I just read the "Black Hole" article, and did some testing, and am now totally confused. In one section it defines the black hole as 75-80% of max hr. For me (173 max, last I checked), that's 130 - 138 bpm. I then did the TT test, which yielded and ave of 153 bpm; adding 6% (9) gives a range of 153 - 162 bpm! HUH?!?!?! How in the heck can there be nearly 25 bpm difference in the results for the same zone?! Was there some kind of typo in the article? Or did I do something wrong? (I didn't think to try the "talk test," but there is absolutely no way I can complete a sentence at 153 bpm . . . heck, I'm breathing so freaking hard at that point, I don't think I could utter TWO words!)