An In-Depth Look at Running Economy
Different Types of Efficiency
Running economy is often presented, along with VO2 Max and lactate threshold, as a good predictor of running performance. While VO2 max is a good indicator of your running potential it is not the best indicator of running performance for runners of similar classification. Leaving aside issues with VO2 Max and lactate threshold, in this article I want to explore the role of running economy to performance and its value to the average recreational runner.
In simple terms, running economy (RE) tells you how efficient you are at using energy while running. It's analogous to a car's fuel efficiency. The more efficient you are the less energy you're using to run at a particular speed. (Exercise physiology sticklers may take issue with using the terms economy and efficiency interchangeably but this isn't an academic paper and for my purposes it works.)
By being more economical a runner with a lower VO2 max can run faster than another runner with slightly higher VO2 max.
Traditionally RE was expressed as a percentage of VO2 Max so it told you how much oxygen you were consuming at a particular speed. But a method developed in 2009 expressed RE in terms of calories used and claims to be more sensitive to changes in speed compared to expressing RE in terms of oxygen cost.
Factors Making Up Running Economy
Even though it's a very useful metric, there's still debate about what's exactly involved in determing RE and how much each factor contributes to it. I'll outline below what I think the major factors are that make up RE and how to train to improve each factor thereby developing better RE.
I have to give credit to Steve Magness, a Nike coach, and two older studies on RE, one by Williams and Cavanagh and the other by Saunders et al. for helping progress my thoughts about RE from the traditional point of view.
RE is the sum of different types of efficiency. Breaking down RE into sub-categories makes it easier to understand why a runner may have good RE and how different training methods can help you develop better RE.
I've chosen four types of efficiency that combine to determine your RE; biomechanical efficiency, neuromuscular efficiency, physiological efficiency and metabolic efficiency.
Biomechanical Efficiency (BmE)
Basically this is the position of your body and various limbs during various stages of the running gait. How much do your hips, knees and ankles flex and extend? How is the position and motion of your shoulders and torso? Where does your foot strike in relation to your center of mass? How much Ground Reaction Forces do you create with each footstrike?
The stiffness of your muscles and how well the elastic recoil mechanism in the muscles, tendons and fascia works along with other attributes combine with body position to determine your individual running gait. Joint angles, body and limb position, force plate readings and similar measurements can be used to quantify running biomechanics.
Neuromuscular Efficiency (NmE)
Neuromuscular efficiency also refers to gait, though the focus here is on the nervous system and how good it is at firing specific muscles at the right times to create efficient running.
How strong a muscle contracts could also be included in this category. The ability for your nervous system to cycle through the muscle fibers of different muscles is another possible sub-factor. Being able to cycle through more muscle fibers means the muscles could work for longer before fatiguing. The actual ability of your muscles to work for long periods would also affect neuromuscular efficiency.
This would be measured by things like EMG of muscles, force plate readings, etc.
Physiological Efficiency (PhE)
Physiological efficiency refers to how well the circulatory system is able to deliver oxygen and nutrients to your muscles and how well your muscles can uptake O2 and nutrients. It could also include the denisty of mitrochondria (the powerhouses in your cells) in your muscles and how well your system can clear waste byproducts out of your muscles and other tissues.
Your breathing and your pulmonary system's ability to draw oxygen out of the air into your blood and likewise clear carbon dioxide would be other attributes in this category.
Lactate threshold and aerobic threshold would be two traditional measurements you could use. Measuring mitrochondrial density could be another thought this usually isn't done outside of research studies. Breathing rate may be another measurement to use though I haven't seen this used so I'm only speculating here.
Metabolic Efficiency (MeE)
Metabolic efficiency refers to how well your body breaks down energy sources such as fat and glycogen to provide fuel for the working muscles. This is measured by the respiratory exchange ratio from which it can be deteremined the ratio of fat and carbs you're using as energy.
Bob Seehobar, endurance coach, athlete and nutritionist, uses the term Metabolic Efficiency as the name for his approach to training endurance athletes.
My friend, Mike T. Nelson, has coined the term Metabolic Flexibility to describe the optimal condition where your body can use carbs or fats for fuel efficiently at the appropriate times.
Both are saying almost the same thing; as a runner you want your body to spare glycogen as much as possible and enhance fat use to improve your performance. The better you are at using fatty acids for energy the more metabolically efficient you are.
Training to Improve Running Economy
In short the formula for RE is:
RE = BmE + NmE + PhE + MeE
Keep in mind this is a theoretical construct as opposed to a strict mathematical formula. I couldn't begin to tell you what proportion each factor contributes to overall RE. The various papers I've read on RE have provided estimates for some of the factors, biomechanical being the one most often cited, but I think the researchers were making educated guesses at best.
To really develop your RE you should use a training program that causes adaptations in each of the factors affecting it. A variety of methods should be used to improve each different efficiency.
