A great run today

This morning I was scheduled to run 60 minutes, including two 20-minute tempo intervals at heart rate zone 4. What does this mean? My heart rate zone 4 is anywhere between 169 and 179 beats per minute, which I measure with my Polar heart rate monitor. I went for my run this morning after waking up with a BG of about 90 (yay!). I was a little concerned that I might drop, so I ate half of a banana, which brought me up to about 110 by the time I started running. After 16 minutes of warmup, I began the first 20-minute tempo interval. I was feeling the slightest bit low but assumed I wasn't low for two reasons: I ate the banana (well, half) and I rarely drop low when I exercise first thing in the morning (before taking any boluses). Nonetheless, I decided to take some preventive action and ate a ClifShot a few minutes in, and turned my basal down 40% for an hour. (I had a really horrible low 2 weeks ago that took me 20 minutes to recover from during a similar run; while waiting, there was a freakish hail storm and I was stuck there under a big tree, trying to stay dry while obsessively checking my BG every 45 seconds. This run was during the lunch hour--not early morning like today--so I wasn't terribly concerned about a repeat event.) Anyway, I tested after the first interval and I was 174, which was acceptable. I usually like to let the BG drift up a little, just because I hate having lows so much while exercising. Still, I wish I could figure out how to have a BG of 120 all the time while exercising! Is this even remotely possible? The second interval was slightly uphill, which made it a little easier to keep my heart rate up in HR zone 4. My average HR for this interval was 173 or so. Following my run, my BG was about 240 so I took a corrective bolus. I think that it was probably only necessary to reduce my basal for the first half hour, while I was still close to 100, or to not eat the snack. I was in the groove and didn't feel like pulling out my BG meter during the first interval; this would have been the better solution. (Even better would be to have my Dexcom working again. I need to order some additional sensors.)