Ex PHYS Exam #2

ATP

40% of substrate energy (substrate metabolism efficiency)

heat

60% of substrate energy (substrate metabolism efficiency)

increases ↑

Heat production _____ with energy production

Heat production ↑ with energy production

* Measurement of energy expenditure
* The “calorie” is the basic unit of heat
* Direct calorimetry – measurement of heat
* Body produces heat during exercise

direct calorimetry

\

indirect calorimetry

direct calorimetry

* Body temperature increases chamber water temperature


* Expensive and slow
* Great for rest, but not practical/accurate for exercise

indirect calorimetry

* Rate of oxygen consumption (VO2) is proportional to rate of energy expenditure
* Therefore, VO2 is an “indirect” measure of EE
* Roughly 5 kcal/L O2 consumed (substrate dependent)
* Accurate only for steady-state physiology

steady state

refers to functions that remain unchanged over time

Steady state work rate

stable work rate over time

Steady physiologic state

stable physiological function over time (e.g., heart rate)

Steady state work rate

required for and precedes the attainment of steady state physiology

Steady state physiologic functions

only possible during activities (or rest) that are predominantly fueled by aerobic metabolism

open circuit (indirect calorimetry)

subject breaths air from the surrounding atmosphere and expires air back into the atmosphere

closed circuit (indirect calorimetry)

subject breathes to and from a container of air that is not open to the atmosphere - Not typically used in practice

Volume of air inspired (VI)

Measured or calculated from VE (Haldane transformation)

Volume of air expired (VE)

Measured or calculated from VI (Haldane transformation)

Assumed to be 0.2093 (20.93%)

Fraction of O2 in the inspired air (FIO2)

Assumed to be 0.0003 (0.03%)

Fraction of CO2 in the inspired air (FICO2)

Measured with gas analyzer

Fraction of O2 in the expired air (FEO2)

Measured with gas analyzer

Fraction of CO2 in the expired air (FECO2)

Measuring EE: Haldane Transformation

* VI may not equal VE bc VO2 & VCO2 are rarely equal
* However, V of inspired N2 = V of expired N2
* N2 = nitrogen; 79.03% of VI

Haldane transformation

* Used to calculate VI from VE or VE from VI
* Is based on constancy of N2 volumes

Haldane transformation

V I = (V E x FEN2)/FIN2

VO2

* volume of O2 consumed per minute
* Rate of O2 consumption
* Volume of inspired O2 − volume of expired O2

VCO2

* volume of CO2 produced per minute
* Rate of CO2 production
* Volume of expired CO2 − volume of inspired CO2

volume air inspired \* fraction of the air that is composed of O2 (VI × FIO2)

Volume of O2 inspired =

volume of air expired \* fraction of the air that is composed of O2 (VE × FEO2)

Volume of O2 expired =

Determination of VO2 and VCO2

VO2 = (VI x FIO2) – (VE x FEO2)

Determination of VO2 and VCO2

VCO2 = (VE x FECO2) – (VI x FICO2)

type of fuel being oxidized

(Respiratory Exchange Ratio) O2 usage during metabolism depends on the ___________

Respiratory Exchange Ratio

* More carbon atoms in molecule = more O2 needed
* Glucose (C6H12O6) < Palmitic Acid (C16H32O2)

Respiratory Exchange Ratio (RER)

* Ratio between rates of CO2 production and O2 usage
* _____ = VCO2/VO

0\.71

RER = ____ when Kcal from fats is 100%

1\.0

RER = ____ when Kcal from carbs is 100%

1\.0

RER for 1 molecule glucose =

0\.70

RER for 1 molecule palmitic acid =

energy at rest

* Metabolic rate is the rate of energy use by the body.
* Almost 100% of ATP is produced by aerobic metabolism
* Blood lactate levels are low (

0\.25 L/min

absolute resting O2 consumption

3\.5 mL/kg/min

relative resting O2 consumption

Basal metabolic rate (BMR)

rate of energy expenditure at rest

Basal metabolic rate (BMR)

