measuring energy expenditure

"DIRECT CALORIMETRY"

fat: 9.4 kcal (bomb calorimeter)

     9 kcal (Atwater)

CHO: 4.2 kcal (BC)

     4 kcal (Atwater)

protein: 5.65 kcal (BC)

         4 kcal (Atwater)

*per gram substrate*

measuring energy expenditure

"INDIRECT CALORIMETRY"

• determines energy expenditure from measurements of oxygen uptake and carbon dioxide production using
• closed-circuit spirometry (calorimetry)
• open-circuit spirometry (calorimetry)
• doubly labeled water technique
• all energy-releasing r(x)s in the body ultimately depend on utilization of oxygen

subject breathes 100% oxygen from a spirometer

"closed system" because the person rebreathes only the gas in the spirometer

a canister of soda lime (KOH) in the breathing circuit absorbs the carbon dioxide in exhaled air

a drum atached to the spirometer revolves at a known speed and records oxygen uptake from changes in the system's volume

gas exchange is determined by comparing volumes of gases inspired to volumes expired

% concentrations of gases in expired and inspired air determined by O₂ and CO₂ analyzers

Δ in oxygen and carbon dioxide percentages in expired air compared to inspired ambient air indirectly reflect the ongoing process of energy metabolism

• all open calorimetry systems determine gas exchange using same basic measurements
• ventilation volumes (V_E and V_I)
• fractional concentration of O₂ and CO₂ in expired and inspired air
• the Δ in O₂ and CO₂ volume between expired and inspired air reflect O₂ utilization and CO₂ production, respectively

RER

respiratory exchange ratio

provides information about the nutrient mixture catabolized for energy

=1.00 for CHO

=0.70 for fat

=0.82 for protein

RER reflects pulmonary exchange of carbon dioxide and oxygen under various physiologic and metabolic conditions

RER may not always accurately relate to the macronutrient mixture being catabolized

RER does not indicate specific substrate utilization during nonsteady state exercise due to nonmetabolic carbon dioxide production in the buffering of lactate

terms which relate amount of exercise dones to energetic cost of exercise

EFFICIENY

terms which relate amount of exercise done to energetic cost of exercise

ECONOMY

term used when work done cannot be measured

usually a measurement of oxygen cost relative to movement velocity is used

eg. running, swimming

basic definitions of mechanical efficiency

GROSS EFFICIENCY

W/E

work accomplished relative to the energy expended to accomplish the work, or rate at which work is done relative to rate at which energy is expended

*gross<net<work*

problems in determining efficiency

COST OF RESTING

problems in determining efficiency

COST OF UNLOADED WORK

basic definitions of mechanical efficiency (base-line subtractions)

NET EFFICIENCY

W/(E-E_R)

work accomplished relative to the energy expended to accomplish the work minus resting energy cost

rate at which work is done relative to rate at which energy is expended minus rate of resting energy expenditure

basic definitions of mechanical efficiency (base-line subtractions)

WORK EFFICIENCY

W/(E-E_u)

work accomplished relative to the energy expended to accomplish the work minus the energy cost of unloaded work

rate at which work is done relative to rate at which energy is expended minus rate of unloaded energy expenditure

mechanical efficiengy of a mechanically braked cycle ergometer

(need whiteboard, see slide 24)

mechanical efficiency of a mechanically braked cycle ergometer

(need whiteboard, see slide 26)

exercise work rate: efficiency decreases as work rate increases?

speed of movement: there is an optimum speed of movement and any deviation reduces efficiency

fiber composition of muscles: higher efficiency in muscles with greater percentage of slow twitch fibers

as WR ↑, energy expenditure ↑

[image]

[image]

in this example, optimal movement speed for 150W is at peak of curve

optimal movement speed varies with WR

not possible to calculate efficiency of some forms of movement, ie. horizontal running and swimming

movement economy:

oxygen cost of moving at a given speed

lower VO₂ (mL/kg/min) per unit of speed indicates better movement economy

between 70-80 ml/kg/min of maximal aerobic power (aka good runners) there is less correlation than there is between less skilled runners

*runner A was the more economical, and therefore, the faster runner*

[image]

for elite swimmers, as swimming velocity increased, VO₂ greatly increased more than any other swimming group

[image]

estimation of energy expenditure

energy cost of horizontal treadmill walking or running

expression of energy cost

1 MET = cost of energy at rest

1 MET = 3.5 ml/kg/min

exercise between estimation lines (aka gap) cannot be adequately estimated using ACSM formulas

[image]

linear relationship between VO₂ and walking or running speed

(need whiteboard, see slide 38)

transform VO₂ into the most appropriate units:

weightbearing activity: convert to ml/kg/min

non-weightbearing activity: convert to ml/min

involes caloric expenditure/weight los: convert to L/min

write the appropriate equation in the form VO₂ = R + H + V

R= resting component

H= horizontal component

V= vertical component

see closer look 6.1 in text

16-32 min/mi pace

[image]

see closer look 6.2 in text

<12 min/mi pace 

[image]

appropriate for WR 50-100W

R= 3.5 ml/kg/min

H= 0, there is no horizontal component

V= W/m x 10.8 + 3.5 ml/kg/min

where: W= WR in W

m= mass in kg

VO₂ (in ml/kg/min) = R+H+V

VO₂ (in ml/kg/min) = W/m x 10.8 + 7.0 ml/kg/min

*7.0 ml/kg/min comes from 3.5 for rest and 3.5 for unloaded* 

unit of energy measurement

the quantity of heat necessary to raise the temperature of 1 ml of water 1°C

the Calorie (kcal) = 1000 calories, aka the amount of heat needed to raise 1L of water 1°C