What causes the extreme bodily distress after all out efforts in short races?

The following is based on a brief discussion on the Slowtwitch blog in March of 2015. Here is the series of comments that started this. The discussion was about the value of doing an all-out 1-hour cycling test at max effort, often called a FTP test. Such an effort is often close to the time needed to complete a 40K Time Trial.

• First comment - I translate that as 'your time in a 40k TT is a good predictor of your time in a 40k TT'... which brought this response from someone else


• Next comment - Well it is a good predictor of your performance in everything from a 15 minute to 5 hours TT really...to which we responded


• Our comment - So is a 4-5 minute test estimating the V4 (P4 for cycling.) Two 4-5 minute tests are even more accurate and requires no motivation or effort to maintain a specific effort nor does it interfere with whatever training is planned...This response brought a response that appeared to not understand what we were trying to say but is instructive


• Next comment - Depends on how you test. As a former collegiate 1500m runner and current track 3K pursuit rider, I can tell you that a truly all-out 4:00 is devastatingly hard. Mentally and physically. And certainly interferes with training.
  
  First - We should have said "4-5 minute sub-maximal test." We wrongly assumed that readers would know that a 4-5 minute all-out effort is not relevant in estimating V4 or P4. We recommend one effort below the 4 mmol/l level and then one above. These are not overly stressful. For example, in swimming the first effort is about 25-30 seconds slower than one's fastest time for 400m.
  
  I am sure that a swimmer would prefer one 4-5 minute test that is 25 seconds less than his fastest time to swimming a T30, which is 30 minutes all-out. And most cyclists would prefer a 4-5 minute test where the pace is slower than an all-out 60 minute effort. The runner would use a 1600m or 2000m run on a track that is about 20-25 seconds slower than his or her fastest time. These single efforts can be used to predict the V4 or P4 from which training levels can be prescribed. Two sub-maximal efforts are more precise.
  
  Second - What causes the "devastatingly hard" feeling both mentally and physically by an all-out effort at this relatively short distance? We made the following response to this commenter.


• Our comment - One of most grueling or all races is a 2000 m rowing race (around 6 minutes). We have seen instances where the rowers had to be physically lifted out of the boat after the race because they couldn't move. It is extremely anaerobic often generating way over 20 mmol/l of lactate.
  
  To which we received the following criticism:
  
  Next comment - Any effort more than ~70 s in duration is predominantly aerobically fueled. During a ~6 min effort, >90% of the ATP will be generated aerobically.
  
  Of course we know that rowing events are primarily aerobic and frequently talk of the importance of the aerobic component to any race greater than 40 seconds. For example, the 100 m freestyle in swimming is a race with a large aerobic component.
  
  
• The commenter was actually technically incorrect, as a 2000 m rowing race is 80-85% aerobic depending upon the type of athlete. Hardly anything to quibble over but the commenter missed the essential point of the discussion. Which is why an all-out effort over 4 minutes is so devastatingly hard. It is not the aerobic system that is causing this feeling. It is using the anaerobic system to a high level that causes the athlete to feel completely exhausted.
  
  The following example is illustrative. We once attended an Ironman race in Europe where some of the top European triathletes were competing. The winner won in 8:04 hrs. This is a very fast time and presumably an all-out effort. As the winner came into the finish line, he was all smiles and high-fiving all the spectators along the way. He finished and immediately went to the television announcer and started discussing the race. He wasn’t even breathing hard.
  
  Now why are athletes with all-out efforts at 4-6 minutes devastated after the effort but an athlete after an 8-hour all-out effort is not even fazed? The answer is that the anaerobic system is heavily involved in the shorter events and not as heavily involved in the 8-hour event. So the nitpicker misses the point that the anaerobic system severely affects athletes at events of this duration.
  
  But the real question is why would anyone want to spend 60 minutes at an all-out effort to measure something as a basis for training when two sub-maximal efforts at 4-6 minutes will provide better information? Especially if a short all-out effort of 60 seconds or less is added to the testing.