It’s spring, which means that it’s time for tempo work out on the trails. When I work with athletes that have big summer or fall race objectives, I often consider their middle Threshold block to be the real substance of their training. For many runners it can also be the hardest; unlike the first VO2 Max block, where runners are doing lower volume at higher intensity, or the final Endurance block, where they do higher volume at a lower intensity, the Threshold block is right in the middle. It’s medium volume at medium intensity, which often means the training stimuli stack up in a way that feels different (read: harder) from the other points of the season.

The Threshold block usually involves workouts that are done at our near your lactate threshold, which to many runners can be an abstract, moving target, hard to find and even harder to run at. Yes, you can get a lab test done and get quantitative numbers for your lactate threshold, but even this is not definitive – a runner’s threshold can change throughout the season and definitely season to season, and while the results from a lab test are very useful, if you want to run at your lab-determined threshold then you become a slave to heart rate numbers on your watch. I prefer that my athletes learn how to intuitively judge their effort and exertion because it develops a mindfulness in their running that helps in training, racing, and general life.

Your Lactate Threshold

We should pause for a moment to clarify what it is exactly we’re talking about. I’m going to provide a Cliff’s Notes version of a lactate threshold definition here, as there are many better places to get into the nitty-gritty science of this controversial topic. In fact, as that article by Iñigo San Millán points out, it’s probably time for new terminology around what the lactate threshold is; but until we develop that I’m sticking with the old.

Lactate is a byproduct of the use of glucose by muscle cells, and it’s even formed while running at easy paces. When you’re just cruising along in Zone 2, your body has no problem recycling this lactate into energy and carrying away H+ ions with it. However the more glucose a cell uses, the more lactate is produced. And when you’re really pushing, your fast twitch (Type II) muscle fibers use a lot of glucose and produce a lot of lactate. As ATP is turned over for energy, more and more protons get produced and the cellular environment gets more and more acidic. This lowers the pH of the muscle environment, which makes it harder for the muscle to work as strongly and efficiently as it can. This makes it hard and uncomfortable to run.

Luckily our body can clear lactate out of our muscle cells by exporting it into our blood, carrying away some protons with it. This process doesn’t happen instantly – in fact for most amateur athletes it can take a number of minutes, while the lactate is being produced in the muscles in a number of seconds. As athletes train and get more fit, their ability to quickly and efficiently clear lactate from their muscles increases. Running hard is not the only way to train this ability in our bodies – in fact, running at easy Zone 2 low RPE efforts is just as important. We obviously can’t do threshold intervals all of the time, so when we do it’s important to do them correctly.

Don’t let your cup overflow

The “cup of water” analogy is often used to describe the lactate threshold in non-scientific terms. Imagine there’s a cup of water on the table with a very small hole toward the bottom of it. If you pour water into this cup, it’s going to drain out of the hole at a rate determined by the size of the hole. Pouring water into the cup is the equivalent of your muscles producing lactate after using glucose, and the water coming out the hole is the equivalent of your body clearing out lactate into the blood. If you pour water into the cup at the same rate that the water is draining out the hole, you are effectively at your lactate threshold. You can run at this rate for a decent amount of time, around 20-30 minutes for most athletes, and up to an hour for those with lots of experience. If you increase the rate of pouring water into the cup, eventually the hole will not drain fast enough and the cup will overflow. You have just gone over your lactate threshold – here, you can only run for a handful of minutes before needing to slow down and recover.

So how do you find your lactate threshold without using your heart rate and a heart rate monitor? I find three methods useful when you’re out there on the trail.

The Talk Test

One of the easiest and most intuitive methods to determine when you are approaching your lactate threshold is often called the “talk test”. When you are running easy, well under your lactate threshold, you should be able to breathe regularly and even hold a conversation with a running partner. We often call this “conversation pace”, and it’s a great mark of low RPE and low heart rate zone running.

As your effort and intensity increase, the rate of your breathing does too. For me, this is the first and most apparent change that I notice. As I approach my lactate threshold, my breathing becomes noticeably more rapid as my heart rate and effort increase. At some point it becomes very difficult for me to speak in full, complete sentences. The easiest way to test this is to actually try it – I like to say “I can still speak in complete sentences” when I’m out there running on the trail. Yes, I look like a bit of a fool talking to myself in the middle of the mountains, but I already look like a bit of a fool running repeats up a hill by myself.

When I’m approaching my lactate threshold I can barely get a full sentence out before gasping for air. What this sounds like in practice is something like “I can still speak in complete sentences… gasp…. gasp….deep breath”. Sometimes I do think runners don’t go hard enough here, and assume that if they can still get a full sentence out they are at the right level of effort. However it’s important to note that you should barely be able to get a full sentence out – if you can easily complete your sentence and start another one than you are actually still at conversation pace.

