12-3-30 vs running: what pace it is really worth

The answer, model by model

12-3-30 is a walk at a 12% incline and 4.8 km/h (3 mph) for 30 minutes. The table gives the flat running speed that costs the same energy per minute, according to two published models.

Sources: Minetti et al., Journal of Applied Physiology, 2002 ↗ · ACSM metabolic calculations (Texas Tech University) ↗

How the two calculations work

Each model gives the cost of walking on the slope and the cost of running on the flat. The equivalent speed is the one at which running on the flat needs the same energy per minute.

1. 01

   Minetti: cost times speed

   Minetti’s fitted curves give the net cost of walking on a 12% slope as 5.46 J per kg per meter. At 1.33 m/s (4.8 km/h), that is 7.3 W per kg. The same curves put flat running at 3.6 J per kg per meter, so 7.3 W per kg buys a flat run at 2.02 m/s, or 7.3 km/h.

2. 02

   ACSM: oxygen uptake

   The ACSM walking equation is VO₂ = 0.1 × v + 1.8 × v × grade + 3.5, in mL/kg/min with v in meters per minute. At 80 m/min and a 0.12 grade, it gives 28.8, or 8.2 METs. The ACSM running equation on the flat, VO₂ = 0.2 × v + 3.5, reaches 28.8 at 126 m/min, or 7.6 km/h.

3. 03

   Compare the two

   The two land about 4% apart at 12%. The ratio between a walk and a run is the robust result; the absolute energy figures are less so, as the next section shows.

Calories: a range, not a number

For a 70 kg adult over 30 minutes, Minetti’s net cost gives about 220 kcal. The ACSM oxygen uptake, at about 5 kcal per liter of oxygen, gives about 300 kcal gross, or about 265 kcal net once resting metabolism (about 37 kcal in 30 minutes) is removed.

The models differ by about 20% on energy while agreeing within 4% on the running equivalent, because each scales the cost of walking and the cost of running together. Treat the running equivalent as the firm result and the calories as a range from 220 to 265 net. Both are population averages: in Minetti’s 10 runners, the minimum walking cost had a standard deviation of about 30% of its mean.

What 3 mph is worth at other inclines

The equivalence is most meaningful above about 6 km/h of flat running speed, which at this walking speed starts near a 9% incline. At the low end the models drift apart: on the flat, Minetti gives 3.3 km/h and ACSM 2.4 km/h. From 8% to 15%, they agree within 5%.

The Runkyz Incline walking plan in running terms

The four weekly stages of the plan raise the incline, the speed and the duration together. Their flat running equivalents climb from about 4.8 km/h in week 1 to 7.3 to 7.6 km/h in week 4.

What this does not tell you

Equal energy per minute does not mean an equal training effect, and the figures assume the hands are off the rails.

• Handrails change the cost. In 13 healthy adults at a 10% incline, energy expenditure was 8.83 kcal/min without support, 7.77 holding the rails upright and 6.02 holding them while leaning back, close to the 6.32 of a 5% incline without support.
• A walk has no flight phase and no running impact, and the trainers Healthline interviewed still warn that a steep incline is very taxing, especially with muscle or joint conditions.
• Both models are averages measured on healthy adults, at steady state. Your own cost can differ.

Sources: Hofmann et al., International Journal of Exercise Science, 2014 ↗ · Healthline — What experts think of 12-3-30 ↗

How Runkyz uses the same curves

Runkyz converts between incline and belt speed with Minetti’s curves. When your treadmill cannot reach the incline a session asks for, the game keeps to the maximum incline you entered and raises the walking speed to match the effort. That is an approximation, not the same workout.

The 12-3-30 session in the game is the walk described above, with a build-up plan from 8% to 12% in four weeks.