Agghh the good old 'lactate threshold' debate!
As I own my own metabolic and fitness assessment company specialising in lactate testing this figure does indeed differ from individual. The fitter you are the higher the lactate threshold and in general the longer you can sustain this effort for. I could hold a true lactate threshold for well over 2 hrs if need be. In fact a 75 mile road race last year I was close to or over my lactate threshold for the majority of the 3 hr race!
For an untrained individual lactate threshold could be very low in comparison to a %tage of maximum heart rate (65 - 75% mhr). But in a trained individual their lactate threshold could be alot higher (75 - 90% mhr). So in theory you can work faster in a better trained athlete.
Lactate threshold is simply the point in which your body accumilates lactate but cannot buffer it and get rid of it whilst working at the same level. So keep going and you will soon run out of steam and get slower. You are still aerobic at this point and burning fat when at lactate threshold. The time able to spend above this zone varies with each athlete but a fitter and stronger athlete will be able to 'suffer' more and go for longer.
One day specialist riders in the 'classics' for instance will probably be able to tolerate huge periods of time above this point especially when attacking and in breakaways.
Lactate threshold is the same as anaerobic threshold. It just gets called different things in different countries.
When your body goes into a complete anaerobic state however this is the effrot where your body will shut down reasonably quickly. But again it varies upon individuals and each athlete. Once completely anaerobic (without oxygen) you burn no body fat. Without your body burning any fat it means your body must source all of it's energy from quick release energy systems (glycogen/sugars/carbs).
Now your body only has around 2500-4500 calories to use from glycogen/carbs but nearly 10 times as much from fat (25'000 - 45'000 calories!). So you can see why it is so importnant to metabolise fats better... to raise lactate threshold... to raise your anaerobic state... so you constantly burn fat when execising at almost every heart rate.
This is why Lance Armstrong is so good at long stage racing... he burns fat to approximately 98% of his max heart rate which means he is still aerobic and burning fat! This also means as a result he will recover quicker! Which is why he can go from stage to stage better recovered than most to be able to race better and more fresher!
Obviously this takes alot of practise and training to get to this level... over 6-7 years in fact!
You need to get tested regularly (3 - 4 times a year) to see how your thresholds change to make the training adaptions neccessary to get faster and fitter!
You got it a bit wrong, to start glycogen is a pure aerobic energy source. In addition, we all burn fat to 98% or so of our max heart rate.
"better... to raise lactate threshold... to raise your anaerobic state... so you constantly burn fat when execising at almost every heart rate."
You must mean aerobic efficiency? Lance's advantange is that he is more efficient. A very recent paper documents this.
"J Appl Physiol. 2005 Mar 17; [Epub ahead of print] Related Articles,
Improved muscular efficiency displayed as 'Tour de France' champion
Kinesiology and Health Education, The University of Texas at Austin,
Austin, TX, USA.
This case describes the physiological maturation from ages 21-28 y of
the bicyclist who has now become the six-time consecutive
'Grand-Champion' of the 'Tour de France', at ages 27-32 y. Maximal
oxygen uptake (VO2max) in the trained state remained at approximately 6
l/min, lean body weight remained at approximately 70 kg and maximal
heart rate declined from 207 to 200 beats/min. Blood lactate threshold
was typical of competitive cyclists in that it occurred at 76-85%
VO2max, yet maximal blood lactate concentration was remarkably low in
the trained state. It appears that an 8% improvement in muscular
efficiency and thus power production when cycling at a given VO2 is the
characteristic that improved most as this athlete matured from ages
21-28 y. It is noteworthy that at age 25 y this champion developed
advanced cancer , requiring surgeries and chemotherapy. During the
months leading up to each of his 'Tour de France' victories, he reduced
body weight and body fat by 4-7 kg (i.e.; approximately 7%). Therefore,
over the seven year period, an improvement in muscular efficiency and
reduced body fat contributed equally to a remarkable 18% improvement in
his steady-state power per kg body weight when cycling at a given VO2.
(e.g.; 5 l/min). It is hypothesized that the improved muscular
efficiency probably reflects changes in muscle myosin type stimulated
from years of training intensely for 3-6 h on most days."