The age-old "talk test" to determine the appropriate level at which to exercise should be reconsidered. You can't comfortably complete a sentence once lactate begins to accumulate in your blood, but that doesn't mean you can't keep exercising. In fact, exercise duration is only significantly limited when the blood lactate increase is inexorable.
The aerobic system is still the predominant energy transfer process in effect when you transcend the lactate threshold. The increased presence of lactate in the blood simply means that anaerobic sources are also chipping in. But the key determinant of exercise tolerance is whether lactate levels eventually plateau. If they do, you can continue to work for a prolonged period. And even though it might not be the most comfortable experience, aerobic work done at this level is associated with a greater payback.
There are two general benefits that you'll gain from doing aerobic exercise on a regular basis. Your cardiovascular system will improve its function over time and you'll use energy during each session that will go a long way toward establishing the negative energy balance you need to drop body fat. Working at higher intensities overloads the circulatory system to a greater extent and forces it to adapt to a higher level. And energy use is a function of intensity and time, so if you want to use a lot without spending half your waking hours working out, a higher intensity is the way to go. But if the threshold identified by the talk test doesn't identify the upper limit of the sustainable exercise domain, what does?
Research has definitively shown that the supra-lactate threshold region of the metabolic spectrum can be divided into two distinct regions. The dividing line that separates these domains is the asymptote of the hyperbolic power-time curve. That means there is a cutoff point below which you can maintain workloads for prolonged duration. Physiologically, work rates above this point will be characterized by different precipitants of fatigue.
The power-time asymptote is intimately related to the maximal lactate steady state, which is the metabolic demand above which anaerobic sources play a considerable role and blood lactate continues to increase until exhaustion. In fact, the ever-rising lactate at these intensities might actually be what causes you to stop. But the key thing to remember is that if you don't surpass this level, blood lactate will be elevated, but stable, so you'll fail the talk test, but be able to exercise for as long as you need. The workload associated with the power-time asymptote during cycle exercise has been termed the critical power. If running is your preference, it's called the critical velocity. But either way, it indicates the intensity at which you should exercise if you want the biggest bang for the time you invest. And it's also the level that dictates the pace an athlete should maintain throughout a mid-range endurance event.
Unlike the lactate threshold, there is no easy way like talking to identify the maximal lactate steady state or critical power. The former requires monitoring blood lactate levels as a number of discrete workloads are imposed to determine the highest one that doesn't cause a continued rise. The latter requires working against a number of different workloads above the critical power to determine duration to exhaustion at each. Plotting these points will allow the individual's hyperbolic power-time relationship to be quantified, thereby providing the information needed to identify the point directly below it.
For athletes whose training and race pace must be precisely determined, lab tests like the aforementioned provide important information. For the average exerciser, roughly determining the critical power/velocity by trial and error is a good plan of attack. Start your cardio at a slow pace, gradually increasing for the first five minutes to give your aerobic energy system time to adapt to the increased demand. If you don't, you will experience signs that the workload is not sustainable, even though it is. Once this warm-up is complete, keep increasing pace gradually until you find a level that you cannot sustain and note what that workload is.
Back off a bit and complete your exercise session. Next time you exercise, ascend to a level a little less demanding and see what happens. Eventually, you'll find your highest sustainable pace, at least given your current level of conditioning. Some exercisers employ interval training where they intersperse work periods above critical power with recovery intervals below. This is really tough and could provide the competitive advantage an athlete needs, but for the average exerciser looking to burn calories, the extra energy you'll use during your intervals above will probably be more than offset by what you'll sacrifice when recovering below.
The shortest distance between two points is a straight line and the most direct route to maximum energy use and central circulatory overload is exercise at the critical power. Forget the talk test and increase your cardio intensity today!
Fred Dimenna, a Certified Strength and Conditioning Specialist and lifestyle and Weight Management Consultant is a two-time Natural Mr. United States and a WNBF drug-free professional bodybuilder. Visit him at www.freddimenna.com or email him: firstname.lastname@example.org