Running Economy: The Hidden Factor Behind Endurance Performance
Understanding VO2 Max:
The Key to Endurance PerformanceVO2 max is a measure of an individual's maximal oxygen uptake, reflecting their body's ability to consume and utilize oxygen during intense exercise. It is a crucial metric in assessing aerobic fitness and endurance capacity. The higher the VO2 max value, the more oxygen a runner's body can deliver to the muscles, enabling them to sustain a high-intensity effort for longer durations. VO2 max serves as a valuable predictor of endurance performance and plays a significant role in determining an athlete's potential.
To test this, we will usually do a continual ramp test starting at walk pace (normally 4km/h) and increasing in 1km/h increments until the athlete reaches volitional fatigue (the point where they can no longer continue increasing the pace or maintain the pace they are running)
The above graph plots oxygen consumption (Green line), CO2 production (red line) and Heart rate (blue line). This test is usually to establish an athlete's aerobic capacity and also can be used to determine current Aerobic and Anaerobic Thresholds to set training zones and measure changes in fitness. However, for endurance runners knowing VO2 max is only one part of the puzzle and this is where understanding the runners efficiency or Running economy becomes more important.
The Significance of Running Economy:
While VO2 max provides insights into aerobic capacity, it is the concept of running economy that often differentiates runners as distances increase. Running economy refers to the efficiency with which a runner utilises oxygen while maintaining a given running velocity. In simpler terms; it represents how much energy is required to cover a specific distance at a specific pace. If we know the runners VO2 max we can then determine the fractional utilisation (percentage of their max) they need to run a given velocity and this can give us runners with similar VO2 max values but vastly different performances over longer endurance events.
To establish running economy we use a slightly different test where the runner has to run for 3-4 minute steps as this gives sufficient time for the oxygen usage to plateau during each step allowing us to measure the amount of oxygen needed for the runner to run at each velocity.
To help highlight a runners efficiency we can also plot a graph to track the metabolic demand of running a particular pace using the ACSM equation which is VO2= (0.2 · Speed) + (0.9 · Speed · Grade) + 3.5 which can give us an estimated amount of oxygen that is needed to run at a given pace.
Unveiling the Differences: Exploring the Three Runners' Data:
Let's examine the data of our three remarkable runners, each possessing their own set of physiological attributes and running economy:
Runner 1:
|
VO2 max: 68.1 ml O2 / kg / min |
| Anaerobic Threshold (AT): 18 km/h (3:20/km) |
| Fractional Utilisation at AT: 76% of VO2 max |
| Aerobic Threshold (AeT):16 km/h (3:45/km) |
| Aerobic Threshold Fractional Utilisation at AeT: 69% of VO2 max |
| Runner Weight: 67.5 kg |
|
Velocity (km/h) |
Oxygen consumption (ml O2 / kg /min) |
Running Economy (ml O2 / Kg / Km) |
| 14 | 40.96 | 176 |
| 15 | 43.11 | 172 |
| 16 | 46.96 | 176 |
| 17 | 51.33 | 181 |
| 18 | 52.00 | 173 |
We can tell from the above data that this runner is very economical in that the amount of oxygen they need to run is relatively low and their running economy is good sitting below 180 ml O2 / kg / km. Anything under 200 ml O2 / kg /km is considered good. This highlights that this particular runner has a good ability to convert the oxygen they consume into mechanical work.
When we plot the oxygen consumption (green line) vs the theoretical oxygen demand (red line) at each of the test velocities we get the below graph.
The above graph confirms that this particular runner has good running efficiency in that they amount of oxygen they actually need to run at each of the velocities is lower than the oxygen demand.
Runner 2:
|
VO2 max: 67.8 ml O2 / kg / min |
| Anaerobic Threshold (AT): 17 km/h (3:31/km) |
| Fractional Utilisation at AT: 89% of VO2 max |
| Aerobic Threshold (AeT):15 km/h (4:00/km) |
| Aerobic Threshold Fractional Utilisation at AeT: 80% of VO2 max |
| Runner Weight: 76.5 Kg |
While Runner 2 is a heavier runner, they have a very similar VO2 max value to runner 1 and their velocity at the Anaerobic Threshold is slightly slower but with a much higher fractional utilisation than runner 1 at the Anaerobic Threshold, meaning that they are using a lot more of their aerobic capacity to maintain the pace (which will likely mean their ability to maintain their threshold pace is less), we also see a slightly slower Aerobic Threshold pace coupled with a higher fractional utilisation compared to runner 1.
| Velocity (km/h) | Oxygen consumption (ml O2 / kg /min) | Running Economy (ml O2 / Kg / Km) |
| 14 | 43.86 | 188 |
| 15 | 56.38 | 226 |
| 16 | 59.00 | 221 |
| 17 | 60.43 | 213 |
| 18 | 60.77 | 203 |
We can start to see some of the differences between runner 1 and runner 2 if we compare the oxygen consumption and that all velocities tested they are using a much higher amount of oxygen (hence the higher fractional utilisation) this also correlates to a slightly worse running economy. Although it should be noted they are still a relatively efficient runner, they are less efficient than runner 1.
