These last few weeks have been really interesting from a training perspective. I have experienced true "redlining" of my abilities in many of my workouts.
This has really shown up in my track workouts at trying to maintain a super high pace for a given distance, whether it's 800 meters or distance tempo workouts of up to 4000m in length. It also showed up last weekend for the Long Beach Half Marathon where I could feel and, later, see my effort and heart rate rise to super high levels for the entire race.
It's a weird experience being in a redlined state for a long time. At points during my track intervals, I have gotten to the point of almost feeling dizzy and passing out, and then backing off a tad to maintain as high a pace as possible. In the longer distance tempo workouts, I have focused on leg turnover and, in maintaining a certain leg turnover rate, my HR jumps to a really high level.
It's good practice. Pushing my tolerance to higher thresholds allows me to keep performance high for longer periods of time and maxes my output.
It's potentially bad in that one of these days I may push over some physical limit and pass out during a race. That would definitely NOT be good.
Afterwards, I find that my body is a bit slower in recovering after these workouts. I have maintained my effort so close to my lactate threshold for so long that I feel it in my lungs and body for days afterwards.
I don't know of any other way of training to push my performance higher; I need to continually push my body to the edge to eke out that last bit of speed. As long as I don't push over the edge, it seems that my body recovers and learns so that next time I improve and it's not so bad.
I look forward to seeing what happens at NYC in two weeks when I will maintain this level of output at marathon distance.