For this study to be valid, obviously you need a lot of controls that don't exist or a HUGE group of people to test it on. Either way you're not getting valid results. In the first case, you're not able to control how fast people walk… period. In the second case, the data becomes more and more generalized to get the results leaving many individuals' compositions and techniques truly untested (the study may not apply to everyone).
It would take a 10 page paper for me to fully explain why this study isn't meant to help you! It isn't valid and shouldn't be used by average joe to confirm or attest to anything. Most likely it will be used to progress future studies that properly test these sorts of things providing much more valid information than basically what we already know and probably to sell some sweet cardio poles to overweight americans. Gotta start somewhere right?
As a mechanical engineer I would have to build a very complex force/balance system to actually determine if trekking poles expend more energy. Then I would have the impossible task of building a biomechanical mock up that adequately placed this information into context. Believe it or not, we do not have the $$$ to just test anything we want, especially when there is no benefit to the results. Hence the biased results of this publication, affording them future funding from bodies of the medical/athletic persuasion.
Maybe telling people poles don't expend pointless amounts of energy would sell a few more to hikers each year. Telling the opposite to every overweight desperate American would sell thousands of sticks. This kind of research is biased more often than not unfortunately. Just look at the "8×8" or many other studies of the incredible edible egg. The human body is just far to complex for us to understand with limited funding, and the funding stops when the research starts to pay, not when it is the truth or extrapolated into data that can actually help most individuals.
Sorry to be "that guy". I'll sit quietly in my corner with my foil hat on now. j/k I'm just so tired of all this hoo haaa and what not being used to "prove" things.