Speed work for ultrarunners - why it matters and how to do it
You’re probably thinking: “my pace on trails is slow - why do I need to do speed work at all?”. This is a great question! To understand the importance of speed work for ultrarunners we turn to the theory of our energy systems (how our body does work) and how their efficiency (or lack thereof) impacts our ability to perform at longer distances when the body is stretched beyond its limits.
Energy systems
Our body has three energy systems:
Immediate, short-term use: ATP-CP (think the first 10 seconds of a sprint)
Short term use: Glycolytic (sprint-tempo)
Long-term: Oxidative (your long runs)
It’s important to note that all three energy systems are “on” at all times - the percentage each is used just changes based on how hard we’re working. Most people speak about these systems as being either “aerobic” or “anaerobic”, but this is actually a misnomer! Producing energy always requires oxygen (otherwise you wouldn’t be alive!) the method by which energy is produced just changes between the three systems. We won’t dig into the theory beyond this, just knowing that you body produces energy differently depending how hard you’re working is the key-takeaway, as the type of speed workout you do corresponds to training a particular energy system.
Definitions
Before we start talking about VO2 max and Lactate Threshold (LT) we should probably define what these mean:
“The term maximum effort heart rate or VO2 max is often used among endurance athletes. It relates to maximal oxygen consumption or, more specifically, an individual’s maximal capacity to transport and use oxygen during exercise. The V stands for volume, O2 stands for oxygen, and max refers to maximum.” (Koop)
Practically speaking, this is your absolute maximum upper limit of work. When we do intervals (short sprints 60 seconds-three minutes in duration) we are encouraging improvements in our VO2 max. While running intervals, we want to be operating at 90-95% of our maximum heart rate.
Lactate Threshold: LT is most commonly used to describe the working upper limit of one’s aerobic capacity. LT represents the level at which blood lactate accumulates in the bloodstream (it is not “cleared” in the muscle and used for energy). This occurs when lactate production exceeds lactate clearing. In practice this means you cannot maintain an effort that is over your LT for long.
A Tempo Run is designed to keep you operating just below your LT and improve this system. You LT is typically between 80-90% of your maximum heart rate and may correspond to your 10k race pace.
**Note: you may have heard the term “lactic acid buildup” before as described as the culprit for that burning, heavy feeling in your legs when you’re pushing hard. This is another misnomer! Lactic acid does not exist in the human body, and lactate is a good thing (energy source); it is not responsible for the burning you feel in your legs.
—> Practically speaking, you can associate your LT to a specific heart rate by doing a Talk Test. If you’re interested in determining your LT, let’s talk! Watches like Garmin and Coros also do their best to estimate LT and VO2 max, but please be warned that these are a best guess based on your previous performance history. Many watches allow you to do a test workout to more accurately measure.
Ok, I get it…but why do ultra runners need to do speed work again?
Multiple studies have shown that integrating speed work into your training improves your ultra performance. But why is this? Think of those three energy systems we mentioned above making up the support system of a suspension bridge (the bridge is your overall fitness level). If you raise one supporting system, the whole bridge will rise! So, if you want to improve your 5k time: do speed work. If you also want to improve your 50M time, DO SPEED WORK!
As you get into the later stages of an ultra, your slow-twitch muscles fibers will be tired, which means your fast-twitch fibers will be recruited to help handle the load. If you haven’t trained your fast-twitch fibers, they won’t do a very good job at supporting you later in the race!
A common trend seen in endurance athletes is their Lactate Threshold (LT) is strong, but also very close to their VO2 max. This means their overall potential as runner is limited by their poor VO2 max. As in our bridge analogy, if they want to get faster overall and perform stronger in their races, they should focus on integrating VO2 max workouts.
The workouts
Now that you understand the energy systems and some basic terminology, let’s talk about the workouts!
VO2 Max: Running Intervals
Running intervals ultimately help to improve your heart’s stroke volume (how much blood your heart can pump in a given beat) and maximum cardiac output. Interval also improve muscle capilarization (blood and oxygen delivery to your muscles) and blood plasma volume, helping you tolerate heat more effectively. The benefits are endless!
Example: 6x2 minutes - this equates to 12 minutes total time at intensity
Work/rest ratio: 1:1 (if you’re doing 2 minute intervals, you rest for 2 minutes in between)
How to do it: intervals are close to an all-out sprint and your effort level should be a 9/10. Note that when we say 9/10 effort, that means a level 9 that you can sustain for the duration of the interval. While you may slow down a tiny bit for the last 15-30 seconds of your interval, you want to be able to finish. Intervals take trial-and-error to find your sweet spot. Once you do these for awhile you’ll have an idea of what your heart rate should be as well (generally 90-95% of max heart rate). For me, I try to hit 174-176 bpm during my intervals. You can perform intervals on hills, which actually considered a safer approach as it puts less stress on your body. You can also perform intervals on an elliptical! This is one of my personal favorites as I feel I can ramp and control my heart rate more effectively.
Example interval workout - 6x2min + 4x1 min
Notice the slight increase in heart rate interval-to-interval - this is what we’re shooting for!
Tempo/Threshold Runs (LT benefit)
In Tempo Runs (also referred to as threshold runs) we’re working our LT system by operating just under our LT. Much like Running Intervals, Tempo Runs also offer great benefits, such as increasing the size and density of mitochondria in your muscles. This improves your ability to use fat and carbohydrates as fuel, as well as lactate (as mentioned above).
Example: 3x12 minutes - this equates to 36 minutes total time at intensity
Work/rest ratio: 2:1
How to do it: Tempo Runs are done at a 7-8/10 effort level, or 80-90% of your maximum heart rate. Tempo Runs also consist of intervals, but the intervals are longer: your ideal time at intensity increase from 12 minutes with Running Intervals to 35-40+ minutes - yeah, that’s a long time!
Example Tempo Workout: 3x12 minutes
You can see from this graph that you want to get to your tempo heart rate quickly and hold it steady during the intervals.
Putting it all together
Speed work is an essential part of any ultrarunning training plan and will help you perform later into your race. The benefits from Running Intervals and Tempo Runs are endless. If you’re new to speed work, we’ll make sure to ease you into this and keep you doing speed work safely. There are options like hill repeats and elliptical workouts that offer the same cardiovascular benefits but keep your frame in tip-top shape! If you’re interested in learning how these workouts fit into your training plan, see my blog on Periodization.
Running workouts for ultramarathon success
The exciting and rapid adaptations from speed work