Most people have probably heard about lactate or lactic acid before in passing, though possibly incorrectly. I know growing up I was always told to move around the day after a tough soccer game, because of the “lactic acid buildup” causing soreness. Well, sorry coach (aka dad) – lactic acid doesn’t cause muscle soreness in the days after workouts.
However, lactate does provide some key insights into energy metabolism during training, and that has implications on structuring your training routine. This is where you may have heard the term “lactate threshold.” That’s what I’m hoping to break down for you today.
Why even think about this? Many training plans now will use zones based on heart rates that are a certain percent of this thing called lactate threshold (more on that below). Years ago, you probably frequently saw training based on max heart rate percentages. However, the common formula for max heart rate (220-age) is super inaccurate.
For example, if you did this formula on me, you’d come up with a max heart rate of 189 (220-31). Yet if I look at my heart rate data from training and races, you’ll see heart rate points above this so-called “max.” Doing a lactate threshold field test to find your threshold heart rate, and basing training off that rather than max heart rate, is far more accurate.
To understand lactate threshold, we’re going to get a little sciencey here for a minute….
What is lactic acid and lactate?
The body produces lactic acid when it creates energy using carbohydrate. Lactic acid = hydrogen + lactate. These two components break apart when they are transferred to the blood stream.
What is lactate threshold?
Though there are varying definitions of lactate threshold, the one that makes the most sense to me is this: the time during exercise when you start to see blood lactate rise at an increasing rate. In other words, it’s not when your body *starts* to produce lactate, as this can happen early in aerobic energy production too. At that point, the body can clear it properly. Instead it’s when there’s a sharp trending upward rate of lactate accumulation in the blood.
Is lactate threshold the same as anaerobic threshold?
For the purposes of what most of us use it for, we can probably just pretend they are the same. In reality, they are slightly different. While lactate threshold refers to that increasing rate of blood lactate, anaerobic threshold usually refers to the point where the body shifts to using predominately carbohydrate for energy.
I’ll back up for a second here to hopefully simplify this. When you’re exercising for more than a few seconds, your body is always using a mixture of carbohydrate and fat. Ideally, it’d be great if we could just tell our body to only use fat since we have way more of that stored compared to carbohydrate. Unfortunately, there’s no way to do that.
Each person will be slightly different in terms of the precise percentage of fat versus carbs used, with mostly fat being used in lower intensity exercise. At some point of higher intensity, the body needs help keeping up with the energy needs of the muscles. In order to keep up with the demands, the body must augment the aerobic production (fat) with that anaerobic production (carbs).
So you can see that there are connections here with lactate threshold, since the rise in lactate itself is a byproduct of carbohydrate metabolism. That said, there are complexities that do not make these the exact same thing in exercise science. But for probably 95% of us, don’t worry about the difference between the two!
How do I do a lactate threshold test?
You can get this done at an exercise lab where they take blood from you and measure your lactate levels during exercise. But for most of us, that’s expensive and unnecessary. Instead, try a lactate threshold field test.
Here are two options for a lactate threshold field test:
1) 30 minute field test
A 2005 study suggests this is a fairly accurate method that can be done on your own. Warm up at a comfortable pace for 10-20 minutes. After you warm up, complete a 30 minute run at the best speed you know you can maintain for all 30 minutes. Many times, people will go out too fast and have to pull back at the end which makes for inaccurate results. Instead try to pace yourself at a rate that you can maintain all 30 minutes.
If you have a heart rate monitor, you’ll want to take the average heart rate from minute 10 to minute 30 of this run. (Yes, this means you ignore the first 10 minutes of data). If you don’t have a heart rate monitor, you can take your heart rate manually at 10 minutes and again at 30 minutes, then take the average. The obvious benefit to the monitor is you have more data points across the 20 minute time span.
As an example, here’s the heart rate data from the lactate threshold field test I did several months ago, when I was starting to train again after a little time off. This was done just looping around my apartment complex – an easy, flat surface. You can see the first 10 minutes were just a light warm up (lower pace/HR), then I went into the 30 minute field test (minutes 10-40) followed by a cool down (minutes 40-45). I was able to maintain a fairly consistent pace throughout (probably one of my better attempts, haha). If I select only the last 20 minutes of the field test, I end up with a TH HR (threshold heart rate) of around 178.
2) 5K test
Go out to a race and run the best 5K you can. Take your average heart rate from the race and subtract 10-15 bpm to get your lactate threshold heart rate.
What do you do with the data from your lactate threshold field test?
Once you have this data, you can use zone-based training plans (either that a coach develops for you or that you find online) to structure your training. Zone based plans assign workouts based on a percentage of your lactate threshold heart rate which you found in your field test.
Why train this way? The biggest benefits from endurance training come from doing the majority of your training in the easier, aerobic zones – and then building in small but specific amounts of structured anaerobic training. You don’t want to do excessive amounts of tough training because a) the benefits don’t increase in the same pattern, b) you increase your risk of injury, and c) it’s freaking hard! 😉
Different coaches will use slightly different zones, but the science behind them is all similar. The most popular set is probably this one developed by Joe Friel. If you find any free online plans, this is most likely what they are based on.
At USAT coach training, the head coach of QT2 (one of the major triathlon coaching companies) showcased their zone system, which I personally like better for simplicity:
- ZR (recovery) – 67-76% of threshold heart rate
- Z1 (aerobic development) – 80-86% of threshold heart rate
- Z2 (aerobic development and muscular endurance) – 86-93% of threshold heart rate
- Z3 (threshold endurance) – 93-100% of threshold heart rate
- BSE (anaerobic development; VO2max training) – best sustainable effort
Of course, you’ll need a plan or a coach to assign you the correct progression and number of workouts in each of these zones.
I hope this was a helpful overview of lactate threshold field tests and zone-based training!