exercise physiology chapter 4: exercise metabolism

resting energy expenditure: at rest, ATP is produced almost 100%

aerobically

oxygen consumption (VO2) provides an index of

aerobic ATP production (aerobic metabolsim)

avg VO2 at rest

70 kg person = 0.25 L/min VO2

3.5 ml/kg/min

1 MET

3.5 ml/kg/min

because oxygen is readily available at rest, pyruvate enters the Krebs cycle rather than being converted to lactate, so

blood lactate levels are low ( <1 mmol/L)

rest to exercise transition: at the onset of exercise, ATP demands

increases instantaneously

rest to exercise transition: at the onset of exercise, VO2

does not increase instantaneously

rest to exercise transition: at the onset of exercise, initial ATP production is through

anaerobic pathways

rest to exercise transition: overlap of what systems

ATP-PC, glycolysis, aerobic pathway

for light to moderate exercise, steady state VO2 occurs within

1-4 minutes

oxygen deficit

lag in VO2 at the onset of exercise

oxygen deficit provides information about the

regulation of oxidative phosphorylation

trained subjects have a _________ oxygen deficit

lower

why do trained subjects have a lower oxygen deficit

better developed aerobic bioenergetic capacity, cardiovascular or muscular adaptations, aerobic metabolism is active earlier ( and less lactic acid produced )

in the transition from rest to light or moderate exercise, oxygen uptake increases rapidly, generally reaching a _________ within 1 to 4 minutes

steady state

the term ________ applies to the lag in oxygen uptake at the beginning of exercise

O2 deficit

the failure of oxygen uptake to increase instantly at the beginning of exercise suggests that ________ pathways contribute to the overall production on ATP early in exercise. After a steady state is reached, the body’s ATP requirement is met via ________ metabolism.

anaerobic; aerobic

why does oxidative phosphorylation not achieve full activation instantaneously at exercise onset

inadequate oxygen supply to muscles at exercise onset or delay in stimuli (ADP and Pi concentrations) to fully activate oxidative phosphorylation

inadequate oxygen supply to muscles at exercise onset explained

mitochondria may not have enough oxygen molecules present and therefore available to participate in the ETC, thus restricting aerobic ATP production. this may hold true at very high intensity work.

oxygen debt

elevated VO2 (above resting levels) following exercise

“rapid” phase of O2 debt (2-3 minutes)

resynthesis of stored PC and restoration of muscle & blood O2 stores (on hemoglobin and myoglobin)

“slow” phase of O2 debt (>30 min)

elevated heart rate and breathing = increased energy needed

elevated body temperature = increased metabolic rate

elevated epinephrine and norepinephrine (catecholamines) = increased metabolic rate

conversion of lactic acid to glucose (gluconeogenesis)

term oxygen debt first used by

AV Hill

Hill believed that the elevated O2 consumption postexercise was repayment for

O2 deficit at onset of exercise

Current evidence shows that elevated O2 consumption post exercise

is not primarily due to repayment of “borrowed” O2

EPOC definition

excess post exercise oxygen consumption

EPOC coined to replace the term oxygen debt because

only about 20% elevated O2 consumption is used to repay O2 deficit (but often used interchangeably with oxygen debt)

factors responsible for rapid portion of EPOC

resynthesis of PC in the muscle, restoration of muscle and blood oxygen stores

factors contributing to EPOC

resynthesis of PC in the muscle, lactate conversion to glucose, restoration of muscle and blood oxygen stores, elevated body temperature, post exercise elevation of HR and breathing, elevated hormones

oxygen deficit and EPOC are

intensity dependent

Why is EPOC greater following high intensity exercise

higher body temperature

greater depletion of PC, additional O2 required for resynthesis

greater blood concentrations of lactic acid, additional O2 required for greater levels of gluconeogenesis

higher blood levels of epinephrine and norepinephrine

the ___________ (EPOC) formerly known as ____________ is the oxygen consumption above rest following exercise