We can see that the above graph differs from the first runner in that the oxygen uptake closely matches the calculated oxygen demand. This ties in with the running economy data in that this runner, while able to meet the oxygen demand at each of the velocities we start to see it decouple at 17km/h which is an indicator that they have reached their Anaerobic Threshold and that more of the energy needed is coming from Anaerobic systems.
Runner 3:
|
VO2 max: 65.6 ml O2 / kg / min |
| Anaerobic Threshold (AT): 13 km/h (4:37/km) |
| Fractional Utilisation at AT: 85% of VO2 max |
| Aerobic Threshold (AeT):10 km/h (6:00/km) |
| Aerobic Threshold Fractional Utilisation at AeT: 55% of VO2 max |
| Runner Weight: 71.2 Kg |
The first 2 runners are both high level runners, runner 3 is also a good runner but is at quite a different level compared to the previous 2. By looking at running economy we can investigate why this is as runner 3 has a relatively high VO2 max and not dramatically different compared with the other 2 runners, meaning they have a relatively good engine but their ability to run faster is not quite as good.
When we take into account their running economy we can start to see why this is the case:
| Velocity (km/h) | Oxygen consumption (ml O2 / kg /min) | Running Economy (ml O2 / Kg / Km) |
| 9 | 36 | 240 |
| 10 | 45 | 271 |
| 11 | 49 | 267 |
| 12 | 51 | 256 |
| 13 | 56 | 258 |
As you can see from the above table, the Oxygen being used at much lower velocities is quite high. To compare, at 10km/h (6min/km) they are using 45 ml of Oxygen per kg per minute where as runner 1 is capable of running close to 16km/h (3:45/km) for about the same amount of oxygen and runner 2 can run ~14km/h (4:17/km) for 45ml of oxygen per kg / min.
If we compare the running economy of runner 3 we can see that this runner is significantly less efficient in that they need a lot more oxygen to run at a much slower velocity than the other 2 runners despite having a similar sized engine. Basically highlighting that even through they are capable of taking in a large amount of oxygen they are not very efficient at converting this into mechanical work.
If we plot this runners oxygen consumption vs demand we get a totally different looking graph:
As we can see from the above graph, the actual oxygen consumption is higher than the theoretical oxygen demand. This confirms the running economy data in that this particular runner is using a lot more oxygen to run each of the tested velocities than what is theoretically needed, meaning they are wasting a lot of energy when they run.
What factors influence running economy?
There’s a lot of various factors that make up running economy, some genetically determined others are influenced by environment and training.
Muscle fibre composition: Runners with a higher percentage of ‘slow-twitch’ (Type I) muscle fibres tend to have been running economy as these muscles are optimised for working aerobically and tend to require less overall energy to contract. Runners who have higher percentages of ‘fast-twitch’ (Type II and Type IIx) muscle fibres tend to have lower running economy as these muscles are great at generating higher levels of power but tend to rely more heavily on energy from the glycolytic system.
Joint flexibility: Conversely to many people for running economy is often better in runners who have slightly stiffer joints. As, stiffer joints require less energy to stabilise and contract often returning more elastic recoil. This is why carbon plated shoes are helping runners to improve their running as the carbon plate offers additional stiffness and allows the runner to return more of that elastic energy to the ground.
Training: The type of training a runner has done previously and for how long they have been training is one of the biggest factors that influence running economy and the main area we have influence over. Running consistently over a number of months and years is the absolute best method for improving running economy, by consistently running the body adapts and will naturally find ways to become more efficient. However, including strength work (plyometrics, hill reps, weights etc) can have huge benefit for runners looking to improve their running economy.
Unlocking the Potential: Tailored Advice for Each Runner:
Runner 1 is unlikely to see significant improvements in running economy and not a factor they should focus too heavily on. This particular runner would likely be best allocating some focus on bringing their ability to run faster at their Thresholds. As they are currently using less oxygen at these physiological points it is likely that they can increase them over time to become a faster runner and improve their ability to sustain higher velocities for longer.
Runner 2 will likely benefit from focusing a bit more on aerobic endurance and working on reducing the cost of running at their anaerobic threshold. Likely working on some running form improvements and some plyometrics will improve this runners running economy and should be capable of closing the gap to runner 1.
Runner 3 need to prioritise running economy and working to become more efficient, they have a very strong engine but their efficiency is the key thing holding them back. To improve this it is likely building up the running volume gradually and consistently doing longer aerobic endurance training, with that, this runner should be cautious about doing too much high intensity running initially as this will likely reduce their ability to become more efficient.
Conclusion:
The intricate relationship between VO2 max and running economy unveils the secrets behind endurance running. While VO2 max sets the foundation for aerobic capacity, it is running economy that ultimately separates runners as distances increase. By understanding the significance of running economy and analysing the unique data of our three runners, we gain valuable insights into their distinct physiological profiles and avenues for improvement.
Which runner do you think is most like you? Leave us a comment below.