Rule-of-Thumb: 2 sec/mile/pound

Last time we looked at a rule-of-thumb for energy used in running.  Today we’ll look at

another rule-of -thumb for the effect of runner weight on pace.  There is a fair amount of wild speculation, rigorous study, anecdotal experience, and intuitive assertion about this topic, but a lot of conclusions seem to center around a time penalty of 1-4 seconds per mile per pound of body weight.  We’ll look at that range in terms of energy use.

This figure shows the time penalty based only on mechanical energy use as a function of power output, for several vertical displacements and stride lengths.  The green band illustrates a rule-of-thumb range of 1.5-3.5 seconds per mile per pound of body weight.

The rule-of-thumb, while rough, does appear to be in the ballpark for many realistic situations.
Remember that our assumptions in making this figure account only for the energy used in each upward vertical displacement and neglect any energy recovery during the downward motion, and also neglect any energy use for horizontal motion.  It seems unlikely that there is much energy recovery from the downward motion, but the horizontal motion, while not requiring any mechanical energy output, could certainly require muscular output which would affect the time penalty.

 I’d like to acknowledge and thank reader KAB for suggesting this topic.