Exercise physiology - Mechanical Efficiency during running

Could someone please discuss the practical implications for testing and knowing that someone has significantly lower economy of movement (mechanical efficiency) during running than they should?

[This is the second time I have posted this problem because I did not understand the first response which stated ATP. But what does it mean by "practical implacations for tesing. Does 'lower economy of movement during running imply incorrect form, wasted energy, bad shoes... I am having a hard time understanding this concept.]