Energy Expenditure and Fatigue

basal metabolic rate

rate of energy expenditure for an individual in supine position, measured in a thermoneutral environment immediately after 8 hours of sleep and at least 12 hours of fasting

Average range: 1200 - 2400 kcal/day

calorie

basic unit of heat

calorimeter

insulated, air-tight chamber that contain copper tubing throught which water is circulated. Heat produced by the body radiates to the walls and heats the water

direct calorimetry

measuring body's heat production to gauge the rate and quantity of energy production; uses a calorimeter

excessive post-exercise oxygen consumption

volume of oxygen consumed during the minutes immediately after exercise ceases that is above normally consumed at rest

fatigue

general sensations of tiredness and accompanying decrement in muscular performance; inability to maintain required power output to continue muscular work at a given intensity

Haldene transformation

an equation allowing one to calculate the inspired air volume from expired air volume or expired air volume from inspired air volume

volume of nitrogen inspired is equal to volume of nitrogen expired

indirect calorimetry

energy expenditure measured by measuring exchange of respiratory gases produced via oxidative metabolism (rates of O2/CO2 exchanged in lungs equals rate of their usage and release by body tissue)

lactate threshold

the point at which blood lactate begins to substantially accumulate above resting concentrations during exercise of increasing intensity

Normal levels 0.8-2.5 mmol/L

maximal oxygen uptake (VO2max)

maximal limit of one's ability to increase VO2 (aerobic capacity)

* Normally active untrained college-aged students = 38-42 ml/kg/min

peak oxygen uptake (VO2peak)

highest oxygen uptake achieved

respiratory exchange ratio

ratio between rate of CO2 release (VCO2) and oxygen consumption (VO2)

RER= VCO2/VO2; at rest=0.78 -0.8

resting metabolic rate

the bodys metabolic rate early in the morning following 8 hours of sleep

average total RMR of an individual engaged in normal daily activity = 1800-3000

Vo2 drift

a slow increase in VO2 during prolonged, submaximal, constant power output activity; observed well below lactate threshold, magnitude of increase of VO2 drift is much less than VO2max

How is RER used to determine oxidation of fats and carbohydrates

The amount of O2 used during metabolism depends on the type of fuel being oxidized; in general the amount of O2 needed to oxidize a molecule of CHO or Fat is proportional to the amount of carbon in that fuel. By finding how much CO2 molecules is released compared to amount of O2 released we can calculate RER

Carb: 1.0

Fat: 0.7

Protein: 0.82

How is maximal O2 uptake measured and what is its relationship to sport performance?

Vo2max can be estimated by submaximal and maximal test, direct and indirect calorimetry

Vo2max is a good predictor of success in endurance events and increases with training (5-20%). The more oxygen you can take in and use at higher levels, the more ATP you can produce through oxidative system, thereby delaying fatigue

Two possible markers of anaerobic capacity

blood lactate threshold: higher blood lactate threshold indicates being able to exercise for longer periods before fatiguing

EPOC: EPOC as an indicator of the amount of anaerobic activity that had occured (shows the amount of lactic acid in tissues, that needs to be removed in order to store depleted glycogen stores --> glycogen used in anaerobic glycolysis

How is lactate threshold measured and whats its relationship to sport performance

blood lactate samples; increases as intensity increases; reflects interaction between aerobic and anaerobic energy systems; ability to exercise at high intensities without accumulating lactate is beneficial to athletes because lactate accumulation contributes to fatigue; LT is major determinant of pace that can be tolerated during a endurance event

How is economy of effort measured and what is its relationship to sport performance?

no way to measure economy; high economy of effort mean using less energy during activity and therefore being able to exercise for longer periods of time

What is the relationship between O2 consumption and energy production?

O2 is required to breakdown substrates for energy; increased 02 consumption means being able to break down more substrate and being able to break down substrates quicker .:. being able to provide more energy for exercise and burning more calories

Why do athletes with high Vo2max values perform better in endurance activities than those with lower values?

ability to perform at a higher VO2max and being able to maintain VO2 max (or a % of Vo2max) for prolonged times indicates that the individual is able to take in more oxygen to be converted into energy for endurance activity

Possible causes of fatigue 1) 15-30 sec. and 2) 2-4 hours

1) PCr depletion, ATP decreasing, muscle glycogen depletion, possibly lactic acid accummulation --> increased muscle acidosis (increased H+), Failure of muscle fiber's contractile mechanism

2) glycogen depletion, increased muscle temperature, loss of water (dehydration) and electrolytes (high body T)

Three mechanisms through which lactate can be used as an energy source

1) can be taken up in mitochondria and directly oxidized

2) Lactate shuttle: transported to other cells for oxidization

3) transported by the blood to the liver, where it is reconverted into pyruvic acid

O2 and CO2 measurement volumes

expired O2 concentration is less than the inspired

CO2 concentrations are higher in expired air than in inspired