Which burns more calories for any set distance: Running fast or running slowly? If I run a mile fast, will I burn more calories than running a mile slowly? This question crops up sometimes. This article will answer the question, but first, why would anyone care?
Initially, this might seem like an answer that might be useful and I can see why it gets asked. If someone started running as part of a weight loss plan, they might wonder if they will burn more calories running fast for a short time, or running slower for longer. So, does running faster burn more calories?
In reality, it’s a largely conceptual question rather than one of actual use, because running progression plans should not be based around calorie burn. Instead running plans need to keep in mind that recovery is just as important as the training itself. If the answer to the question turns out to be that running faster burns more calories over any particular distance, you can’t suddenly change five runs a week to fast runs. That way would lead to injury. Most of your runs should be an easy effort and that shouldn’t change, just to eek out a few extra calories. Still want to know though?…
Which burns more calories: Running fast or running slowly?
There are a few aspects to consider here: Background calories, Run-specific calories and Afterburn calories.
Background calories
The body burns calories all the time, just to stay alive – your basic metabolic rate. This background level of calorie burn exists when you go for a run too. If you run for 60 minutes, that background calorie burn will be double the background burn of a 30 minute run and a sports watch might include that value. However, that calorie burn would have happened anyway, whether you were running or lying on the sofa!
Run-specific calories
These are the extra calories that are burned specifically by increasing your effort level from “sitting on the sofa” to “going for a run”, just during the run. The problem comes with measuring calories used. Normal energy expenditure methods involve measuring gas exchange with a mask to measure the amount of oxygen / carbon dioxide going in compared to coming out, which can be used to estimate how much fuel was burned during aerobic exercise. However, this doesn’t account for the energy cost of anaerobic energy systems (Lactate). The aerobic system is very efficient, but slow to produce energy. The lactate system that ramps up during faster efforts is much faster to produce energy, but much less efficient, consuming more calories per unit of energy.
If we put that omission error aside for a while, studies show that average ability runners use the same amount of aerobic energy to cover a distance whether they run it fast or slow (linear relationship), whereas sub-elite runners have a curved relationship where there is an optimum speed for running economy.
However, when you take into account the (unmeasured) energy cost of anaerobic processes, running a mile fast will burn more calories (over and above background calories) than running it slowly.
Additionally when you run faster, you recruit more muscle fibres due to the faster movement and increased range of movement. I couldn’t find research on the impact of that area though, if any.
As an aside, we know that walking a mile uses significantly less calories that running it, because it’s a completely different, more efficient mode of movement.
In theory, running faster should have an air resistance energy cost, due to the exponential increase in difficulty of pushing through the air at higher speeds, but in reality this is negligible – the speed delta between fast and slow isn’t great enough.
Afterburn calories
When you run fast, there is an “afterburn” effect that elevates your basic metabolic rate for a few hours after the run, higher than if you’d done a slow run. This means that if you run fast for a mile, afterwards while sitting around on the sofa, you’d burn a few more calories than if you’d run a mile slowly.
Summary
Does running faster burn more calories? Yes, overall, running a mile fast will burn a few more calories than running a mile slowly.
However, it’s a fairly pointless piece of information, because you can’t use it for weight loss due to the increased injury risk of doing all your runs fast. Instead focus on gradually improving your overall resilience to running, so you can do more running each week.
