One study compared hiking poles of three different weights. and found that muscle activity (electromyography) of the biceps brachii and anterior deltoid increased with increasing pole weight. The anterior deltoid assists in flexion of the shoulder (brining your upper arm from your side to in front of you horizontally) and also is needed to resist gravity and the weight of your arm. With a hiking pole with increasing weight, this muscle should increase in activation. The biceps brachii (or just your biceps) work to flex your elbow, and again will be increasingly activated as more load is placed on the hand as your arm is out in front of you.
Lightweight Leki Poles are nice, but is it worth it?
However, this study found no significant difference in energy expenditure (VO2 consumption) with increasing pole mass. Looking at the paper, they are not clear on what the actual values for VO2 intake were (regardless of whether the differences were significant), so its hard to tell if there still was possibly an increase in energy expenditure (albeit not statistically significant). I'll have to read through it further.
Another paper also somewhat looked at the effect of pole mass and did not find any significant change in energy expenditure.
So it seems that the current research is indicating that pole mass (within realistic levels as found in stores) does not make much of a difference in energy. The mass will, however, increase the loading and activation of a few muscles, although it's not clear whether these levels could be tiresome over the course of a day.
How can upper arm muscle activity increase but not energy expenditure? Well the mechanics are pretty complicated, but it may be simply that those muscles aren't consuming much energy to begin with. Or the heavier poles have some benefit in other manner (natural arm swing frequency?). It's not clear.
For those of you that use poles? What do you think? Certainly lighter poles feel better. But have you noticed an effect on performance with different pole weight?
Link to some discussions