Tuesday, September 16, 2008

Lactate Thresholds

In my first blog entry I said I'd talk about training for the Leadville 100 MTB race. So far I haven't done much of that, in part because we haven't really started our focused training for the 2009 race yet.

So this is the first "real" training entry, but it won't be the last.

After our unsuccessful attempt to ride Leadville in 2004 Phil and I took a few days to lick our wounds, then we sat down and came up with a plan which we hoped would allow us to succeed in our next attempt.

The first step of that plan was to have lactate threshold testing performed at the Boulder Center for Sports Medicine. We hoped the information we learned could then be used by a coach to help develop a training plan tailored to our fitness levels.

Lactate threshold is one of the most common performance markers used by many athletes and coaches. The point is to learn the highest intensity at which you race and train before hitting the wall from high levels of lactate and metabolic waste in your bloodstream.

What is Lactate Threshold?
The energy required to move is supplied from the breakdown of adenosine triphosphate (ATP). The body can store about 85 grams of ATP and would use it up very quickly if we did not have a few ways of resynthesizing it.

There are three energy systems that produce energy: ATP-PC (short, explosive movements), glycolytic (intermittent hard intervals) and aerobic (endurance exercise).

Athletes most commonly attribute the intense burning and pain felt during exhaustive bouts of exercise to lactate, which is produced by all energy systems, but becomes an issue when it accumulates and can't be processed fast enough. When you demand energy faster than your aerobic energy system can produce it, your glycolytic energy system picks up the slack. Even though glycolytic (anaerobic) literally means without oxygen, it’s not that there’s no oxygen available, but rather that your aerobic system is going as fast as it can and you still need more energy. The glycolytic system is fast because it doesn’t use oxygen to burn carbohydrate, but it’s less efficient and produces less energy, per unit of fuel burned, than the aerobic system. Your body has to clear lactate from working muscles and process it back to useable fuels, and lactate threshold is the point at which production outstrips the clearing process and lactate starts to accumulate in the muscles.

Why Lactate Threshold Matters
Your lactate threshold essentially defines the upper limit of your sustainable efforts in training and competition. Once you cross over and rely more heavily on your glycolytic system for energy, you’re exercising on borrowed time. The accumulation of lactate will hinder your muscles’ ability to contract, and you will be forced to slow down or stop.

The more work you can do before reaching lactate threshold, the better. If the pace you can hold at your lactate threshold is higher than the pace your competitor can hold at his or her lactate threshold, you go faster, reach the finish first, and win. Being able to do more work at lactate threshold also means maintaining a lighter pace is even easier. While your main rivals are burning energy fast, riding at their limits, you can stay right with them and rely primarily on your aerobic system. This saves valuable energy for hard efforts later.

An athlete’s initial lactate test provides an indicator of fitness level and a starting point for training. Depending on the protocol used, the following data can be acquired through a lactate test: maximum sustainable power (cycling), recovery heart rate (how quickly the athlete’s heart is able to return to recovered levels), speed and power at lactate threshold, and a relative index of fitness (i.e., speed or power divided by the athlete’s body weight).

The real power of lactate threshold testing comes from comparing test results over time. Provided you’re training and striving to improve, regular lactate testing provides you with concrete evidence of improvement, or lack thereof, throughout the season. A history of lactate tests should show changes in fitness, characterized by: increased power and/or speed at threshold, improved recovery heart rate, a higher lactate threshold heart rate, and a higher speed- or power-to-weight ratio.

Consistency is the key to improving performance at lactate threshold. You have to accumulate a lot of work at a steady workload to place the appropriate amount of stress or load on the system. Since you can’t spend a lot of time working above threshold, these training intervals have to be at an intensity just below your threshold.

In subsequent posts I'll talk more about how to use your lactate threshold (LT) when developing your training plan.

I am being re-tested at the Boulder Center for Sports Medicine on October 2, so I'll also provide details of my test and how I will use that information to structure my training plan for the 2009 season.

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