Energy Costs
of
Physical Activity
1
When Health Fitness Instructors (HFI) recommend specific
physical activities to participants, they are usually concerned
the following 2 questions.
Are the activities appropriate, in term of exercise intensity,
to achieve the target heart rate?
Is the combination of intensity and duration appropriate for
achieving an energy expenditure goal to balance or exceed
caloric intake?
To answer these questions the HFI should become familiar
with the energy costs of various activities
2
1. Ways to measure energy expenditure
2. Ways to express energy expenditure
3. Formula for estimating the energy cost of activities
4. Energy requirements of walking, running, cycle ergometer,
and stepping
Oxygen cost of walking
walking on a horizontal surface
walking up a grade
walking at different speeds
Oxygen cost of jogging and running
jogging and running on a horizontal surface
jogging and running up a grade
jogging and running at different speeds
Oxygen cost of cycle ergometry
leg ergometry
arm ergometry
Oxygen cost of bench stepping
3
Ways to measure energy expenditure
Direct calorimetry
A chamber
insulated
water flowing through walls
warm
Heat given off
subject
Water temperature change
Volume of water flowing
through the wall per min
Example
Vol = 20 L/min, Tem increase = 0.5 C
20L/min x 1 kcal/C x 0.5 C = 10 kcal/min
All the energy released from CHO, Fat ???
4
Indirect calorimetry
Estimate energy production by measuring oxygen consumption
Measurement
Carbohydrate
Fat
Protein
Caloric density (kcal/g)
4.0
9.0
4.0
Caloric equivalent of 1L of O2
(kcal /L)
5.0
4.7
4.5
Respiratory quotient (RQ)
(cell level)
Respiratory exchange ratio (R)
(gas exchange)
1.0
0.7
0.8
5
Indirect calorimetry
Closed-circuit spirometry
Open-circuit spirometry
inhale 100% O2
inhale room air
exhaled CO2 is absorbed
exhaled air is collected
Is it good for measuring
exercise O2 consumption?
then what?how to measure
the following:
rest O2 consumption
exercise O2 consumption
maximal O2 consumption
6
Ways to measure energy expenditure
The energy required for an activity is calculated on the basis of
a subject’s steady-state oxygen uptake (VO2) measured during
an activity.
VO2 (L / min)
Example: submaximal run on a treadmill, 80-kg man,
ventilation = 60 L/min,
inspired O2 = 20.93%, expired O2 = 16.93%
VO2 (L / min) = 60 L/min x (20.93% - 16.93%)
= 60 L/min x 4%
= 2.4 L/ min
7
VO2 (ml/kg/min)
Example: 80-kg man with a VO2 = 2.4 L/min
VO2 (ml/kg/min) = 2.4 L/min x 1000 ml/L ÷ 80 kg
= 2400 ml/min ÷ 80 kg
= 30 ml/kg/min
METs (metabolic equivalents)
Example: 30 ml/kg/min
1 MET = 3.5 ml/kg/min
METs = 30ml/kg/min ÷ 3.5 ml/kg/min = 8.6 METs
8
Conversion to appropriate unites &
knowledge of common equivalents
Power
Weight
1 MET = 3.5 ml/kg/min
1 kg =2.2 lb
= 1 kcal/kg/hr
1 kg = 1 kp = 9.8 N
= 1.6 km/hr
Speed
= 1.0 mi/hr
1 mi/h = 26.8 m/min
1 watt = 6.0 kg/m/min
Distance
1 mi = 1.6 km
Work
1 L O2 = 5 kilocalories (kcal)
3500 kcal = approximately 1 lb of fat gain or loss
1 kg.m = 1.8 ml O2
9
Formula for estimating the energy cost of activities
Total O2 cost = sum of energy components
= net O2 cost of activity + 3.5 ml/kg/min
Total cost of grade walking
= net O2 cost of the horizontal walk
+ net O2 cost of the vertical
+ resting metabolic rate (1 MET = 3.5 ml/kg/min)
Subject must follow instructions carefully - do not hold on to the
treadmill railing; maintain the pedal cadence
Work instruments (treadmill; ergometer) must be calibrated
10
Energy requirements of
walking, running, cycle ergometer, and stepping
O2 cost of walking on a horizontal surface
* walking speeds of 50 and 100m/min or 1.9 to 3.7 mi/hr
(mi/h x 26.8 = m/min or m/min ÷ 26.8 = mi/hr)
* ACSM (1995) the formula can be used for speed faster than
3.7 mi/hr as long as the person is truly walking, not jogging or
running.
