skeletal muscle and heart
olactate shuttle: lactate produced in one tissue and then transported to another
for a fuel source
