energy Measuring expenditure
Calorie
The amount of energy that raises one gm of H2O one degree C. Very small unit, thus we report kilocalories (kcal) = 1000 calories.
Example: A snickers bar has about 200 kcal of energy Conversion to Joules: 1 kcal = 4186 Joules
Metabolism The sum of all transformations of energy and matter that goes on within an organism. Basal metabolic rate (resting daily energy expenditure): Energy expended over 24 hours for a person in the "resting" state.
e.g., your book gives a value of 1471 kcal per 24 hour for an average college aged woman. How many snickers bars to support her basal EE?
Exercise Energy Expenditure EE can rise dramatically with physical activity
e.g., the woman above running at a strong pace for 1 hour could expend as much as 900 kcal/hr. Compare to her resting EE per hour: Athletes training very hard?
Riders in the Tour de France?
Question: How can we measure the sum of all transformations of energy and matter that goes on within an organism in order to quantify BMR or EE during exercise? Answer: We cannot!
Functional definition: metabolism is the rate of heat production. Direct calorimetry: the measurement of heat at rest or during physical activity.
Indirect calorimetry: the measurement of something else.
Measuring metabolic rate: the total energy metabolism by an animal per unit time.
The metabolic "black-box"
Direct calorimetry
Open circuit indirect calorimetry
Budgerigar, parakeet.
Oxygen consumption (VO2): An indirect measure of energy expenditure Units: liters O2/min., or ml O2/min.
Good measure, if ATP is produced by oxidation (i.e., TCA cycle) of fat, carbohydrate, protein. Not so good if glycolysis contributes a significant amount of ATP during exercise. Do you understand why?
Consider the VO2 onset kinetic i.e., what happens to VO2 when exercise begins?
Exercise Steady state
2
VO2
1
Resting steady state
0 0 2 4 6 8 10 12
Time
When is VO2 a very poor of measure energy expenditure?
How exactly is VO2 used to estimate energy expenditure in kcals?
For example, what does it mean in energetic terms to consume1 liter of O2/min while jogging?
Bomb calorimeter measures the energetic value of 1 gram of fat, carbohydrate, or protein.
Carb. Fat Protein
kcal/gram kcal/liter O2 ~4 5.05 ~9 4.7 ~4 4.5
The values given as kcal/liter O2 are termed the energetic equivalents of carb., fat, etc...
How do you determine what fuel is being used during exercise in order to calculate an accurate EE based on a VO2 measurement?
Consider the chemical equation for the full oxidation of carbohydrate versus fat. Carbohydrate?
FFA (trioleate)? C57H104O6 + 80 O2 --> 57 CO2 +52
*The respiratory quotient RQ=VCO2/VO2 can be used to determine the relative contribution of FFAs and Carbohydrate to energy metabolism.
What happens to RQ (RER) with increasing exercise intensity?
Often, the RQ goes higher than 1.O Is this theoretically possible given that the RQ for pure carb is 1.0, and the RQ for pure fat is about 0.71?
Must distinguish between the RQ and the respiratory exchange ratio (RER). The RER takes into account the fact that some of the CO2 produced during exercise is not metabolic in origin.
Not metabolic? Where does it come from?
Brief Introduction to the blood gas buffering system: A buffer system consists of an acid and its dissociated components. What is pH? When pH increases? When pH decreases?
Bicarbonate buffer system: CO2 + H20 H2CO3 H+ + HCO3-
***The main way that pH is regulated in the blood is by ventilation: ventilation affects pH by changing the CO2 content of blood***
Loss of CO2 by hyperventilation
Example: buffering a metabolic acid (lactic acid) HLA - H+ + LAH+ + HCO3- - H2CO3 H2CO3 - H20 + CO2
The onset of blood lactate accumulation (OBLA), lactate threshold, anaerobic threshold.
The OBLA should be evident from respiratory data
6 5 4 3 2 1 0 0 10 Time 20 30 VO2 VCO2
L/min