Improving Biomechanical and Neuromuscular Efficiency
Mobility or flexibilty deficits could definitely affect biomechanical efficiancy so doing some mobility and flexibility work may benefit certain runners. Strength training using exercises that go through a full range of motion is another way to develop mobility while improving strength as well.
Strength training has also been shown to improve RE. Heavy weights with low repetitions and adequate recovery between sets is the deal here. Greater strength will build a bigger pool of muscles fibers you can access.
Plyometric and ballistic exercises have also shown to improve RE. Being able to produce more force and improving the elastic recoil of muscles, tendons and fascia are probably the biggest benefit of doing plyos (thinking jumping type exercises) and ballistic (fast, explosive) exercises.
Range of motion and skill drills like A's, B's and C's along with many other running drills could be of benefit here.
Practicing running with "good" form is another way to improve biomechanical and neuromuscular efficiency. Getting some outside help could be of benefit here to determine what aspects of your running gait may need work. For example you may need to change how you swing your arms or hold your torso.
And finally training at the specific paces and on the terrain you plan on racing will help your RE at those specific speeds and surfaces. One study showed that track runners had better RE running on track while orienteers had better RE out on the trails. Each group was more economical on the terrain they ran most. (Not exactly earth-shattering news is it?)
Running more mileage may also improve RE as some studies have found. The danger here of course, is that each individual will have a different threshold on how much mileage they can run. (But that's an entirely different subject that I'll address in another article).
Improving Physiological Efficiency
Running at different paces can help develop physiological efficiency as can running more miles. Putting in longer runs at lower intensity along with shorter runs at higher intensity will impact different elements of your physiology so you need to include both ends of the spectrums in your program.
Lower intensity training will help your central physiological adaptations (think of heart and lungs) while higher intensity training (speed work and such) creates more peripheral adaptations (legs and arms).
Cross-training in other endurance sports such as cycling or cross-country skiing could also provide some benefit if you are limited in how many miles you can run each week. But keep this training at moderate or lower intensity as the cross-over benefits from higher intensity cross-training are diminished (see above, peripheral vs central adaptations).
Specific types of strength training such as strength-endurance and power-endurance training can also improve physiological efficiency primarily through peripheral adaptations.
Improving Metabolic Efficiency
Training at lower intensity as well as nutritional strategies can improve metabolic efficiency. Doing some fasted, aerobic pace training can help develop fat burning capabilities.
Limiting your intake of carbohydrates during periods of lower volume training can help develop your body's ability to burn fat. During periods of more training or higher intensity training, you would increase your intake of starchy and sugary carbohydrates (think breads, pasta, rice, sweets). This is basiscally Bob Seehobar's approach.
Intermittent fasting (IF) can also be a useful tool though individual responses to this may vary a lot. Mike T. Nelson uses IF in his approach and it's the one that I've used successfully to improve my own metabolic efficiency. I'll share my experiences in another article.
Practicing taking in fuel during long duration runs will help you determine what your body can tolerate and train it to take in outside sources of fuel during those long runs.
Other Factors Influencing RE
The surface you run on can impact RE with a relatively compliant surface being the best for RE. Think of it as the Goldilocks type surface, neither too hard or too soft. You want it hard enough to be able to provide good energy return but not too hard. Likewise, too soft a surface will rob you of the elastic recoil and decrease your RE.
Body type can also have an influence on RE. Most elite distance runners are built very similarily - not too tall, lean and have small calves. Weight can play a big role as well. So while you may not be able to do much about your height or the structure of your hips, keeping your body weight in a healthy zone and staying lean will help your RE.
Alititude training and training in the heat have also been shown to improve RE.
Footwear can help or hinder RE. Too heavy a shoe can decrease RE as you're carrying more weight at the end of your limb. Some cushioning but not excessive seems to improve RE.
Breaking down RE into categories can also help explain some apparent contradictions. Some elite runners have been criticized for having what appeared to be less than ideal running form but yet still had good RE. So while they may not have had great biomechanical efficiency, they may have had excellent neuromuscular, physiological and metabolic efficiencies that more than offset the biomechanical deficit.
You can see there's a lot of overlap in the training effect of different training methods. We like to compartmentalize subjects like RE and break them down to make them easier to understand. But in truth, biology is a messy science. So whenever you train whether it's running, weight training or cross-training it affects the whole system not only one specific sub-system. One type of training will impact more than one efficiency.
The take away for runners is to understand RE is made up of a number of components and it will pay to use a variety of training methods to develop each of these components. Where many recreational runners fail is they neglect one or more types of training thereby limiting their overall development of RE.
A few of the key methods many runners neglect to incorporate into their training are working on running technique, strength training and maximizing their metabolic efficiency.
I hope by understanding how these methods can impact RE you'll be more likely to use them.