Have you ever blown up in a race and had to run the last few Kms or Miles about 1min slower than you started?
YES. Of course you have. We all have!
I will tell you why you blew up and how you can go faster next time.
You started too hard, bro!
Why does pacing matter?
As humans, we can only exercise at high workloads for short durations. The higher the workload, the shorter duration.
Typically, scientists and running coaches use our anaerobic (lactate) threshold (LTH) as the benchmark for what is sustainable for about an hour. How far and how long you can exercise above your anaerobic (lactate) threshold is referred to as your anaerobic work capacity (AWC).
Regardless of whether you’re an elite runner or a mid-pack marathoner, your anaerobic work capacity is LIMITED. I.e. you can’t sprint for 2hrs.
Fatigue is complicated, and human bodies can be forced to slow down due to factors other than our body’s available energy fuel. Neuromuscular capacity, core temperature, hydration status and the course terrain are all factors that can cause us to slow down during a race. For now, I’ll keep the scope of the chat to metabolism and fuel utilisation.
It’s all about Carbs and Lactate
Once we work above our AEROBIC threshold (not anaerobic), we begin burning carbohydrates and accumulating byproducts of carbohydrate (glycolytic) metabolism, namely, lactate and H+ ions.
OK, Dr Will, YOU LOST ME.
Exercising Metabolism 101, Recap
Lactate can only come from carbohydrates.
Carbohydrates can be burnt (oxidised) in the presence of oxygen (aerobic) AND in the absence of oxygen (anaerobic), making carbohydrates such a powerful fuel.
Fats, proteins, and ketones can only be metabolised in the presence of oxygen, which makes them slow fuels. Ok for cruising around an ultramarathon, but not so helpful when we need energy fast.
As we start to increase our exercise workload (intensity), our energy requirements speed up. To sustain the energy supply to the working muscles, we use more carbohydrates and fewer fats.
Alright, I’m still with you, just. (keep reading)
The Carbohydrate Conundrum
The problem with using more carbohydrates and fewer fats as we speed up is that we have a limited amount of carbohydrates and a near-unlimited amount of fats (relatively speaking).
Therefore, when our carbohydrates run out we’re left with our slow fats for fuel.
You’ve just hit the wall, blown up, bonked, burnt your biscuit, and ruined your race.
Our limited quantities of carbohydrates aren’t our only issue. WHAT! The byproducts of anaerobic carbohydrate metabolism, lactate and the associated hydrogen ions, are also a big problem.
It’s Not Lactates Fault
I feel bad for lactate. Lactate gets blamed for people’s sore legs and shitty races.
Lactate isn’t the cause of you ‘blowing up’ it’s more like the messenger of unsustainable work, like, “Hey, you’re going too hard, bro.”
The unfortunate situation for lactate is that it’s always there when you go above and beyond your anaerobic threshold, so it makes sense that it’s the first thing you’d blame. Kind of like that mate you have that always ‘convinces’ you to have another drink (or 10). They’re not the ones to blame for your hangover 😮.
Lactate doesn’t exist as lactic acid in the muscle. Instead, its reaction colleague hydrogen ions (H+) is the real acid, and it’s H+ that is the culprit of the ‘burning’ sensation.
Lactate can help you! Lactate can be converted into useable forms of energy (like carbohydrate) in the very muscles it’s blamed for harming. Oh, the irony 😞.
How you can go faster next time?
Recap. The faster you run, the more carbohydrates you use for fuel. Carbohydrates are limited. When we use them up, they’re gone.
We have two important thresholds; aerobic and anaerobic.
To run faster in your next race, you need to know your thresholds to use your training zones for pacing.
The easiest way to find your anaerobic threshold is to go run hard for an hour…. but no one wants to do that. So, the next easiest way is to use your past training data.
- Threshold Running Pace = Take your best average running pace for 40-60min from the last 6 months.
- Threshold Running Heart Rate = Take your average HR from the last 20min of a 10km or half marathon within the last 6 months.
- Threshold Running Power = Complete a 1km and a 5km time trial with at least 3 days in between.
Once you’ve got your training zones sorted, you can start to use your zones as intensities guides for pacing your races and training.
If you start running a marathon above Zone 3, you’ll burn too much carbohydrate and end up walking. Likewise, you can’t expect to run your best 5km by starting at 115% of your threshold.
I recommend doing some test runs of half your event distance at the bottom end of my training zone references (pictured above). If you can complete those test runs reasonably well, you can begin to test longer runs at higher intensities.
The goal is to build up, not fall down.
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