As scientific expressions go, ‘running economy’ (RE) has never been as familiar to runners as 'VO2 max' and 'lactate threshold'. But now, many exercise scientists consider RE to be the third critical determinant of distance running performance. To understand what it is, it's important to first do a quick recap of what the terms 'VO2 max' and 'lactate threshold' actually mean.
What is VO2 max?
VO2 max refers to the maximal volume of oxygen that the body can deliver to the muscles per minute.
In running, carbohydrates and fat are the primary fuels, and the breakdown of each requires oxygen (O2).
The energy needed to run at a given pace corresponds to the volume (V) of O2 consumed per unit of time (or VO2). It’s measured by comparing the oxygen levels of inhaled and exhaled air, usually during a treadmill test. Because VO2 depends on body size (larger runners need more oxygen), it’s generally normalised to body mass in kilograms and so is reported as millilitres of O2 per kilogram of body mass per minute: ml/kg/min.
What is lactate threshold?
Lactate threshold (which you've probably reached during high-intensity workouts such as hill training) refers to the point at which lactate is produced by your muscles and begins to accumulate in the bloodstream at a quicker rate than it can be removed (that lovely point in a session where your muscles are burning and you feel like you might throw up at any moment).
How do you calculate running economy?
Simply put, running economy is the relationship between oxygen consumption and running speed. If VO2 max is your upper limit of oxygen consumption (your aerobic capacity) and lactate threshold is the level of your aerobic capacity that you can sustain for a long time, then running economy (RE) is your efficiency at converting that oxygen consumption into forward motion. For any given pace, the less energy and oxygen you use, the better.
What factors influence running economy?
Now you have a clearer idea of what RE actually refers to, here are some of the factors that are thought to affect it…
1. Muscle fibre composition
Your composition of ‘slow-twitch’ (type I) and ‘fast-twitch’ (type II) muscle fibres is believed to be genetically determined because they change little over time, even when training is drastically altered. But researchers at the University of Texas have shown that cyclists with more slow-twitch fibres tend to use less oxygen to maintain a given power output. While the data for running is less clear-cut, because of the more complex biomechanics, it’s reasonable to speculate that RE also reflects one’s muscle-fibre makeup.
2. Joint flexibility
Among reasonably fit runners and walkers showing typical variations in flexibility, it appears that the less flexible are more economical on average. This somewhat surprising trend has been explained as a possible consequence of two factors: stiff joints need less muscle force (and thus less energy) to stabilise them; and stiff muscle-tendon units provide superior elastic storage and energy return from footstrike to push-off. It’s possible that, for distance runners, medium flexibility is preferable to very low flexibility (which increases the incidence of injury due to limited range of motion) or very high flexibility (which seems to worsen RE).
3. Body shape
Even though your VO2 measurement is related to body mass, smaller runners tend to use proportionally less oxygen. Also, according to the physics of rotating limbs, mass towards the bottom of the leg requires more energy to move than mass close to the trunk.
Elite East African runners tend to be unusually economical, and it’s been suggested that their small overall size and slender lower legs are partly responsible for this. A 2006 report by Spanish researchers at the University of Madrid indicated that elite runners from Eritrea had REs about 12 per cent better than a comparable group of Spanish runners.
4. Resistance on the run
Just as your car’s fuel economy depends on the driving conditions, your RE is variable according to running conditions. An uphill slope or difficult footing (such as sand, mud or long grass) raises the energy demands of maintaining a given pace. The same is also true of fighting air resistance (for example, running into a stiff headwind requires more energy). In calm air, British studies from the early 1970s show that air resistance has a negligible effect on RE at slow paces. However, a runner churning out 5:20 miles will expend about two per cent of their energy countering air resistance.
Can you improve your running economy?
One of the biggest benefits of boosting your running economy is the fact that it will make running (especially at faster paces) feel easier. And who doesn't want that?
While you might feel like your running economy is pretty much set in stone (after all, there's not much you can do about the genetic make-up of your muscle fibres), there are ways you can improve your running economy. Here are three of them:
- Increase your stride rate
Your stride rate refers to the number of times your feet hit the ground in one minute. While most beginner runners have a stride rate that falls somewhere around the 160 mark, competitive athletes tend to have a stride rate of around 180 (or even as high as 190). Increasing your stride rate while keeping your pace roughly the same means your feet aren't in contact with the ground for as long, which results in less friction, which equals better RE.
- Improve your balance
Because running is effectively just jumping from one leg to the other, over and over again, it makes sense that working on your balance and stability in a single-leg stance is going to help improve your efficiency as a runner, and therefore your RE. Try to incorporate more single-leg work into your strength training, such as single-leg squats.
- Include plyometrics
Plyometric work (explosive movements) helps to boost muscle power, which will do wonders for your RE. Plyometrics include moves such as tuck jumps, burpees and jumping split lunges. Before doing any plyometric work, make sure you're properly warmed up, and if you're prone to injury seek advice from a coach or PT before commencing, as it can be tough on your joints.