Lecture 11 & 12 Energy Expenditure Flashcards
how do we measure energy expenditure
the energy used by contracting muscle fibres cannot be directly measured, but we have different lab methods we use to calculate whole body energy expenditure at rest and during exercise called
- > direct calorimetry
- > indirect calorimetry
how do we measure energy expenditure during direct calorimetry
- > we measure the body’s heat production as on 40% of substrates are used for ATP, the other 60% is converted into heat
- > we measure this with a calorimeter
how do calorimeters work
a person is in a chamber that is insulated with water, as the person in the chamber exercises, their body heat radiates out and into the water in the walls
- > your body temp increases the water and air temp
- > we can use that heat change to calculate your metabolism
pros and cons of calorimeters
Pros
- > accurate over time
- > good for resting metabolic measurements
Cons
- > hard to build room, requires engineering
- > expensive
- > slow
- > exercise equipment adds heat to room
- > sweat will create errors
- > not practical or accurate for exercise
how do we measure energy expenditure using indirect calorimetry
energy expenditure is determined by the rate of O2 usage and CO2 production in the lungs (looks at gas concentration)
- > this technique is limited to steady-state aerobic activities and metabolism must be oxidative and not anaerobic
what are the most accurate ways to determine gas concentrations in the lungs/body
- > older, more simpler methods are more accurate but take longer to perform (i.e. Douglas bag)
- > modern electronic computer systems for respiratory gas exchange measurements offer the ability to make rapid and repeated measurements
VO2 and VCO2
used in indirect calorimetry
VO2
- > volume of O2 consumed per min
VCO2
- > vol of CO2 produced
V(dot)O2 and V(dot)CO2
- > the rot above the v is the rate of Oxygen consumption or CO2 production per minute
possible variations in VO2/VCO2
the body stores some O2 in the body
general characteristics of VO2 and VCO2 measurements
- > able to produce an accurate reading for every breath inhaled or exhaled
- > average cost is lower and less time consuming than other methods
- > can be designed to be sports specific
respiratory exchange ratio (RER)
the ratio between the rate of CO2 release (VdotCO2) and O2 consumption (VdotO2)
- > the amount of carbon and oxygen in glucose, fat and protein differs dramatically, as a result, the amount of O2 used during metabolism depends on the type of fuel being oxidized
RER for 1 molecule of glucose
1.0
6O2 +C6H12O6 = 6CO2 +6H2O + 32 ATP
RER = VdotCO2/VdotO2
limitations to indirect calorimetry
*still provides the best estimate of energy expenditure*
- > CO2 production may not = CO2 exhalation
- > RER is inaccurate for protein oxidation
- > RER near 1 may be inaccurate with lactate buildup, as this causes increased CO2 production and its release
- > the breakdown of AA and fats (gluconeogenesis) produces an RER of >0.7
what is an isotope
elements with an atypical atomic weight
- > can be radioactive (radioisotopic) or non-radioactive (stable isotopes)
- > i.e. C^14 has a molecular weight of 14
deuterism
common isotopes used for studying energy metabolism
- > doubly labelled water = a known amount of water with 2 isotopes (2^H2 and 18^O)
- > the deuterism (H) diffuses through the body’s water and O2 diffuses through water and bicarbonate stores
- > the rate of which that these two isotopes leave the body can be used to determine how much CO2 is produced
- > easy, accurate, low risk study of CO2 production, ideal for long term measurements (weeks)
metabolic rate
the rate of energy used by the body
energy expenditure at rest
*based on whole body O2 consumption and corresponding caloric equivalent*
At rest
- > RER= 0.80 (0.3L/kg/min is standard measurement)
- > at rest, metabolic rate ~ 2000 kcal/day
Basal metabolic rate (BMR)
rate of energy expenditure at rest in a supine position (face up)
- > measured in a thermoneutral environment after 8hrs of sleep and 12 hrs fasting
- > represents the minimum amount of energy required to carry on essential physiological functions
- > can be affected by body surface area, age, stress, hormoones, body temp
BMR is directly related to _____
because muscle has high metabolic activity, BMR is directly related to an individuals fat-free mass
- > is reported in kcalxkgFFm^-1 x min^-1)
Resting metabolic rate (RMR)
- > similar to BMR, 5-10% difference from each other
- > 1200-1400 kcal/day
- > doesn’t require stringent standardized conditions
total daily metabolism (including normal daily activities)
1800-3000 kcal/day
- > competetive athlete up to 10000 kcal/day
metabolic rate during submaximal exercise
- metabolic rate increases with exercise intensity*
- > (slow component of O2 uptake) it takes about 2 mins after exercise start for body to bring amount of O2 needed to complete the task
- > at high power outputs, VO2 continues to increase
- > more type 2 (less efficient) fibre recruitment
- > at higher intensity exercise, the steady state rate takes more time to be reached (this is essentially the slow component of O2 uptake)
VdotO2 drift
a slow increase in VdotO2 during prolonged, submaximal, constant power output exercise
- > possibly due to hormone changes or ventilation
VO2 max
maximal capacity for aerobic exercise
- > point at which O2 consumption does not increase with further increase in intensity
- > highest amount of oxygen consumption, inhalation, transportation and ability to use it
- > best single measure of aerobic fitness/cardiorespiratory endurance
why is VO2 max not the best predictor of endurance performance capacity after 8-12 weeks of training
- > research shows that athletes will plateau after this time, despite continued higher intensity training
- > plateau only occurs if the increase in O2 matches the increase speed/intensity
- > performance will still improve
- > more training allows for athletes to compete at higher % of Vo2 max
VO2 max is expressed in which ways
it is typically expressed relative to body eight
- > ml x kg^-1 x min^-1
- > more accurate comparison for different body sizes
in non weight bearing activities (i.e. swiming)
- > endurance is reflected in L/min
VO2 max ranges for untrained young men and women
Men
44-50
Women
38-42
- > sex differences are different due to women’s lower fat-free mass and lower hemoglobin (O2 carrying capacity)
can activity be 100% anaerobic or aerobic, why?
