So this will be my third and final post on this subject. I too had this spike problem since I’ve owned my Apple Watch. Two different watches, same annoying problem. I have been determined to figure out the issue, and report back on my findings. Please read my other posts for background info, but suffice it to say I have been to doctors, employed many “add on” apps, and am convinced these spikes (at least for me) were not real. The breakthrough was using an app callled FITIV Pulse, which allowed me to watch my heart rate real time on my IPHONE while I exercise. When I caught a spike, I used the an alternative method to check my pulse rate (like the exercise machine monitor, for instance). In all cases, it showed “normal” with the alternate method while my watch read super high heart rates. Frustrating. So for me, I finally found the fix. I am embarrassed to say how simple it was. What I have done, as of late, is to tighten my watch band to the “slightly” beyond comfort tightness....where when I attach the band - it is very tight, to the point it is difficult to get the strap through the slot. It takes some pushing to get it through the slot (the top of the band) to slide it underneath. It is uncomforable for the first few minutes (how tight the band is), but after I get used to it ( please note it is not so tight my hand goes numb!)...but a bit more than snug. Since I have done that, I have seen NO spikes. None. This is after seeing spikes nearly once a day for at least a year, when my watch was only “snug”, not “tight” around my wrist. It completely eliminated the spikes. Another mystery I solved was with other apps (like “Heart Watch”) showing rings completed where the Apple Watch rings are not complete. I realized that these apps are only mimicking the watch rings, and tend to give you FULL exercise minute credit no matter what the intesity. I did an experiment where I turned on my watch for a walk, started the exercise mode, but walked very slowly. As expected, my heart rate was low, and Apple Watch did not give me full credit for the minutes walked. It is obvious the watch is linked to intensity and heart rate, not just the “act” of exercising. The Heart Watch APP, on the other hand, with the same slow walk - gave me full credit. It is similar to the “other” category for exercise with Applewatch, where it gives you full credit no matter what the intesity of the workout. As I get more fit, I notice it is harder and harder to get the credit with Applewatch, as my heart rate is better/lower. My last comment addresses those who have just quit wearing their watch because of the spikes....I can only say this. I am now on day 288 in a row of at least 60 minutes or more of exercise, with 3 rings closed every day. I have never done anything 288 days in a row except eat bad. I travel 3-4 days a week for work, and find myself walking up and down the Atlanta airport concourse tunnel to complete my rings...anything to get the exercise in. It started with a challenge from my daughter for 30 days...she is now at 289 days in a row. Now my entire family is on the challenge. All 3 of my daughters, wife, and son in law. They are at the 50 day mark. I love this watch, despite how hard it was to figure out this annoying spike issue and lack of credit for exercise minutes. For me it provided the inspiration and family support I needed to finally commit to exercising...maybe it is sad it took something like this, but it is working for us. I know I will open myself up to critisism for the “solution”....and cannot say it will work for you....only that maybe this will help you as well, solve this annoying issue, and only wanted to share some of the things I have figured out after a year of working on this issue. I am not promoting the watch or any of the apps I mentioned...just sharing how I used them to finally get rid of these issues.