Hi folks, i've set my max heart rate at 187 as thats been my max heart rate over the last six months. Now, i've just started with the garmin 225 and the last couple of times i've been out i've noticed that i've reached my max but not gone beyond it even though i was pushing hard. Is this some sort of safety feature and if so how do i measure my new max heart rate as i continue to train if the device won't record above the pre set max?