I’m sure Scott will jump in a flush your question out further. However, here are a couple of thoughts based on what I have heard on these forums in the past and my own experience.
– The 110 HR average is right on the line of the 55% of Max HR you’re referring too. Thus, the answer will likely be very athlete specific (training goals, training history, etc.)
– Average HR for a workout is only one piece of information. In a longer workout (1 – 6 hours) we can hit a range of heart rates, and average HR alone won’t tell the whole story.
– Training Goals we’ll be a factor. How important is it for an athlete to hike with his/her friend once and awhile? What are athletes goals for training (Become a world champion, just improve by some metrict, etc.)?
– Training history will be a big factor in this discussion as well.
Here is an example: When I first started training, I could barely hold down a “running” pace with an Avg HR in the 135 range on flat terrain. After several years of training, I can hit much faster running paces at a HR of 120 on flat terrain. Four years ago if had done an Aerobic Base run at 120 HR I would have been walking really slowly and not getting much of a workout . Now, it’s actually a decent workout, so much so, that trying to run on flat terrain at a HR of 146 (AeT) would be a semi-hard workout for me. As such, I try to stay on the trail with hills most of the time. Some days when I “feel strong” I’ll run with an Avg HR in the 140 range. On days I feel fatigued, I run with an average HR in the 120 range. Compare that to my first year where I always ran around a 135 HR and that worked just fine.