excess post exercise oxygen consumption; oxygen debt

several factors contribute to EPOC. first, some of the O2 consumed early in the recovery period is used to resynthesize __________ in the muscle and replace ___________ in both muscle and blood. other factors that contribute to the “slow” portion of the EPOC inclide an elevated ___________ and ___________ and elevated ___________, O2 required to convert lactate to ___________, and elevated blood levels of ___________ and ___________

phosphocreatine; oxygen; body temp; breathing rate; heart rate; glucose; epinephrine; norepinephrine

bioenergetic pathways for short term, high intensity exercise: energy mostly comes from ___________ pathways

anaerobic

whether ATP provision comes from the ATP-PC system or glycolysis depends on the

length of the activity

first 1-15 sec of short term, high intensity exercise energy comes from

ATP-PC system

grater than 15 seconds, shift to energy for short term high intensity exercising coming from

glycolysis

greater than 45 seconds, shift to energy for short term high intensity exercise coming from

anaerobic and aerobic metabolism

at 60 seconds of short term high intensity exercise, energy is ______ anaerobic and ___________ aerobic

70%; 30%

at 2-3 minutes of short term high intensity exercise, energy is _______ anaerobic and ___________ aerobic

50%; 50%

during high intensity, short term exercise (i.e. 1 to 15 seconds), the muscles ATP production is dominated by the ___________

ATP PC system

intense exercise lasting more than 15 seconds relies on ___________ to produce much of the needed ATP

glycolysis

finally, high intensity events lasting longer than 45 seconds use a combination of the ___________, ___________, and ___________ to produce the needed ATP for muscular contraction, with a ___________%/___________% (anaerobic/aerobic) contribution needed for exercise lasting between 2 and 3 minutes

ATP-PC; glycolysis; oxidative phosphorylation; 50; 50

bioenergetic pathways for prolonged exercise: ATP production is primarily from

aerobic metabolism

prolonged exercise: steady state oxygen uptake can generally be maintained during

submaximal exercise

exceptions to state state being maintained during submaximal exercise (prolonged exercise)

moderate exercise intensity (50% VO2 max) in a hot and humid environment

high exercise intensity (>75% VO2 max) in a cool environment

what causes the drift in steady state maintenance?

elevated body temp/elevated epinephrine and norepinephrine

the energy to perfrom prolonged exercise (i.e. more than 10 minutes) comes primarily from ___________

aerobic metabolism

a ___________ oxygen uptake can generally be maintained during prolonged, moderate intensity exercise. however, exercise in a hot/humid environment or exercise at a high relative work rate results in an ___________ in oxygen consumption over time; therefore, a ___________ is not obtained in these types of exercise

steady state; upward drift; steady state

bioenergetic pathways for incremental exercise: VO2 max

maximal capacity to deliver and utilize oxygen during exercise; when an increase in workload no longer evokes an increase in O2 consumption

VO2 max is affected by

genetics and training

fick equation

VO2 = CO X (a-v O2 difference)

physiological factors affecting VO2 max

fick equation

maximum ability of cardiorespiratory system to deliver oxygen to the muscle

maximum ability of muscles to use oxygen and produce ATP aerobically

GXTs (graded exercise tests) are used to

assess cardiorespiratory fitness

blood lactate accumulation during incremental exercise: lactate production

skeletal muscle — fast twitch (produces lactate)

blood lactate accumulation during incremental exercise: lactate removal

liver, heart, muscle

most ATP comes from

aerobic sources during early incremental exercise (lower intensity)

as exercise gets harder (higher intensity) blood lactate concentration _______

increases

lactate threshold

work rate at which blood lactate rises systematically during incremental exercise

lactate threshold appears at _______ in untrained individuals

50-60% VO2 max

lactate threshold for trained subjects appears

65-80% VO2 max

lactate threshold aka

anaerobic threshold

“OBLA” (4mmol/L)

the lactate threshold represents

an increased reliance on glycolysis

possible explanations for lactate accumulation with increased exercise

low muscle oxygen (hypoxia)

accelerated glycolysis

recruitment of fast twitch fibers

reduced lactate removal

low muscle oxygen (hypoxia)