NO
estimates of anaerobic effort involve…
- > excess post-exercise O2 consumption
- > lactate threshold
post exercise O2 consumption
O2 demand > O2 consumed in early exercise
- > body will develop an O2 deficit
- > calculated by (O2 required - O2 consumed)
- > occurs when anaerobic pathways are used for ATP production
O2 consumed > O2 demanded in early recovery
- > excess post-exercise O2 consumption (EPOC)
- > replenish ATP/PCr stores, converts lactate to glycogen, replenish hemo/myoglobin, resp remains elevated to clear accumulated CO2
lactate threshold
the point at which blood lactate begins to substantially accumulate
lactate production > lactate clearance rate
- > interaction of aerobic and anaerobic systems
- > good indicator of potential for endurance exercise
characteristics of lactate threshold
- > usually expressed as a % of VO2 mac
- > higher lactate threshold means better endurance performance
*for 2 athletes with the same VO2 max, the one with higher lactate threshold will perform better
as an athlete become more skilled ______
the energy demands during exercise at a given pace are reduced. body becomes more economical (economy of effort)
- > this is independent of VO2 max
Multifactorial phenomenon of the economy of effort
- > economy of effort increases with distance of race
- > practice=better economy of movement (form)
- > varies with type of exercise (running vs swimming)
characteristics of a successful athlete in aerobic endurance events
- > high VO2 max
- > high lactate threshold
- > high economy of effort
- > high % of type 1 muscle fibres (only provides a limited amount of endurance capacity
define fatigue
- > decrements in muscular perfomance with continued effort, accompanied by sensations of tiredness (exercise phys)
- > inability to maintain required power output to continue muscular work at given intensity (research studies)
how is fatigue reversed
it is reversed by rest
4 major causes of fatigue
- > inadequate energy delivery, metabolism
- > accumulation of metabolic by-products
- > failure of muscle contractile mechanism
- > altered neural control of muscle contractor
what happens during PCr depletion
fatigue coincides with PCr depletion
- > since PCr is used for short-term, high intensity effort, PCr depletion means that the ability to quickly replace spent ATP is hindered, leading to the accumulation of Pi
how do athletes ensure that PCr and ATP are not prematurely exhausted
they need to pace themselves
glycogen depletion
large correlation to glycogen depletion and fatigue during prolonged exercise
- > muscle glycogen is used/depleted more rapidly during the first few minutes of exercise vs the later stages; as well as with high intensity
glycogen depletion in different fibre types
muscle fibres are recruited and deplete their energy reserves in a specific pattern
- > fibres recruited first or most frequently deplete faster
- > type 1 fibres are depleted after moderate endurance exercise
muscle fibre recruitment order (consider glycogen depletion)
recruitment depends on exercise intensity
- > Type 1 are recruited first
- > type 2a are recruited next
- > type 2x are recruited last
depletion in different muscle groups
activity specified muscles deplete faster
recruited earliest and longest for given tasks
list the metabolic byproducts and how they contribute to fatigue
Pi
- > from rapid breakdown of PCr and ATP
Heat
- > retained by body, core temp increase
Lactic acid
- > product of anaerobic glycolysis
Lactate
how does heat and muscle temperature alter metabolic rate
heat/exercise…
- > increases rate of carb utilization
- > hastens glycogen depletion
- > high muscle temp may impair muscle function
relate to time to fatigue, to changes in ambient temperature
time to exhaustion is the longest in 11C
time to exhaustion is shortest at 31C
- > muscle pre-cooling prolongs exercise
when does lactic acid accumulate and why is this bad
it accumulates during brief high intensity exercise
- > if not cleared out immediately, it converts to lactate + H
- > H accumulation causes decreased muscle pH (acidosis)
how do buffers help with muscle pH
buffers minimize the disruptive influence of H ions that accumulate in the muscle
- > without theses buffers, H would lower the pH
ph< 6.9 inhibits glycolytic enzymes and ATP synthesis
pH = 6.4, the influence of H prevents further glycogen breakdown
resting pH = 7.1
relate neural transmission to fatigue
fatigue may occur at the neuromuscular junction, preventing nerve impulse transmission to the muscle fibre membrane
possible causes…
- > altered ACh breakdown in synapse
- > increase in muscle fibre stimulus threshold
- fatigue may inhibit Ca release from SR*
central governor theory
the CGT proposes that processes occur in the brain (CNS) that regulate power output by the muscles to maintain homeostasis and prevent unsafe measure of exertion that nay damage muscles or tissues
- > subconscious or unconscious unwillingness to endure more pain
- > discomfort of fatigue = a warning sign
