Metabolic Misconceptions: Part 10: The Lactate Threshold
by Fred Dimenna, CSCS

If your goal is to reduce body fat by exercising, the ultimate determinant of how successful you’ll be is how much energy you use in relation to the amount you ingest. If you shift energy balance so that expenditure exceeds intake, you’ll access stored fuel. And if lean mass is spared when this negative energy balance predominates, the stored fuel you tap will be fat. In keeping with this goal, aerobic exercise should be performed with one objective: Using the most energy you possibly can. If you limit yourself by employing methods designed to maximize relative fat use, this objective will be difficult to attain. Working as hard as you can for as long as you can as often as possible is, therefore, paramount.

Understanding how you’ll feel as you transcend the spectrum from minimum (fast asleep) to maximum (working as hard as you can) energy outlay provides a quantification method to determine how hard you are working as you exercise. Armed with this knowledge, identifying specific points along this continuum will allow you to find your ideal pace. There are two particular points as you progress from minimum to maximum effort that you should be able to detect. The lactate threshold is the workload associated with the first sustained increase of lactate in the blood. This is marked by labored breathing (lactate is buffered to carbon dioxide, which stimulates ventilation) and ensuing discomfort in the working musculature. If you establish your aerobic intensity according to the "talk test," you’ll always wind up below this breakpoint because going above it ensures you’ll be gasping for air before any conversation gets off the ground. It is often assumed that exercise above the lactate threshold cannot be sustained for extended periods, but this is not necessarily the case.

Obviously, no activity can be maintained forever, as our time here on earth is finite. However, a theoretical discussion of the ability to sustain work separates activities that can be continued until long-range hurdles (glycogen depletion, for example) create an obstacle versus those that must be truncated in a more immediate sense. A graphic representation of this work-rate/sustainable-time relationship is described by a hyperbolic function.

To visualize this association, picture a graph with a horizontal (x) and vertical (y) axis. Sustainable duration is plotted on the x-axis, with work rate specified on the y. The resulting plots will form a hyperbola (picture a "C" that is tipped to the left so that its ends extend along each axis). This means that at one extreme, the highest work rate you can possibly do can be continued for the shortest period of time, while lesser challenges can’t be maintained for much longer. Once you reach the more dramatic curved portion of the "C," however, every slight reduction in work rate will be accompanied by a relatively large increase in sustainable duration. Eventually, since the curve extends infinitely outward, its asymptote will, theoretically, represent the workload at which you won&Mac226;t encounter short-term barriers to continued performance. This asymptote has been dubbed the critical power (or velocity, if running or swimming are your exercises of choice).

The critical power and lactate threshold are not synonymous: There is, in fact, a zone between the two. Generally speaking, critical power occurs approximately halfway between the lactate threshold and the ultimate ceiling (the workload associated with your highest oxygen consumption or VO2 max). On average, lactate threshold occurs at 60-80% of the max, so the zone between the threshold and critical power is normally large enough to encompass a significant range of workloads. These are challenges that can be maintained for extended periods (30 minutes, for example) if your tolerance for discomfort is up to the task. Working at supra-lactate threshold intensities below or at the critical power is not for beginners, those with disease or the faint of heart. But for individuals aspiring to reduce body fat without having to spend all day exercising, the bang for the buck is considerable. Exercise within this domain is characterized by an additional oxygen requirement (the VO2 slow component), which arises as the session proceeds. This reduced efficiency equates with an increased energy cost of work. In addition, these workloads force muscles to operate under conditions of transient ischemia (oxygen shortage), a challenge that will bring positive adaptations in cellular components that facilitate oxygen use. Cardiovascular function will be enhanced due to heavy circulatory demands and lactate threshold will be elevated.

Consequently, workloads that used to be difficult will be easy to perform. In the long run, you’ll use a lot of energy exercising between the lactate threshold and critical power, while also elevating the relatively low workload at which fat use will predominate. As a result, you can take long, relaxing walks between workouts at a faster pace with less discomfort, and burn a greater relative percentage of fat in the process.

Instead of attempting to maximize fat use during aerobic exercise, emphasize performance. If you load sufficient carbohydrates, then work above the lactate threshold for extended periods, you’ll find it easy to surpass typical fat-loss hurdles.

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: mrnatural@yahoo.com.