Hi everyone Really glad to find some discussion on this subject. I have started using a heart rate monitor in the past few days and am finding it intriguing. I didn't spend all that much on mine (from Amazon) but it has the ECG-accurate chest strap (as someone else said, performance is improved by adding conductive gel). Here are my observations so far: My initial excitement at having something so concrete and immediate that I could follow was short-lived as it quickly became apparent that my limits were much narrower than I had ever imagined. I thought I was being ultra-cautious and taking it really easy with rest and avoiding doing anything too exerting. Turns out I was wrong. This led to an initial panic and bleak mood centred around worrying that I was going to have to be bed-bound and laying flat for pretty much my whole day and night. This has now lifted as I have learned how I can avoid huge spikes in heart rate and take rest as soon as I need to. It's early days but I am becoming more and more confident that this will be a huge benefit for me in balancing activity with rest. The lady who got me interested in this idea has been using the formula she found on the CFIDS website of 220 minus Age then multiply that total by 0.6. This means that, for me at 37, I have a threshold of 109. I'm finding this to be a good indicator of when I need to get flat or at least sit down. I decided to switch the alarm off as I found it was anxiety-inducing for me. The downside is that I have to keep checking my watch when I'm on my feet but I'm finding that easy enough to maintain. Even if I don't end up wearing this forever, I think I am quickly picking up some really great indications of where my limits are and what activities or movements in particular are causing my heart rate to elevate excessively. The caveat I'd like to add is that it requires discipline to not ignore the heart rate and just push through anyway. It's always very temping to 'just finish what I'm doing' but it's counter-productive. So, now I rest halfway up the stairs, avoid bending down or stretching or putting my hands above my head as much as I can. I also have accepted the benefit of peeing sitting down, lol. All this can make daily life tedious and boring so the discipline required shouldn't be under-estimated. Finally, my 'mentor' in this gave me a great observation based on her experiences. We are told to eat little and often and this would seem to be backed up by our experiences with the heart rate monitor. Eating a large meal makes it much harder to avoid elevated heart rate on exertion afterwards as so much energy is being put into digestion. So, this may also help my waistline, lol.