VO2 = 0.1 ml/kg/min x (horizontal velocity, m/min) + 3.5 ml/kg/min
m/min
Net O2 cost of walking 1 m/min on a horizontal surface is
0.100 to 0.106 ml/kg/min. A value of 0.1 ml/kg/min is used
in ACSM equation.
11
What are the estimated steady-state VO2 and METs for a walking
speed of 90 m/min (3.4 mi/hr x 26.8 = 90 m/min) ?
VO2 = 90 m/min x 0.1 ml/kg/min + 3.5 ml/kg/min
m/min
= 9.0 ml/kg/min + 3.5 ml/kg/min
= 12.5 ml/kg/min
METs = 12.5 ml/kg/min ÷3.5 ml/kg/min = 3.6 MTEs
Can the formula be used to predict the level of activity required to
elicit a specific energy expenditure? YES. See the next example
12
An unfit participant is told to exercise at 11.5 ml/kg/min to
achieve the proper exercise intensity. What walking speed would
you recommend?
11.5 ml/kg/min =
? m/min x 0.1 ml/kg/min + 3.5 ml/kg/min
m/min
11.5 ml/kg/min - 3.5 ml/kg/min =
? m/min x 0.1 ml/kg/min
m/min
8 ml/kg/min = ? m/min x 0.1 ml/kg/min
m/min
? m/min = 8 ml/kg/min ÷ 0.1 ml/kg/min = 80 m/min
m/min
80 m/min ÷ 26.8 = 3.0 mi/hr
13
O2 cost of walking up a grade
sum of O2 cost of horizontal walking
O2 cost of vertical component
resting metabolic rate
VO2 = 0.1 ml/kg/min x (horizontal velocity, m/min)
m/min
+ 1.8 ml/kg/min x (vertical velocity) + 3.5 ml/kg/min
m/min
*O2 cost of moving (walking or steeping) 1 m/min vertically
= 1.8 ml/kg/min
*Vertical velocity = grade (?%) x speed m/min
14
What is the total O2 cost of walking 90 m/min up a 12% grade?
Horizontal component = 90 m/min x 0.1 ml/kg/min = 9.0 ml/kg/min
m/min
Vertical component = 12% x 90 m/min x 1.8 ml/kg/min
m/min
= 19.4 ml/kg/min
VO2 (ml/kg/min) =9.0 (horizontal) + 19.4 (vertical) + 3.5 (rest)
= 31.9 ml/kg/min
METs = 31.9 ml/kg/min ÷ 3.5 ml/kg/min = 9.1 METs
15
To estimate the setting needed to elicit a specific O uptake
Set the treadmill grade to achieve an energy requirement of 6 METs
(21.0 ml/kg/min) when walking at 60 m/min
Net O2 cost of the activity = 21 - 3.5 = 17.5 ml/kg/min
Horizontal component = 60 m/min x 0.1 ml/kg/min = 6.0 ml/kg/min
m/min
Vertical component = 17.5 - 6.0 = 11.5 ml/kg/min
11.5 ml/kg/min = grade x 60 m/min x 1.8 ml/kg/min
m/min
= grade x 108 ml/kg/min
Grade = 11.5 ÷ 108 = 0.106 x 100% = 10.6%
16
O2 cost of walking at different speeds
Beyond walking speed of 50 - 100 m/min (1.9 - 3.7 mi/hr),
O2 requirement for walking increases in a curvilinear manner.’
Many people chose to walk at a fast speed rather than jog.
