A question has arisen on a professional nutrition email discussion list about
the relative efficiency of energy use during running compared to walking.

By way of background, the data in Ainsworth et al (1999) and Ainsworth et al
(2000) indicate that:

Walking at 2 mph (3.2 kph) has a MET equivalent of 2.5.
For 3 mph (4.8 kph) , the MET equivalent is 3.5.
For 3.5 mph (5.6 kph), the MET equivalent is 4.0.
For 5 mph (8 kph), the MET equivalent is 8.0.

If you graph these, the curve for rate of energy expenditure against speed is
approximately linear at least up to 5.6 kph. Somewhere between 5.6 kph and 8 kph
there appears to be an inflection point and energy expenditure then increases at
a greater rate than speed.

Also from the references cited, walking at 8 kph involves the same energy cost
as running at 8 kph (8 METs in each case).

Is it reasonable to assume that below ~8 kph walking is more energy efficient
than running for most people, while above ~8 kph running is generally the more
economical gait?

If so, does this also apply to competitive walkers, or does their technique mean
that the 'crossover point' (at which running economy is greater than walking
economy) occurs at a higher speed?

References

Ainsworth BE et al (1993). Compendium of Physical Activities: classification
of energy costs of human physical activities. Med. Sci. Sports Exerc. 25(1):
71-80.

Ainsworth BE et al (2000). Compendium of Physical Activities: an update of
activity codes and MET intensities. Med. Sci. Sports Exerc. 32(9):
S498-S516.


Chris Forbes-Ewan

Defence Scientist (Nutrition) S&T5
Defence Nutrition
DSTO-Scottsdale
PO Box 147
SCOTTSDALE Tas 7260
AUSTRALIA

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