topic 3: exercise metabolism 1 & 2 - exercise physiology

energy requirements at rest (rest)

when aerobic metabolism dominates since O2 delivery is sufficient at a low energy demand

• uses VO2 (oxygen consumption) as a marker: the amount of oxygen consumed by the cells for ATP production

• more O2 = more aerobic metabolism = more utilized to make ATP for exercising muscles and other basic cellular functions

• ml/kg/min

• resting oxygen consumption = 3.5 ml/kg/min or 1 MET

energy requirements from rest to exercise (rest to exercise)

transition where ATP demand increases immediately, and ATP comes mainly from ATP-Pc and glycolysis (anaerobic metabolism)

• oxygen deficit

• steady state

• delay/lag

oxygen deficit

period from rest to exercise where there is a temporary shortfall in oxygen supply

• relies on anaerobic energy systems to supply ATP

• ATP demand jumps up, but VO2 rises slowly but far from the line of demand

• ATP-Pc: stored ATP and PCr (0-10 sec of exercise)

• glycolysis: breakdown of glucose to lactate and make ATP (10 sec-2 min of exercise)

steady state

period from rest to exercise where the amount of oxygen consumed meets the demand in generating ATP

• can start oxygen consumption

• when VO2 meets the demand

• around 3-4 min

• aerobic metabolism can dominate again

delay

period from rest to exercise when there is not enough oxygen to meet the demands of aerobic metabolism

• muscles contract immediately, and ATP demand increases instantly

• it takes a long time for O2 to travel through respiratory and cardiovascular systems

• to compensate, the body temporarily uses anaerobic systems until enough O2 is present

• oxygen consumption (VO2) starts low then rises gradually as HR, breathing, blood flow, etc increase

trained vs untrained oxygen deficit

trained individuals: reach steady state faster and have a smaller oxygen deficit

• more training improves CV and cellular function

• consume O2 more efficiently and faster because of speedy O2 delivery and aerobic metabolism

energy requirements for recovery (recovery)

metabolic responses after exercise when the body still needs ATP to restore the body to resting conditions

• excess post-exercise oxygen consumption (EPOC): submaximal exercise

excess post-exercise oxygen consumption (EPOC)

the elevated oxygen consumption after exercise used to restore systems to resting levels

• increases with exercise intensity

• submaximal (?)

• O2 consumption can decrease about 50% for every 30 sec after exercise, so doesn't completely drop to 0 after stopping exercise

• need O2 to keep heart muscles pumping

EPOC factors

of oxygen debt

• resynthesis of PC in muscle

• lactate conversion to glucose:

  • lactate was oxidized aerobically and used as a fuel source (70%) for ATP

  • small portion of lactate converted in the liver thru gluconeogenesis

• restoration of muscle and blood oxygen stores

• elevated body temp

  • Q10 effect: hot body = consume more O2 to fuel rates

• post-exercise HR and breathing elevation

• elevated hormones

  • epinephrine and norepinephrine

EPOC at moderate vs heavy exercise (EPOC moderate vs heavy)

moderate: EPOC recovery is lower and shorter since the body’s aerobic metabolism can largely meet demands

heavy: EPOC recovery is greater because of a larger oxygen deficit

• heavy exercise depletes PCr

• more anaerobic metabolism = more lactate = requires more O2 for recovery

• higher body temp, HR, breathing, hormones

maximizing recovery

after heavy exercise, the goal is to return systems to resting levels as quickly as possible

• passive recovery: complete rest, slower lactate clearance

• active recovery (more efficient): using low-intensity exercise/activity to increase blood flow and O2 delivery for aerobic metabolism removal of lactate

  • ex: light cycling, jogging

short term intense exercise

metabolic responses uses ATP supplied by anaerobic systems

• ATP-Pc: 0-10 sec

• glycolysis: peaks at 1 min

• steady state of oxygen consumption is reached more quickly and can usually be maintained

• ex: 100m sprint

prolonged exercise

metabolic response uses ATP supplied by aerobic systems for longer than 10 min

• higher power = higher O2 uptake

• higher work rate = >75% VO2 max and cannot sustain steady state even at constant workload

• steady state cannot be sustained b/c of lactate accumulation higher than threshold, increased type II fibers

• drift: gradual increase in HR and VO2 at constant workload in high-intensity hot/humid conditions

• ex: swimming laps, distance running, steady-pace cycling

incremental exercise

metabolic responses when increasing the workload (Watts)

• commonly VO2max to administer exercise tests and determine a subject’s maximal physiological ceiling

• VO2max: plateau on a work rate by VO2 graph (gold standard)

