Have been training for some months below lab tested aet of 127 bpm. On my last two workouts my heart rate climbed to 141 bpm. At that heart rate I was completely comfortable. I could speak in complete sentences and was breathing normally. Caveat it was 100 degrees Fahrenheit with a heat index of 107. Is it possible, before I test, that my new aet is above 140 bpm or is it heat related ? Thanks for any opinions.