Ekso Bionics Holdings Inc (EKSO)

[Rhetorical]

From an Ekso Bionics Patent

Look at the physics of being efficient for yourself:

"(M TRUNK L 2+I){umlaut over (ß)}1-(LM TRUNK +RM L)g Sin(ß1+a)+T F

wherein:
M TRUNK is a mass of the exoskeleton trunk and any attached load;

ML is a mass of the respective first and second leg support in the stance phase;

I is moment of inertia of the respective first and second leg support in the stance phase;

L is a length of the respective first and second leg support in the stance phase;

R is a distance between a center of mass of the respective first and second leg support in the stance phase and a rotational point;
g is force due to gravity;

ß1 is an angle between a support surface and the normal line of force on the exoskeleton trunk from the person's upper body;
a is a ground slope defined by an angle between a support surface and a horizontal plane;

and TF is a frictional torque opposing the motion of the leg support relative to the exoskeleton trunk."

http://www.google.com/patents/US8945028