Expert Spotlight
Peter Attia

The Pro Full-Stack test lets us look at efficiency in three distinct ways—each one highlights a different leak in the “oxygen-to-speed” chain.

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1. Metabolic-to-Work efficiency (sometimes called mechanical or metabolic efficiency).

   – Question: How much oxygen do I burn to generate one watt of external work?

   – Calculation: divide total VO₂ (in millilitres per minute) by power output in watts.

   – Benchmarks: elite runners need roughly 15–17 ml O₂ per watt; most recreational runners are closer to 18–20 ml O₂ per watt. A lower value means better fuel economy at the muscular level.

2. Work-to-Speed efficiency (often called performance efficiency or effectiveness in running).

   – Question: How much forward speed do I get for every watt per kilogram I push?

   – Calculation: divide speed in metres per second by power in W kg⁻¹.

   – Benchmarks: sub-3-hour marathoners sit around 0.034–0.035 m s⁻¹ per W kg⁻¹; casual club runners are typically 0.028–0.031. A higher number means each watt moves you faster.

3. Metabolic-to-Speed efficiency (overall running economy).

   – Question: How much oxygen does it cost to hold a given pace?

   – Calculation: divide mass-specific VO₂ (ml kg⁻¹ min⁻¹) by speed (m s⁻¹) and convert to ml kg⁻¹ km⁻¹.

   – Benchmarks: elite marathoners record 180–200 ml kg⁻¹ km⁻¹; many recreational runners are 210–240. Lower is better.

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Because we can look at intensity in different ways we can interpret which link of this chain has the most room for growth.

Does the athlete need to train harder? Is it a form issue? 

Paired with a decent understanding of energy production at different intensities things can start to make a lot of sense.

 

 

A running example

 

• Interval test pace: 3.0 m s⁻¹ (3 min 20 s /km or 5 min 33 s / mile)

• Athlete VO₂: 45 ml kg⁻¹ min⁻¹, body mass 70 kg → 3 150 ml min⁻¹ total

• Power: 245 W

 

Metabolic-to-Work: 3 150 ml min⁻¹ ÷ 245 W = 12.9 ml O₂ W⁻¹ (excellent)

Work-to-Speed: 3.0 m s⁻¹ ÷ (245 W ÷ 70 kg) ≈ 0.034 m s⁻¹ W⁻¹ kg⁻¹ (elite amateur range)

Economy: 45 ml kg⁻¹ min⁻¹ ÷ 3.0 m s⁻¹ × 60 s = 180 ml kg⁻¹ km⁻¹ (elite level)

 

Interpretation: technique is already strong; future gains should come from raising VO₂-max and threshold, not from form tweaks.

 

Cycling and swimming parallels

 

– Cycling: VO₂-Master plus power. Pros often ride at 17–18 ml O₂ W⁻¹; recreational riders above 20 ml O₂ W⁻¹.  

– Swimming: We have sensor that logs form, power stroke rate and distance-per-stroke while VO₂ measures oxygen cost. 

 

Why these numbers matter

 

– If economy is far outside elite norms, simple technique drills, shoe changes or bike-fit tweaks can unlock large speed gains in weeks—much quicker than trying to add, let's say, 5 ml VO₂-max.

– Retesting after a training block shows clear proof of progress; dropping from 210 to 195 ml kg⁻¹ km⁻¹ economy means the form work paid off even if VO₂-max stayed flat.

– When you know all three efficiencies you know where to focus: build aerobic power when economy is good; fix mechanics when economy is poor. One full-stack session removes the guess-work.

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Economy is often overlooked

 

Runners with better running economy simply run much faster at the same VO₂.