low levels of oxygen in individual muscle cells

accelerated glycolysis

increased epinephrine at 50-60% VO2 max stimulates glycolytic rate

H+ from NADH + H+ that is produced from glycolysis must be shuttled into the mitochondria

during intense exercise, shuttling is not fast enough, so NADH + H+ accumulates

to regenerate NAD to keep glycolysis going NADH + H+ donates its H+ ions to pyruvate and lactate is formed

recruitment of fast twitch fibers

slow twitch vs fast twitch muscle recruitment

type of LDH present in fast twitch fibers promotes the formation of lactic acid from pyruvic acid

reduced lactate removal

as exercise intensity increases, muscles receive a greater % of cardiac output

blood is shunted away from liver (as a site of lactate removal)

many faces of lactate

intracellular lactate shuttle and intercellular lactate shuttle

intracellular lactate shuttle

lactate is produced in the cytoplasm of a muscle fiber and can be taken up by the mitochondrion within the same fiber and used as fuel

intercellular lactate shuttle

some (25%) is used for gluconeogenesis in the liver

most (75%) is used in muscle aerobic metabolism

lactate in the blood travels to slow twitch myocytes and cardiac myocytes, where it is then converted back to pyruvate

classic theory of removing lactic acid following exercise

majority of lactic acid converted to glucose in liver

recent evidence of lactic acid removal following exercise

70% is oxidized and used as a substrate by heart and skeletal muscle

20% converted to glucose

10% converted to amino acids

lacid acid is removed more rapidly with

light exercise in recovery (optimal intensity 30-40% VO2 max)

does lactate cause muscle soreness

no

some athletes and coaches believe that lactic acid production during exercise is a primary cause of delayed onset muscle soreness that occurs 24 to 48 hours following an exercise session.

DOMS

delayed onset muscle soreness (24-48 hr)

why does lactate not cause DOMS

lactic acid removal from blood is rapid and levels return to normal within an hour following exercise

if lactate production caused muscle soreness, sprinters (track athletes that run 100 to 400 meter events) would experience soreness following every training session, but

muscle soreness is rare following routine workout

what causes DOMS

originates from microscopic injury to muscle fibers resulting in slow series of biochemical events leading to inflammation and swelling within the injured muscle

effect of training on lactate threshold: trained individuals can reach _______ before LT occurs

higher work rates

possible mechanisms of trained individuals having a higher LT

reduced catecholamine release at higher intensities

more mitochondria for aerobic ATP production

LT is a useful predictor of success in _______

distance running

LT can serve as a guideline to _______

prescribe exercise programs (marker of training intensity, selection of training HR based on LT)

training near (just below) lactate threshold is effective in _______

shifting lactate threshold to the right

oxygen uptake increases in a _______ fashion during incremental exercise until VO2 max is reached

linear

the point at which there is a sudden increase in blood lactate concentration during incremental (graded) exercise is termed the

lactic threshold

controversy exists over the mechanism to explain the sudden rise in blood lactic acid concentrations during incremental exercise. it is possible that any one or combination of the following factors might provide an explanation for the lactate threshold: (1) low muscle _______, (2) accelerated glycolysis due to _______ (3) recruitment of _______ muscle fibers, and (4) a reduced rate of _______

oxygen; epinephrine; fast twitch; reuptake/removal

the _______ has practical uses, such as performance prediction and as a marker of training intensity

lactate threshold

respiratory exchange rate (RER)

non invasive technique used to estimate contribution of carbohydrate and fat to energy metabolism during exercise

fat and carbohydrates differ in the amount of _______ used and the amount of _______ produced during _______

O2; CO2; oxidation

RER =

VCO2 / VO2

RER AKA

respiratory quotient (RQ or R)

fat (palmic acid) =

C16H32O2

RER of fat (palmic acid)

0.70

glucose =

C6H12O6

RER of glucose

1.00

for RER to be used as an estimate of substrate utilization during exercise _______

must be at steady state

during most types of submaximal exercise RER would be between

0.70 and 1.00

using RER to estimate fuel utilization assumes that

protein is not used as a fuel during exercise

R of 0.70 means _______ fat and _______ carbohydrates

100%; 0%