Most of these workouts are in the overtraining zone. If we notice, a lot of people talk of results of injuries, bad races and being burnt out.
The toughest workout and the best workout are never the same. In fact my best workouts are when I cut it short by maybe 10 to 25% because I am hitting amazing times. For example if I had 10 400's with 1 min rest, and I am hitting 58 instead of 60 all the way through, I will definitely do no more than 8 400's. Knowing when to cut is always a good idea.
I remember one year in college, I spent a week in Gainesville before Florida relays. The Tuesday I ran a 20 min tempo in the morning at 5 min pace. The afternoon I did 6x300 at 36 point with 2 mins recovery feeling really amazing. At that point I should have taken it easy the rest of the week. But the Wednesday morning I ended up doing a balls to the wall 12 mile run. I ran the worst 800m leg I ever ran on a sprint medley that friday at Florida Relays.
In college, more runners have been lost to overtraining than undertraining. The freshman year "swim or sink" mentality of most coaches destroys a lot of talent. Add to that the overracing, especially running cross-country, indoor and outdoor, and we find the reason so much talent is lost.
The hardest workout we did in college was once a year, always the Sat before the Patriot's day in New England. 2x800, 4x400, and one 1200. the 800's were below two mins, the 400's were typically 56 and the 1200 below 3.10. the recovery after each repeat was 400 jog in just over 2 mins throughout the entire workout. I never ever finished the 1200. And I would surely beat guys who finished the 1200 in the rest of the races for the season. I guess my body knew that the 1200 was just bullshit for me.
Sometimes it really has to do with how we are wired. We used to do a workout indoor that most of the guys hated and I loved. It was 25x200 with 100m jog rest. we would start at 30 and get down to 28's. In the last five, I would typically be on my own while my teammates cursed me as I started running 27's while they struggled at 28's and 29's. I would even run the last one at 26 point.