1. Energy Costs of Physical Activity
C H A P T E R 6
Energy Costs of Physical Activity
Edward T. Howley
Chapter 6

2. Physical Activity of Your Client
How can the current activity be tracked?
Is the intensity appropriate for achieving THR?
Is the volume (energy cost) sufficient for health gains? (see chapter 11)
Is the volume (energy cost) sufficient for weight management?

3. Tracking Physical Activity: Strengths and Weaknesses of Each
Self-reported levels
Pedometer
Accelerometer
Heart rate monitoring

4. Relating PA and Health Outcomes Across All Tracking Methods
Energy expended (i.e., kcal)
Convert measured PA levels

5. Measuring Energy Expenditure
Direct calorimetry
Transfer of body heat to water
Indirect calorimetry
Measure VO2 uptake
Convert VO2 to kcals

6. Indirect Calorimetry: Caloric Density of CHO, Fat, Protein
CHO, fat, or protein completely oxidized to CO2 and H20
Different amounts of O2 are required to completely oxidize substrates
Heat released
Substrate
Heat released (kcal of heat/gram)
CHO
4.0
Fat
9.0
Protein (physiological value)
Water

7. Indirect Calorimetry: Caloric Equivalent of Oxygen
Caloric equivalent of O2 (kcal/LO2)
Calories of energy produced when 1 LO2 is consumed
Substrate
Kcal/LO2
CHO
5.0
Fat
4.7
Protein
4.5
6% more energy produced with CHO as fuel
At 60% to 80% VO2max, the average kcal produced per LO2 is Round up to 5.0.

8. Measuring Oxygen Uptake: Closed Circuit
Breathe in 100% O2
Exhaled CO2 absorbed by chemical
100% O2
Over time, O2 in spirometer decreases, and we can measure O2 consumed.
Some O2 consumed by the body; remaining O2 returns to spirometer

9. Measuring O2 Consumption: Open Circuit (most common method)
O2 inhaled – O2 exhaled = O2 consumed
Exhaled CO2 is also calculated, and from this we can calculate R and thus fuel used

10. Expressing Energy Expenditure
VO2 (L/min)
Also called absolute VO2
Kcal/min
VO2 (ml  kg-1  min-1)
Also called relative VO2
METs
Metabolic equivalent; describes a standard or reference
1 MET = 3.5 ml  kg-1  min-1
Kcal  kg-1  hr-1

11. Calculating Volume (Amount) of Physical Activity
10 kcal/min x 30 min = 300 kcal
7 METs x 30 min = 210 MET min
500 to 1000 MET minutes per week equates to health benefits

12. Equations to Estimate Energy Cost of Activity
Assume no handrail holding
Doing so would overestimate VO2
Assume similar running economy
Formula will overestimate VO2 for trained runners
Assume steady state
Formula estimate
Typical standard deviation of 7% to 9%
Assume calibrated machinery

13. Energy Cost of Activity: Common Weight-Bearing Activity
Oxygen cost
Walking
Horizontal
0.1 ml  kg-1 ∙ min-1/ m  min-1
Vertical
1.8 ml  kg-1  min-1/ m  min-1
Jogging/running
0.2 ml  kg-1  min-1/ m  min-1
0.9 ml  kg-1  min-1/ m  min-1
Stepping
0.2 ml  kg-1  min-1/ steps  min-1
1.8 ml  kgm-1

14. Estimating the Energy Cost of Walking (for speeds of 1.9 to 3.7 mph)
Gross VO2
Net VO2
Resting VO2
Horizontal component
Vertical component
3.5 ml  kg-1  min-1
This equation calculates VO2 in the units of ml  kg-1  min-1

15. Estimating the Energy Cost of Walking (for speeds of 1.9 to 3.7 mph)
Gross VO2
Net VO2
Resting VO2
(0.1)(S)
(1.8)(G)
3.5 ml  kg-1  min-1
(S) = speed in m/min; (G) = grade expressed as a fraction

16. This equation calculates VO2 in the units of ml  kg-1 min-1
Estimating the Energy Cost of Jogging/Running (for speeds of 4.8 to 13 mph)
Gross VO2
Net VO2
Resting VO2
Horizontal component
Vertical component
3.5 ml  kg-1 min-1
This equation calculates VO2 in the units of ml  kg-1 min-1

17. Estimating the Energy Cost of Jogging/Running (for speeds of 4
Estimating the Energy Cost of Jogging/Running (for speeds of 4.8 – 13 mph)
Gross VO2
Net VO2
Resting VO2
(0.2)(S)
(0.9)(G)
3.5 ml  kg-1  min-1
(S) = speed in m/min; (G) = grade expressed as a fraction

18. Estimating the Energy Cost of Stepping
Gross VO2
Net VO2
Resting VO2
Horizontal component
Vertical component
3.5 ml  kg-1  min-1
This equation calculates VO2 in the units of ml  kg-1 min-1

19. Estimating the Energy Cost of Stepping
Gross VO2
Net VO2
Resting VO2
(0.2)(f)
(1.8)(1.33)(f)(h)
3.5 ml kg-1 min-1
(f) = step frequency in steps/min; (h) = grade expressed as a fraction

20. Energy Cost of Activity: Common Non-Weight-Bearing Activity
Oxygen Cost
Leg ergometry
Loaded
1.8 ml/kgm
Unloaded
3.5 ml  kg-1  min-1
Arm ergometry
3.0 ml/kgm

21. Estimating the Energy Cost of Leg Ergometry
Gross VO2
Net VO2
Resting VO2
Loaded cycling
Unloaded cycling
3.5 ml  kg-1  min-1
This equation calculates VO2 in the units of ml  kg-1  min-1

22. Estimating the Energy Cost of Leg Ergometry
Gross VO2
Net VO2
Resting VO2
(1.8)(kgm*)(kg body wt)
3.5 ml  kg-1  min-1
3.5 ml kg-1  min-1
*kgm = (kg at flywheel)(rev/min)(m/rev)
(f) = step frequency in steps/min; (h) = grade expressed as a fraction

23. Estimating the Energy Cost of Arm Ergometry
Gross VO2
Net VO2
Resting VO2
Loaded cycling
3.5 ml  kg-1  min-1
This equation calculates VO2 in the units of ml  kg-1 min-1

24. Estimating the Energy Cost of Arm Ergometry
Gross VO2
Net VO2
Resting VO2
(3.0)(kgm*)(kg body wt)
3.5 ml  kg-1  min-1
*kgm = (kg at flywheel)(rev/min)(m/rev)
(f) = step frequency in steps/min; (h) = grade expressed as a fraction