For some runners that are having difficulty with the talk test or with finding their threshold I ask them to do the talk test while doing some VO2 Max sprints, just to know what failure in the talk test feels like. Next time you’re out there doing a 3 minute full out effort, try to start talking in the middle of it – you shouldn’t be able to get through your sentence. Often times it’s helpful to know what the failure case feels like to know when you are succeeding at your threshold run.

Hitting that threshold in Circus Maximus

Increased Mental Focus

The second method that I think is useful to determine when you’re running at your threshold is when you noticeably need an increased level of mental focus to continue running at the same effort. For me, this method can be just as useful as the talk test, but it is admittedly a bit more abstract and hard to perceive at first.

When I’m parked at my lactate threshold during an interval it’s hard, it’s uncomfortable, and it requires complete mental focus to stay running at that pace. I often focus on just the immediate task at hand – my breath, my footsteps, and moving smoothly while maintaining that level of intensity. If my mind begins to wander, my effort and heart rate immediately decrease – if I start thinking about the grocery list, or how I’m going to pick up the kids later, or when will this interval ever end, I instantly lose authenticity in the workout and I am not at my threshold anymore.

This is one reason these intervals can be so effective at preparing runners for long races and objectives – they are just as much of a mental workout as they are a physical one. For many of my athletes the execution of threshold workouts becomes easier once they realize this key concept. It’s not only physically uncomfortable, but it can be mentally uncomfortable too, as you have to allow your mind to fall into a complete present and meditative state. It’s the exact same skill that you use when you’re in the pain cave in the middle of a long outing in the mountains – the only way I survived the tough parts of my 2021 UTMB lap was to stay completely present and literally tell myself “Be right here”.

It can feel intimidating to maintain mental focus for some longer threshold workouts, and so I often recommend using the timer on your watch to your advantage. If you’re doing a 20 minute effort, set your repeating alarm for 5 minutes and know that you’ll need to be pushing it at your threshold for 4 of those timing cycles. This allows you to get brief check-ins along the way that will subdivide the longer period of time and make it feel more manageable. Just like running from aid station to aid station in a long ultra, running from short time period to short time period will eventually get you to the end of the longer distance.

Body Tightness and Restriction

A third way to know when you are at your lactate threshold is to monitor and scan your body for tightness and restriction. For me, this is usually a sign that I’ve gone too far and possibly surpassed my threshold, but this is still an important thing to know when you’re in the middle of a workout. If you start sensing body tightness in your chest, back, arms, or shoulders it’s a sign that you’re pushing too hard and that effort is likely unsustainable for the duration of the interval. The first step is of course to try to consciously relax – this is always a good idea while running, and especially while running hard. If this doesn’t work then it’s time to back down your effort again, reign in your mental focus, try to get out a full sentence, and recalibrate.

All you need for an LTHRT is a never-ending hill, a heart rate monitor, and some mental fortitude

The Lactate Threshold Heart Rate Test

Once you’ve practiced the above three methods for determining when you’re running at or near your lactate threshold, it might be time to try a lactate threshold heart rate test (LTHRT) on your own. This is essentially the DIY method of calculating your heart rate at your lactate threshold, and can be surprisingly accurate when compared to actually going into a lab and getting hooked up to a bunch of machines on a treadmill. It requires nothing more than an accurate heart rate monitor (the optical wrist monitor on your watch probably isn’t enough – try to use a chest strap or arm band if you can), a long runnable hill gradient, 30 minutes of your time, and a heaping serving of that mental focus we talked about above.

David Roche goes into great detail about this procedure, and how to extrapolate your HR training zones once you have your threshold, in his article here. The tl;dr of it is that you do a 30 minute time trial where you try to go as hard as you can without degrading the pace or effort, and then take your average heart rate for the final 20 minutes of the effort. I like the free Strava Sauce plugin for analyzing basic data like average heart rate on your activities. Keep in mind that your threshold HR will likely change throughout a season and definitely across the years, so it can sometimes be useful to perform a LTHRT multiple times throughout a training block (and it’s a pretty good workout too).

A well executed LTHRT graph

Thanks for reading and I hope the above methods and explanation are useful to your training. The more perceptive and intuitive you can be with your own body and mind while running, the smoother and more efficient you will be both on the trail and off the trail in your daily life. Now go forth and run at your threshold!!!

Mat is currently living in the French Alps, where he’s surrounded by steep trails just begging you to go out and do an LTHRT on them. Head on over to flowstaterunning.com to learn more about his coaching offerings and philosophy.

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