True Fitness CS4 Owner's Manual page 51

Appendix C
True treadmills use the calorie expenditure formula as
described in Guidelines for Exercise Testing and Prescription
from the American College of Sports Medicine. This is the
most widely accepted formula for running and walking.
The ACSM guide says that running burns calories twice as fast
as walking, e.g., a 150-pound person jogging at 5 mph requires
548 calories per hour, while walking at 5 mph requires 274 per
hour.
(Other respected researchers such as David Costill think the
ACSM overstates the energy difference between running and
walking. Costill believes running requires 60% more energy
than walking, not 100% as calculated by the ACSM. Using the
same example, Costill's calculations result in 496 cal/hour for
running 5 mph, with 313 cal/hour for walking 5 mph.)
One potential source of calorie estimate error is that the
treadmill doesn't know if you are running or walking, so it
has to make some assumptions. It assumes you are walking
at 3 mph and slower, and running at 5 mph
and faster. Between those two speeds, the
treadmill combines the walking and running
formulas to make its best guess.
Variations in human exercise efficiency
are another potential source of error, with
differences of plus or minus 20% common in
the population.
54
CS Treadmill Owner's Guide
A Note About
Calorie
Expenditure
Calculations