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Fig. 1. Simplified view of the forces acting on a runner. The subject is
accelerating forward while running on flat terrain (A) or running uphill at
constant speed (B). The subject's body mass is assumed to be located at the
centre of mass (COM); af=forward acceleration;
g=acceleration of gravity;
g'=(af2+g2)0.5
is the acceleration resulting from the vectorial sum of af
plus g; T=terrain; H=horizontal;
(=arctan
g/af) is the angle between runner's body and T; the
angle between T and H is
'=90
. (Modified from
di Prampero et al., 2002.)