coach_izzy:
Please define fitness before you keep going further. The statement refers to what was mentioned about 20 minutes being sufficient at the levels being presented, which will do nothing more than elevate core temperature and provide very little benefits in the long term. Once again, take the time to read properly as well as all that's implied.
Fitness in the most general sense is being suitably trained to accomplish your goal. If your goal is powerlifting, being able to run a marathon does not make you "fit" for the task at hand, and vice-versa. "Fitness" in the context of this discussion, in my mind is general health and weight loss.
coach_izzy:
And since you seem to know so much about lactate treshold training, please elaborate what it is and how is not applicable to conditioning. Catherine and Countryboy want to know and I'm sure you have great knolwedge of what it is since you made such a witty analogy... Care to give it a shot?
In general terms, lactate threshold training is training at or slightly above lactate threshold pace (running) or power (cycling). Due to the high intensity of the work period, an LT workout is usually done as an interval set with a predefined number of work periods and recovery periods. LT is generally defined as the pace/power which is sustainable for 60 minutes in a race situation. A good analogy would be the pace at which you can run a 10K at. LT is specifically defined as the point at which blood lactate concentration in the bloodstream rises above some baseline level though this requires a blood analyzer to determine. The purpose of LT training is to increase LT power or pace. If you have a specific goal of running a faster 10K or marathon, or riding a faster time trial, LT training is an integral part of training. If you have a goal of losing fat or increasing lean body mass, LT training is probably not the right tool to use.
Now, with all of that said, I think that this thread has needlessly overcomplicated matters. In my mind, there are a few key principles that will serve people very well if the goal is weight loss and general health.
1) When the goal is fat loss the name of the game is raw calorie burn. If you can burn more calories than you eat, you'll lose weight.
2) Every exercise you do has a "recovery cost", that is, your body has to work to recover from the work you did.
3) The key variables when talking about exercise are intensity, duration, and frequency.
4) A low intensity/high duration exercise is easier for your body to recover from than a high intensity/low duration exercise.
5) Faster recovery means that you can have more quality workouts per week, thus increasing your overall calorie burn.
Can you lose weight, by working out for 20 minutes, 3 times per week? Sure. You just need to adjust your dietary plan to balance calorie intake with calorie burn. My main issues with LT training for weight loss are:
1) LT training is a high stressor, thereby increasing the risk of injury if the body doesn't have a suitable level of base fitness.
2) The recovery cost of LT training is high so this is not an efficient use of the body's recovery resources. This is a very specific form of training that has a high cost and risk associated with it, and no clearly discernable benefits to someone looking to lose weight. To put it in simple terms, let's compare two workouts. I can either go out and run 6 miles at a 10 minute pace, or I can run 2 miles at a 6 minute pace. I will definitely be more sore from the latter workout. I will burn more calories from the first one. I will also be able to do the first one again the next day (assuming I've been running for a little while and this isn't my first workout), while it will probably take me several days of recovery before I can go out and run another 2 miles at a 6 minute pace. Which plan do you think is better for weight loss (the context of this discussion).
Now if the discussion is not strictly weight loss and you want to talk about how to run a faster 10K or triathlon, the context changes and my answers will change.