Here is what I mean - Over the past 2 weeks, my HR is considerably lower and my calories burnt are way down. Now, I have not turned into an elite endurance athlete where the readings could be justified. I play tennis and my HR will vary. For the past 6 weeks I average close to 1000 calories per 1.5-2 hour session. HR in the fat burning to cardio zone, roughly 65-85% for most of the sessions. The past coupe weeks I am only registering close to 600 calories and my HR is consistently is the warm up zone, 60% of max HR. Any idea why the sudden change? I have used the stock app, and two different third party apps and they all are doing the same thing.