* In supine position
* Thermoneutral environment
* After 8h of sleep and 12h fasting
* Minimum energy requirement for living

Resting metabolic rate (RMR)

* Like BMR, but less stringent
* Typically, within 5-10% of BMR

Factors that Affect BMR

* Age – BMR with age
* Body temperature – BMR ↑ with ↑ temp
* Psychological stress – stress ↑ SNA ↑ BMR
* Hormones – some hormones ↑ BMR (e.g., epi)

combination of fats and carbs

substrate use during rest

0\.78 – 0.80

values RER at rest

body is using more carbs; increases intensity and increases RER

What happens to RER as physical activity or exercise intensity increases

Total Daily Energy Expenditure (TDEE)

* Includes normal daily activities
* Normal range: 1,800 – 3,000 kcal/day
* Value may be > if you’re regularly exercising
* Competitive athletes: up to 10,000 kcal/day!

Activity Thermogenesis

Greatest source of variability in energy expenditure (within and between individuals)

Activity Thermogenesis

Can account for 15% (sedentary) to 50% (highly active) of total daily energy expenditure

Activity Thermogenesis

* Vigorous exercise can increase energy expenditure 10x (or more) above resting values
* But, non-exercise activity thermogenesis (NEAT) is the predominate component

Metabolic Equivalents (MET)

Classification of physical activity by energy expenditure

Metabolic Equivalents (MET)

* Multiples of resting metabolic rate (RMR)
* 2 METs = 2x RMR, 3 METs = 3x RMR, etc.
* MET approximately = 3.5 ml/kg/min

Energy Expenditure During Submaximal Aerobic Exercise

Exercise increases the energy required in excess of RMR

Slow component of O2 uptake kinetics (submaximal aerobic exercise)

* At high power outputs, V O2 continues to increase beyond typical 1-2 min required for steady state
* More type II (less efficient) fiber recruitment occurs.

VO2 drift (submaximal aerobic exercise)

* Upward drift observed during prolonged, submaximal constant power output exercise
* Possibly due to increased ventilation or hormones?

intensity Metabolism ↑ in direct proportion to ↑ in exercise intensity

submaximal aerobic exercise

At higher work rates, the oxygen consumption (VO2) continues to increase

VO2max (maximal O2 uptake) (Energy Expenditure During Maximal Aerobic Exercise)

* Point at which O2 consumption doesn’t increase with further increases in intensity
* Best single measurement of aerobic fitness

Improvement plateaus after 8 to 12 weeks of training (Energy Expenditure During Maximal Aerobic Exercise)

* Performance continues to improve
* More training allows athlete to compete at higher percentage of VO2max

Energy Expenditure During Maximal Aerobic Exercise

Measured during “incremental exercise to exhaustion” with an exercise mode that uses a lot of muscle mass (typically running)

Energy Expenditure During Maximal Aerobic Exercise

* As maximal effort approaches, VO2 may “plateau” (fail to increase) despite continued increases in work rate
* The extra energy needed to perform the higher work rate is provided by anaerobic metabolism

Energy Expenditure During Maximal Aerobic Exercise

VO2max expressed in L/min

VO2max normalized for body weight

* ml O2 / kg / min
* More accurate comparison for different body sizes
* Untrained young men 44-50 versus untrained young women 38-42
* Difference due to women’s lower FFM and hemoglobin

RER > 1.0

Occurs during high-intensity exercise (non-steady state)

RER > 1.0

Violates the rule of 0.70-1.0 for RER (from table)

RER > 1.0

CO2 production may not = CO2 exhalation

RER > 1.0

As lactate buildup ↑ CO2 exhalation ↑

RER > 1.0

* Caused by “non-metabolic” CO2 production from sources other than macronutrient oxidation
* CO2 from bicarbonate (HCO3-) buffering of acid occurs at a high rate during intense exercise:
* H+ + HCO3- ↔ H2CO3 ↔ H2O + CO2

0\.78-.80

normal range for RER

fat

what substrate is primarily used for RER?

