Dead legs and a track session

RUN: 8.1 miles in 70 mins
BIKE: 22.1 miles in 80 mins, 1x30 and 1x20 mins at 115-120bpm

As I was preparing for the run, I started wondering at what point I had to reel myself in and rest. A tendon or something in the bottom of my right foot hurt, my right "stablizing" muscles hurt, and my legs were lacking zip. At what point does the balance tip into injury and burnout from improvement and healthy stress? I'm not yet there, apparently.

The session was 2 sets of a descending distance ladder, to be done at 88-92% effort, with 200 rest in between. No HR data today, DH was in the bathroom where the HRM was!:
1000: 6:46m/m 4:48 0.71mi
600: 6:36m/m 2:46 0.42mi
800: 6:26m/m 3:38 0.56mi
200: 6:18m/m 0:50 0.13mi
The second set of intervals should be the same if not faster, after an 800 rest:
1000: 6:17m/m 4:30 0.72mi
600: 6:27m/m 2:41 0.42mi
800: 7:01 m/m 3:36 0.51mi*
200: 6:31m/m 0:54 0.12mi*

I knew in the warm-up that my legs were like dead weight. I took an extra lap to see if some straight-section spin-ups would help...not really. Again I started wondering at what point I take this all too far? What if I stumble on the track and fall? What if an ankle or knee mis-steps and gets torn up? I'm not that far in real fatigue just yet, I guess.

The first 1000 seemed flat and uninspired, but I did fairly well with it. The 200 rest intervals gave me just enough time to recover. The difference between 1000 and 600 seemed huge, and heck an 800 was only 200 more than the 600 I just did, and only a 200? This was a pleasant mental workout as well.

IT joined me starting around the 1st set 600 or 800. He was running faster so I had a rabbit to catch. That might explain the improved times on the subsequent intervals :)

*I ran the last 2 intervals in the counter-clockwise direction, being more careful to stop the garmin at the right point. I think in previous sessions I was stopping it too early and thus making the data look messed up.

In the end I was wiped out, drenched in sweat, and hungry. But I still had a bike ride! So a slow run up the hill to home, hop on the trainer to get the steady intervals, and get in what I can of a 2x30min 75% session. I didn't get it all, but I got a majority.