Table 7.2 p133
17
Energy cost of walking expressed in kcal/min
T7.3 p133
Energy cost of walking increases with the speed of the walk,
the rate of increase is higher at the higher speed.
Example: 170-lb participate
speed
2 to 3 mi/hr
O2 cost ___ to ____ Kcal/min
4 to 5 mi/hr
___ to ____ Kcal/min
18
O2 cost of jogging and running
for speed of 130 - 350 m/min (4.85 - 13 mi/hr)
O2 cost of jogging and running on a horizontal surface
VO2 = 0.2 ml/kg/min x (horizontal velocity, m/min) + 3.5 ml/kg/min
m/min
Net O2 cost of jogging or running 1 m/min on a horizontal surface is
about twice that of walking, 0.2 ml/kg/min.
What is the O2 requirement for running a 10K race
on a track in 60 min?
10K = 10,000 m
10,000m ÷ 60 min = 167 m/min
VO2 = 167 m/min x 0.2 ml/kg/min + 3.5 ml/kg/min
m/min
= 36.9 ml/kg/min
METS = 36.9 ml/kg/min ÷ 3,5 ml/kg/min = 10.5 METS
19
A 20-year-old female distance runner with a VO2max of
50 ml/kg/min wants to run intervals at 90% of VO2max.
At what speed should she run on a track given that one mile
equals 1610m?
90% x 50 ml/kg/min = 45 ml/kg/min
VO2 = 0.2 ml/kg/min x (horizontal velocity, m/min) + 3.5 ml/kg/min
m/min
45 ml/kg/min = 0.2 ml/kg/min x (horizontal velocity) + 3.5 ml/kg/min
m/min
45 ml/kg/min - 3.5 ml/kg/min = 0.2 ml/kg/min x (horizontal velocity)
m/min
41.5 ml/kg/min = 0.2 ml/kg/min x (horizontal velocity)
m/min
speed = 41.5 ml/kg/min ÷ 0.2 ml/kg/min = 207 m/min
m/min
1610 m ÷ 207 m/min = 7.78 min, (60”x 0.78 = 47”), 7:47” mi pace
20
O2 cost of jogging and running up a grade
Net O2 cost of jogging or running 1 m/min on a horizontal surface is
about twice that of walking, 0.2 ml/kg/min.
O2 cost of running up a grade is about one half that of walking
up a grade, O2 cost of running 1 m/min vertically is about
0.9 ml/kg/min
VO2 = 0.2 ml/kg/min x (horizontal velocity, m/min)
m/min
+ 0.9 ml/kg/min x (vertical velocity) + 3.5 ml/kg/min
m/min
What is the O2 cost of running 150 m/min up a 10% grade?
Horizontal components = 0.2 ml/kg/min x 150 m/min = 30 ml/kg/min
m/min
Vertical component = 0.9 ml/kg/min x (10% x 150 m/min)
m/min
= 13.5 ml/kg/min
VO2 = 30.0 (horizontal) + 13.5 (vertical) + 3.5 (rest) = 47 ml/kg/min =13.4 METs
21
The O2 cost of running 350m/min on a flat surface is about
73.5 ml/kg/min. What grade should be set on a treadmill for
a speed of 300 m/min to achieve the same VO2?
Horizontal components = 0.2 ml/kg/min x 300 m/min = 60 ml/kg/min
m/min
Vertical component = 73.5 (total) - 60 (horizontal) - 3.5 (rest)
= 10.0 ml/kg/min
Also, Vertical component = 0.9 ml/kg/min x (vertical velocity)
m/min
Hence, 10.0 ml/kg/min = 0.9 ml/kg/min x (vertical velocity)
m/min
= 0.9 ml/kg/min x (grade x speed )
m/min
= 0.9 ml/kg/min x (grade x 300m/min )
m/min
= 270 ml/kg/min x grade
Grade = 10 ml/kg/min ÷ 270 ml/kg/min = .037 = 3.7 % grade
22
O2 cost of jogging and running at different speeds
In contrast to walking, the energy cost of jogging and running
increases in a linear and predictable manner with increasing speed
T7.4-7.5 p136
23
O2 cost of cycle ergometry
* body weight is supported by the cycle
* work rate is determined primarily by the pedal rate and the
resistance on the wheel
* O2 requirement in liters per minute is approximately the same
for people of different sizes for the same work rate. Thus, when
a light person is doing the same work rate as a heavy person, the
relative VO2 (ml/kg/min), or MET level, is higher for the lighter
person.
