Running Economy: A Comprehensive Review

Running Economy: The Forgotten Factor in Elite Performance

Running performance is a complex interplay of several physiological factors. These include a high maximal oxygen uptake ($VO<em>{2max}$), the ability to sustain a high percentage of $VO</em>{2max}$ for extended periods (fractional utilization of $VO<em>{2max}$), and the capacity for efficient movement, known as running economy (RE). While $VO</em>{2max}$ and fractional utilization have been extensively studied, running economy has received relatively less scientific attention since the 1970s.

Running economy is typically measured as the steady-state oxygen uptake ($VO<em>2$) at exercise intensities below the ventilatory threshold. Standard assessment methods involve extrapolating $VO</em>2$ to a common running speed, such as $268 ext{ m/min}$, or determining the $VO_2$ required to cover one kilometer. The importance of running economy has increased, particularly with the rise of East African runners to dominance in long-distance events over the last two decades, as performance differences among elite athletes are often highly correlated with variations in economy.

For an athlete to achieve world-class running performance, their $VO<em>{2max}$ must generally exceed $70 ext{ mL/min/kg}$, with average values for established world-class runners typically falling between $75-80 ext{ mL/min/kg}$. The ability to sustain a high percentage of $VO</em>{2max}$ is also critical; for marathon runners (events lasting slightly over $2$ hours), this percentage is usually between 80-90 ext{%}, while for a $10 ext{km}$ race (approximately $28$ minutes), it is 90-95 ext{%}. Among elite athletes who possess similarly high $VO_{2max}$ values and fractional utilization capabilities, the athlete with the superior running economy is often the winner.

Differences in Running Economy

A standard approach to measuring running economy involves athletes running at progressively increasing speeds in stages, each lasting $4-10$ minutes—sufficient time to achieve a physiological steady state. The intensity must remain below the ventilatory threshold to avoid the slow component of oxygen uptake, which would prevent steady-state conditions. These treadmill runs are often performed with a \approx1 ext{%} gradient to simulate outdoor wind resistance. Ideally, to account for full wind resistance, surface characteristics, and minor terrain undulations, these measurements would be performed outdoors using portable heart rate telemetry and metabolic systems.

Running economy can be quantified in various ways. Commonly, $VO<em>2$ is interpolated or extrapolated to a reference velocity, with $268 ext{ m/min}$ ($4.47 ext{ m/s}$ or $6 ext{ minutes per mile}$ or $3 ext{ minutes } 44 ext{ seconds per kilometer}$) being the most frequently used. One notable observation is a reported $VO</em>2$ of $39.0 ext{ mL/min/kg}$ at $268 ext{ m/min}$ in an East African runner who achieved a $1500 ext{m}$ time of $3:35$ with a relatively low $VO<em>{2max}$ of $63 ext{ mL/min/kg}$. An alternative, conceptually appealing method, primarily used in Scandinavia, expresses the aerobic requirement as $VO</em>2/ ext{kg}^{-0.75}$. Another standard is the $VO_2$ required to cover one kilometer.

Representative values for the aerobic cost of running across different populations (assuming a \approx1 ext{%} treadmill grade) illustrate these differences:

• Table I: Aerobic Cost of Running (VO~2~)

  • ACSM Reference ($80 ext{kg}$): $58 ext{ mL/min/kg}$ / $175 ext{ mL/min/kg}^{0.75}$

  • Elite Europeans/North Americans ($65 ext{kg}$): $55 ext{ mL/min/kg}$ / $156 ext{ mL/min/kg}^{0.75}$

  • Elite East Africans ($60 ext{kg}$): $50 ext{ mL/min/kg}$ / $130 ext{ mL/min/kg}^{0.75}$

• Table II: Running Economy (VO~2~ required to run 1km)

  • ACSM Reference: $218 ext{ mL/kg/km}$

  • Elite Europeans/North Americans: $210 ext{ mL/kg/km}$

  • Elite East Africans: $187 ext{ mL/kg/km}$

These tables demonstrate that elite East African runners tend to have lower $VO_2$ values across different expressions of running economy, indicating greater efficiency.

Anatomical Basis of Differences in Running Economy

Distance runners are typically small individuals, and the East African runners who dominate elite competition are often even smaller than other distance runners. This smaller body size, particularly thinner lower legs, is thought to be a significant contributor to their exceptional running economy, based on biomechanical principles and experimental data. Studies have shown a significant inverse correlation between maximal calf circumference and the $VO_2$ required to maintain a fixed running velocity ($21 ext{ km/h}$). This relationship is observed not only in East African runners but also within groups of European runners, suggesting that running economy is broadly related to body dimensions, rather than being uniquely associated with 'African' origin.

For example, European runners of particularly small stature, such as the 1972 Olympic marathon champion Frank Shorter, have also demonstrated superior running economy comparable to that of East Africans. This points to the idea that extraordinary running economy may primarily be a characteristic of small individuals, especially those with thin lower legs. This makes intuitive sense, as adding weight, particularly at the distal end of a long lever (like the lower leg, or even in running shoes), significantly increases the energy cost of movement.

Improving Running Economy

Despite the clear importance of running economy to performance, there are surprisingly few studies exploring effective strategies for its improvement. However, several interventions have shown promise:

• Strength and Plyometric Training: These methods potentially improve running economy by either enhancing the stretch-shortening cycle characteristics of muscles or by increasing the stiffness of the muscle-tendon system.

• Altitude Exposure: Studies on altitude exposure show mixed results. There is some evidence suggesting that simply residing at altitude, even without specific training, can improve running economy, although the underlying mechanism is not yet clear.

• Training in the Heat: This strategy also shows potential for improving running economy, but a common mechanistic link across these varied approaches remains elusive.

• High-Intensity Running: This appears to be a common and effective element.

  • Billat et al. (1999) reported improvements in running economy when high-intensity training was incorporated twice weekly into baseline running programs. However, these benefits were diminished or lost if high-intensity training was performed too frequently.

  • Conley et al. (1981) observed improved running economy after high-intensity interval training was added to an athlete's regular mileage.

The rationale behind high-intensity training improving running economy in already well-trained athletes is that if further adaptation in $VO_{2max}$ is limited, the only way to make a demanding task easier (e.g., maintaining a high pace) is to become more efficient. A similar argument applies to altitude training, where a limited aerobic capacity necessitates increased efficiency to sustain performance. Early observations of East African runners often noted their training was conducted at relatively high intensities. This suggests that for athletes training at altitude, high-intensity efforts could naturally lead to improvements in running economy, although this hypothesis requires further experimental verification.

Conclusions

Running economy is unequivocally important for running performance. Even among highly trained runners, there is a considerable range in economy. While runners of East African origin tend to exhibit superior economy, this appears to be largely a function of their smaller overall size and slender lower limbs, rather than an inherent 'African' genetic trait. Evidence suggests that integrating high-intensity interval training into a runner's regimen can improve running economy. Other factors like plyometric training, altitude exposure, and heat exposure may also contribute to improvements, though their precise mechanisms are still being investigated. For elite athletes who have already maximized their $VO_{2max}$ and their ability to sustain high percentages of it, future advancements in running performance are likely to depend significantly on enhancing running economy.

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