OP here. I don't race. I don't even train per se. I just ride a lot of hilly terrain and look at what my bike computer spits out after a ride. After the last couple of long-ish climbs (for me anyway) - a 2000 ft in 10 miles during a 30 mile ride and a 3000 ft climb in 15 during a 50 - I noticed that what I now realize is my VAM was pretty constant despite the fact that the grade varied between 2 and 15% in both climbs. I'm not at all strategic about my energy use. I'm not thinking about my next climb, but only about maintaining a level of effort that can sustain indefinitely (or at least for multiple hours). For me that means a heart rate in zone 3 or 4 and I guess I just unconsciously calibrate my effort to that level regardless of how steep the climb. From the discussion of VAM in this thread and its use as a proxy for power I guess that just means I.m operating at a consistent HRM and power output regardless of terrain. None of this analysis is necessary, but it gives me some insight into my style of riding (and exercise in general). Thanks.