* The O2 cost of doing 1kpm of work is approximately 1.8 ml.
During cycle exercise, energy must be expended to overcome the
friction (unmeasured work)in the drive train of the cycle. This
additional work requires about 10% of the O2 required to do the
measured work, so 0.2 ml/kpm is added to the 1.8 ml/kpm to
get the net cost per kilopond meter of work on a cycle ergometer
, 2 ml/kpm.
24
VO2 (ml/min) = work rate (kpm/min) x 2ml/kpm
+ (3.5 ml/kg/min x body weight in kg)
Since 6 kpm/min = 1 W (watt),
VO2 (ml/min) = work rate (W) x 6 x 2ml/kpm
+ (3.5 ml/kg/min x body weight in kg)
25
What is the O2 cost of doing 600 kpm/min (100W) on a cycle
ergometer for 50-kg and 100-kg subjects?
VO2 = 600 kpm/min x 2 ml/kg/min + (3.5 ml/kg/min x kg wt)
For the 50-kg subject
VO2 = 1200 ml/min + (3.5 ml/kg/min x 50 kg)
= 1200 ml/min +175 ml/min = 1375 ml/min
1375 ml/min ÷ 50 kg = 27.5ml/kg/min = 7.9 METs
For the 100-kg subject
VO2 = 1200 ml/min + (3.5 ml/kg/min x 100 kg)
= 1200 ml/min + 350 ml/min = 1550 ml/min
1550 ml/min ÷ 100 kg = 15.5 ml/kg/min = 4.4 METs
26
A 70-kg participant must work at 6 METs to match the intensity
of his walking program. What force (load) should be set on a Monark
cycle ergometer at a pedal rate of 50 rev/m?
6 METs =6 x 3.5 ml/kg/min x 70 kg = 1470 ml/min
VO2 (ml/min) = work rate (kpm/min) x 2ml/kpm
+ (3.5 ml/kg/min x body weight in kg)
1470 ml/min = kpm/min x 2 ml/kpm + (3.5 ml/kg/min x 70 kg)
Net cost of cycling = 1470 - (3.5 ml/kg/min x 70 kg)
= 1470 - 245 = 1225 ml/min
1225 ml/min = ? kpm/min x 2 ml/kpm
Work rate (kpm/min) = 1225 ml/min ÷ 2 ml/kpm = 612 kpm/min
612 kpm/min = (50 rev/m x 6m/rev) x force
= 300 m/min x force
Force = 612 kpm/min ÷ 300 m/min = 2.04 or 2.0 kp
27
O2 cost of bench stepping
Total O2 cost is the sum
O2 cost of
stepping up
1.8 ml/kg/min
O2 cost of
stepping down
0.33 x 1.8 ml/kg/min
O2 cost of
moving back and forth
on a surface at the
specified cadence
step rate x 035 ml/kg/min
1.33 x 1.8 ml/kg/min
VO2 = step height (m) x lifts/min x 1.33 x 1.8 ml/kg/min
m/min
+ step rate x 0.35 ml/kg/min
28
What is the O2 requirement for stepping at a rate of
20 steps/min on a 20-cm bench?
VO2 = step height (m) x lifts/min x 1.33 x 1.8 ml/kg/min
m/min
+ step rate x 0.35 ml/kg/min
VO2 = 0.2 m/lift x 20 lifts/min x 1.33 x 1.8 ml/kg/min
m/min
+ 20 x 0.35 ml/kg/min
= 9.6 ml/kg/min + 7.0 ml/kg/min
= 16.6ml/kg/min or 4.7 METs
29