Yes, the total load is sort of what I was getting at not that training in the heat would help acclimatize to altitude. I’m not sure I stated my question very well though (or that I will do better now). For instance I carry a 35lb backpack at 90F at sea level and my heart rate would be hire than if it were 50F on the same route and speed. So I guess I was wondering if heat drives the total heart rate load in a similar way to altitude by raising it higher than a less stressful environment. So would the HR load be similar under these two totally different circumstances due to environmental stress? Hopefully, this makes sense although I may be off down a dirt road as well. 🙂