1\.0

RER for 100% CHO

0\.71

RER for 100% fat

0\.2093

assumed FIO2

0\.0003 or 0.03%

assumed FICO2

cardiorespiratory fitness

VO2max often used as a measure of

central factors of cardiorespiratory fitness (determinants of VO2)

* Lungs/airways to move O2 from ambient air to blood
* Heart/blood/circulation to provide oxygenated blood from lungs to tissues

peripheral factors of cardiorespiratory fitness (determinants of VO2)

Tissues (mainly skeletal muscle) to take up and use oxygen to produce ATP

Energy Expenditure During Maximal Aerobic Exercise

* Remember that no activity is 100% aerobic or anaerobic (mixture of metabolic systems with considerable overlap)
* Estimates of anaerobic effort involve
* Excess postexercise O2 consumption (EPOC)
* Lactate threshold (LT)

greater >

* At onset of exercise: O2 demand _____ O2 consumed
* Aerobic metabolism is “slow to get going” (1-2 min)
* Anaerobic metabolism makes up the difference

O2 deficit

* The difference between the O2 required for a given exercise intensity (steady state) and the actual oxygen consumption
* Creates an “O2 debt” that must be consumed after exercise ends, to rectify what was disrupted by anaerobic metabolism (now called EPOC)

Excess Post-Exercise Consumption

After exercise cessation, oxygen consumption exceeds oxygen demand (your body is consuming more O2 per minute than is needs to perform the function since exercise has stopped)

Excess Post-Exercise Consumption

* O2 needs drop rapidly because ATP hydrolysis & production drop rapidly when muscle contraction stops
* VO2 decreases slowly

excess post-exercise O2 consumption

Extra O2 consumed is called

EPOC

used to repay the O2 deficit incurred

EPOC

* O2 is needed for metabolism to:
* Replenish ATP/PCr stores
* Convert lactate to glycogen (gluconeogenesis)
* Replenish hemoglobin and myoglobin with O2
* Clear CO2 from blood (work of ventilation)

EPOC

Magnitude of _____ after high-intensity exercise is a crude index of how much anaerobic metabolism was used for ATP production during exercise

Submaximal (steady state)Exercise

Magnitude and duration of EPOC are influenced by intensity of exercise

Maximal (non-steady state) Exercise

* Magnitude and duration of EPOC are influenced by intensity of exercise
* more deficit= more dependent on anaerobic exercise so EPOC is greater

O2 deficit since O2 demand is greater than O2 consumed in early exercise

Occurs when anaerobic pathways are used for ATP production

EPOC

O2 consumed > O2 demand in early recovery

Lactate threshold (LT)

point at which blood lactate accumulation increases markedly

Lactate threshold (LT)

* Lactate production rate > lactate clearance rate
* Interaction of aerobic and anaerobic systems
* Not the point at which anaerobic metabolism begins (common misconception)
* Good indicator of potential for endurance exercise

Lactate Threshold

Usually expressed as percentage of V O2max

higher lactate threshold

= better endurance performance

* Typically occurs at 50-60% VO2max in untrained individuals
* Elite endurance athletes may not reach until closer to 70-80% of VO2max

lactate threshold

For two athletes with same V O2max, higher ________________ generally predicts better performance

economy of exercise

As athletes become more skilled, they use less energy for a given pace

Energy of Exercise

* Is truly independent of V O2max
* Body learns energy economy with practice
* Lower VO2 for a given activity implies > economy

Multifactorial phenomenon of economy of exercise

* Compared with shorter distance runners, marathon runners are shown to be more economical
* Practice lends better economy of movement (form)
* Varies with type of exercise (running vs. swimming)

Economy of Exercise – Walking

* Among healthy adults, walking economy varies minimally because walking is a skill that most people have mastered
* Economy is low in some conditions
* Movement disorders (e.g. cerebral palsy)
* Older age

1. High V O2max
2. High lactate threshold (as % V O2max)
3. High economy of effort
4. High percentage of type I muscle fibers

Physiological Predictors of Endurance Performance