  • linear relationship where all body systems are MAXED out

  • O2 consumption increases VO2 over rise in difficult intensities

• bruce protocol: stages of increasing speed and percent grade

  • 3 min stages, measure HR, O2 consuming, CO2 expiring, bp, expiring exertion, ECG strip

  • until the subject cannot go anymore

• lactate threshold

• active: 80+ ml/kg/min VO2

• diseased: 5-10 ml/kg/min VO2

verifying VO2max

• plateau (gold standard) on work rate by VO2 graph

  • no longer increases despite increase in workload

  • not everyone shows a clear one

• APHRMax: age predicted HR max — need another variable since lots can affect HR

• lactate ≥ 8 mM: elevated lactate levels can indicate VO2 max at near maximal intensity since anaerobic metabolism

• > RER1.15: respiratory exchange ratio — suggests maximal effort, O2 consuming vs CO2 releasing due to burning carbs as a fuel source = anaerobic

trained vs untrained VO2max

trained person: significantly higher VO2max than untrained person

• have a trained CV, muscular, and metabolic systems that are stronger and take in O2 to the muscles quicker

• more mitochondria

lactate threshold

as intensity and percent VO2max increases, it is the point where lactate production increases faster than it is cleared

• marks a rapid rise in blood lactate

• reflects a shift toward greater anaerobic metabolism

• around 60% VO2max but higher in trained individuals

• is below VO2max but about to reach physiological ceiling

• occurs at lower intensity than VO2max = good for exercise programs to define the highest sustainable workload

• clearance of blood also occurs by the liver – to generate fuel source

• OBLA (onset blood lactate accumulation): what the lactate level is at any particular exercise intensity

lactate mechanisms

producing more lactate at high intensity exercise because we are in anaerobic metabolism

1) low muscle O2: subject unable to bring in enough O2, so switch to anaerobic

2) accelerated glycolysis: more carbs as primary fuel source vs fats/proteins

3) recruitment of fast-twitched fibers: during high intensity exercise, quick in duration

• holds more lactate dehydrogenase (pyruvate → lactate)

4) reduced rate of lactate removal: lactate needs O2 to be used as an efficient fuel source

soreness

lactate does not cause muscle soreness and is likely due to microtears in muscle fibers throughout a few days

• lactate is a FUEL source, converted to glucose in the liver

• increasing exercise intensity increases acidic environment (drop in pH)

• H+ released during ATP hydrolysis: breakdown of ATP used by exercising muscle

• H+ accumulation makes you sore

training on lactate threshold

marker of training intensity:

• the highest you can sustain without rapid fatigue

• better marker for endurance than VO2max

choose a training HR based on LT

• HR at LT is measured/estimated

• below LT (easy, aerobic), at LT (tempo, threshold), above LT (interval)

• individualized

high volume, maximal steady state, and interval workouts

• high volume: low intensity work below LT to improve LT over time

• maximal steady state: continuous exercise at/near LT, sustaining high intensities, shift LT to higher % of VO2max

• interval training: short bouts above LT with recovery, improve tolerance to lactate, raises both LT and VO2max

respiratory exchange ratio (RER)

R = VCO2 / VO2

• V = coefficients in balanced equation

• uses a metabolic machine and analyzer to measure O2 used and CO2 produced

fat as fuel: more O2 to produce CO2 = 0.70

• take in O2 → breaks down fat to make acetyl-CoA → krebs cycle → ETC

• 23 O2 needed to break down to acetyl-CoA

• higher denominator = smaller number

CHO as fuel: less O2 to produce CO2 = 1.00

• 6 O2 needed to breakdown glucose

diet

factor governing fuel selection

• high fat (low CHO diet) → increases fat metabolism

• high CHO diet → increase glycogen utilization

intensity

factor governing fuel selection

• low intensity = fat metabolism

• high intensity = CHO metabolism

• moderate intensity: less reliance on fat and greater reliance on carbs

crossover concept

as intensity increases, more CHO is used

1) plasma FFA decreases, more muscle glycogen use increases (already stored)

• cannot maintain high intensity without glycogen and glucose

• fat cant meet ATP demand

• ex: 100 yd sprint — would want a high CHO diet

2) recruiting fast muscle fibers

• have more enzymes for glycolysis and anaerobic metabolism

3) increasing circulating epinephrine

• epinephrine is released at high intensity exercise or at the crossover → stimulates and increases cyclic AMP → activates pathways to make glycogen phosphorylase → glycogenolysis)

4) increasing lactate formation

• undergoing anaerobic metabolism converts pyruvate to lactate

• lactate INHIBITS triglyceride metabolism