Running economy is one of the three key performance factors in running an ultra-distance, along with endurance and stamina. It is the physiological measure of the amount of oxygen required to run at a specific pace. To simplify the notion of oxygen consumption at running velocity, we can basically consider running economy as the energy required to run at a given pace .
Generally, if you have good running economy, you will feel more comfortable at faster speed than those with lower running economy. Your running is more efficient and you will be able to run faster. Since the energy requirement is not reduced at the given pace, technically you will then be able to run faster with the same energy expenditure.
In racing an ultra, the most important benefit of running economy is the lowered effort required at a set pace. This in return will lead to the increase of endurance at the set pace, which then translates to an increase of your stamina. Therefore you can cover LONGER distance with the same amount of energy spent.
If you recall, stamina is the ability to maintain a pace for a set period of time. It is your ability not only to cover a distance but to maintain a desired pace on average throughout that distance.
That means a higher running economy would enable you to run faster than the set pace, using the same amount of energy. That will translate to you covering the same distance FASTER with the same amount of energy spent.
Either way, an improvement in running economy augurs well for the pursuit of ultra-distance runs.
And it turns out that running economy plays a more crucial role than VO2 max for longer distance running such as marathons and ultras. (I will look into understanding and explaining the concept of VO2 max in future writing.)
The good news is running economy is one physiological factor that can be easily enhanced and trained with the correct techniques. You can develop your running economy by strength training, performing plyometric and increasing mileage.
Strength training has the potential to improve running economy and prevent injuries from overtraining. Many studies have also repeatedly reported the positive effects of strength and resistance training on endurance capacity and economy.
Although running does not require an extremely high level of core strength, it certainly can benefit the lumbosacral-pelvic-hip stability. With running, you are either in the air or in a single leg stance. The single leg stance requires proper timing and recruitment of core strength to prevent too much wasted energy. About 20% of expended energy while running is spent stabilizing the body side to side.
Strength training can also improve muscular-tendon stiffness and neuromuscular efficiency. The result is an increase in muscle strength and a decrease in tendon stiffness. This decreases muscle injury while maintaining very good energy return.
The recommended basic strength exercises for runners are squat, deadlift, lunge, push-up and plank. For squats, deadlifts and lunges, you can start with body weight and then progress with loads by using dumbbells, kettlebells or barbell with weights.
They key here is to make sure that strength training is only supplementary, in that it replaces some of your total running sessions so you aren’t just increasing fatigue.
Plyometric training is another good option you can work with to improve running economy. It is generally considered high intensity activity and can be a good addition to your running programme.
Basic plyometric exercises include skipping, jumping jacks, rope jumping and box jumps. Additionally you can also work with short segments of light bounding where you run and bounce to increase flight time just a little for 5-10 strides during your run workouts. Once you are ready, you can then progress to running-specific plyometric such as sprinting and uphill running.
Explosive running is seen to be the most running-specific form of plyometric training. Sprints and uphill running bouts of up to 30 seconds have been shown by research to significantly improve running economy.
My approach to explosive running is run 5 to 10 sprints on flats or small inclines for 20 to 30 seconds with recovery in between. Recovery can be walking or easy jog of up to 5 times the sprint duration. I do this once a week, or maximum twice (but never consecutive days) if I feel stronger in general.
There is a somewhat linear correlation between running volume with running economy. Aerobic state running (easy runs) improves running economy. The more you run, the more efficient your cardiovascular becomes, provided you stay free of injury.
Therefore there is a limit of how much you can improve running economy by increasing volume. You want to avoid the slippery slope of injury, burnout and overtraining resulting from unsustainable high running volume.
When increasing mileage, a conservative approach to avoid injury is to increase the total distance by not more than ten percent per week.
Finally I just have to add that another logical way to improve running economy is by losing some weight! This may not apply to everyone especially if you are not overweight to begin with. To a certain degree, running economy is dependent on your total body weight. Carrying more mass means using more energy. So if you ever want to squeeze out extra running economy, maybe look at the extra mass that is not functional such as, some body fat. Oops.
For more on how to improve running economy, I find this article in Team Norris Running insightful
 In the field of exercise physiology, oxygen consumption (VO2) is the golden standard for measuring exercise intensity. Both oxygen consumption and energy expenditure (EE) of working muscles increase during exercise. Oxygen consumption is thus intimately linked energy expenditure.