energy expenditure
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Energy Expenditure at
Rest & Physical Activity
McArdle, Katch, & Katch
Chapter 8
Energy Expenditure at Rest
Basal Metabolic Rate
BMR is rate of energy expenditure fasted, rested and
supine conditions in thermoneutral environment.
Resting Metabolic Rate (RMR) is rate of energy
expenditure when at rest but not basal (> BMR).
BMR proportional to BSA, after age 20 2% & 3%
per decade in women and men, respectively
When RMR expressed per unit LBM, no difference
BMR represents largest fraction of TEE in sedentary
Energy Expenditure at Rest
Influence of Body Size
Differences in body size usually expressed in terms
of body surface area (BSA).
From 20-40, average values BMR are 38 kcal/m2 per
hour for men and 36 kcal/m2 for women.
Lower BMR in women can be attributed to woman’s
larger percent body fat & smaller muscle mass.
Energy Expenditure at Rest
Estimate Resting Daily
Energy Expenditure
Estimate kcal expenditure
during rest by multiplying
one’s surface area from
nomogram by appropriate
kcal expenditure/m2 per
hour by 24 hrs.
Also possible to use Harris
Bennedict formulas.
Estimated values w/i ± 5%
measured values.
Energy Expenditure at Rest
Components of Total Daily
Energy Expenditure
Physical Activity: 15-30% of
TDEE
Dietary Induced Thermogenesis
(~10% TDEE)
Thermic effect from processes of
digesting, absorbing, &
assimilating nutrients.
Thermogenesis reaches maximum
w/i 1 hr post
Thermogenesis can vary 10%-
35% of ingested food energy
Resting Metabolic Rate
Energy Expenditure at Rest
Factors affecting Total
Daily Energy Expenditure
Climate.
RMR of people in
tropic climate averages
5-10% higher.
RMR in extreme cold
can triple.
Pregnancy.
Energy Expenditure in Physical
Activity
Expression of Energy Expenditure
Total (gross) – Resting energy expenditure (REE) =
Net energy cost of the activity per se.
Recovery energy included in Total = exercise energy
+ recovery energy.
Utilization of 1 liter of O2 generates about 5 kcal of
energy.
Net O2 cost of exercise = exercise VO2 + recovery
VO2 – (resting VO2 x time)
Energy Expenditure in Physical
Activity
Energy expended during weight-bearing activities increases proportional to body mass.
There is little relationship between body mass and energy expended during non-weight-bearing activities.
Energy Expenditure in Physical Activity
Average daily Total Energy Expenditure estimated to
be 2900 – 3000 kCal for males, and 2200 kCal for
females 15-50 y.o.a.
Great variability exists because of one’s physical
activity; average person spends ___% day sedentary.
Energy Expenditure in Physical
Activity
Classification of Work Factors:
Duration (min) and Intensity (VO2 & kCal)
A MET is a measure of activity intensity & represents
an average person’s resting metabolism or VO2
1 MET =
3.5 mlkg-
1min-1
Energy Expenditure in Physical
Activity
Classification of Work
Intensity of Work often
related to Heart Rate
because of linear
relationship to oxygen
uptake.
Economy & Efficiency of Energy
Expenditure
Mechanical Efficiency = Work Output ÷
Energy Input (expenditure).
Work Output = Force x Distance
kg m or ft lb.
Three efficiency terms:
1. Gross
2. Net
3. Delta
Economy & Efficiency of Energy
Expenditure
Gross efficiency uses total oxygen uptake.
Work Output
Energy Expended
Net efficiency subtracts resting VO2 from total.
Work Output
Energy Expended Above Rest
Delta efficiency computes relative energy cost of
performing an additional increment of work.
Energy Expenditure during Walking,
Running, and Swimming
Economy is relationship between
Energy output
Energy input
Greater economy requires less oxygen uptake to
perform a task.
Training adjustment that improves economy
directly relates to improved exercise
performance.
Energy Expenditure during Walking,
Running, and Swimming
Energy Expenditure during
Walking
Relationship between walking
speed and oxygen uptake
essentially linear between
speeds of 3.0 and 5.0
kilometers per hour (1.9 to
3.1 mph).
At faster speeds, walking
becomes less economical and
relationship curves in upward
direction.
Energy Expenditure during Walking,
Running, and Swimming
Walking on snow and sand requires about twice the energy expenditure of walking on hard surfaces.
Energy cost is proportionally larger for larger people.
Hand-held weights increases energy cost of walking but may disproportionately elevate systolic blood pressure.
Energy Expenditure during Running
More economical to discontinue walking and begin
to run or jog at speeds > 6.5 kmh (4 mph).
Net energy cost of running a given distance is
independent of speed (pace).
Lengthening stride above the optimum length (and
reducing stride frequency) increases VO2 more than
shortening below optimum (and increasing stride
frequency).
Cost of running into headwind significantly greater
than the reduction with tailwind.
Energy Expenditure during
Swimming
Energy expenditure to swim a given distance is
about 4 times greater than to run same distance.
Energy must be expended to maintain buoyancy
while generating horizontal motion and to
overcome drag forces.
Total drag consists of:
Wave drag
Skin friction drag
Viscous pressure drag
Energy Expenditure during
Swimming
Elite swimmers expend
fewer calories to swim a
given stroke at any
velocity.
Women swim a given
distance at lower energy
cost than men because of
greater buoyancy.
Illustration Reference
McArdle, William D., Frank I. Katch, and Victor
L. Katch. 2006. Essentials of Exercise Physiology
3rd ed. Image Collection. Lippincott Williams &
Wilkins.