Having read an article on MDA about all the benefits of walking or other low-level aerobic activity, I noticed there wasn't a mention of anything directly related to fitness. Sure, walking helps regulate the metabolism, reduce inflammation, reduces stress, and tones muscles and joints...all good stuff. But for a while now, I have been walking at an intensity to keep my heart rate at the top of Mark's recommended range of 55-75% of max. I'm beginning to wonder if there is any real benefit to being there as opposed to the lower end of the range. I had assumed that the higher my heart rate, the more improvement I'll see in my lung power, endurance, and other fitness measurements. I probably also assumed that I was burning more fat at 75% vs 55%.

I'm asking about this because to achieve 75% of my max, there is no steady pace I can move outside. I have to go to a treadmill and put it at the right incline. The boredom is starting to get to me. I would rather be outside and relax. But outside, if I jog continuously, my heart rate gets too high. If I walk continuously, my heart rate never gets high enough. So I'd like to know if I really should be at the upper level of the heart rate range, or if I'd be good with just a 2 mile or so casual walk every day (with little regard to my heart rate). If it matters, I do engage additional activity in the form of weekly sprints and 3-5 days/week of strength training.