Now you have a clearer idea of what running economy (RE) actually refers to, here are some of the factors that are thought to affect it:

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.

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).

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.

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 feel easier, especially at faster paces. 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 fibers), there are ways you can improve your running economy.

Three Ways to Boost RE:

• Increase your cadence -- Your cadence 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 around 180 or even as high as 190. Increasing your cadence 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 and deadlifts.

• 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 starting a new workout plan.