So, I had my follow-up heart scans yesterday after nearly 7 weeks of no recorded avg HR over ~110bpm (usually <105bpm) and no run over 60mins. I've been averaging about 40k per week for the period with pace dropping from 4:45/km down to 6:00/km (or slower) most recently.
The good news is that the volume of my left atrium has decreased from 46mL/m2 to 40mL/m2 which means I'm at a much lower risk of atrial fibrillation, and shows that the size of the atrium is definitely an adaptation to my training (vs. being some other medical condition). The not so good news is that it's still classified as 'severely abnormal
', although <40mL/m2 would only be 'moderately abnormal
' so I'm not far off
Now... the really interesting thing is what happened when I went for a run today and pushed a little. After the usual 100-110bpm start I tried 2x 2k pretty hard (roughly 5k 'all out' effort
) and I recorded a new highest Max HR of 180bpm! In the second 2k I was at 175+ for well over 5 mins.
Consider that in 10 years of using HR monitors I've only once
seen a HR over 175, and that was just for a few seconds at the top of a hill in a race (and with optical HR which makes it debatable). At the end of the marathon in Oct I was wearing a strap and hit a Max of 172 for the last 5 seconds crossing the line. In the 15:54 5k in Sept I never went over 170bpm.
It's probably too early to say whether the ability to reach and sustain higher heart rates is related to the smaller atrial volume but it seems likely. If it is indeed the case then I'm wondering if I can develop this "new type of fitness
" where I'm able to sustain higher heart rates, and therefore run faster with a lower atrial volume and lower risk of AFib
That's the hypothesis anyway...
The other interesting thing is that the 2ks today really weren't that slow... 6:55 and 6:38, despite literally nothing more than a jog in 7 weeks!! That tells me I've probably still got some de-conditioning to go before I reach rock-bottom fitness, so hopefully I can get the atrium even smaller.
That said - the plan now is to take another 6 weeks of very
light training (mostly 100-110bpm) to see if I can bring the atrium down to the moderate range.
After that I'm hoping I can adopt a new training style where I mostly do super low heart rate (although still get decent mileage in so the muscles/bones etc. are strong) and then supplement this with sessions of v. high heart rate (for short periods of time) (e.g. the 2k and 1k's).
Will keep you posted...