Energy cost of a run from distance, weight, terrain and climbing — plus how much carbohydrate that actually uses.
The energy cost of running is close to a fixed amount per kilogram of body weight per kilometre covered, and it changes surprisingly little with speed. A 10K costs a 68 kg runner roughly the same whether it takes 45 minutes or an hour. What speed changes is the rate: run faster and you spend the same total in less time, which is why a hard 10K feels nothing like an easy one despite the similar number.
Climbing is real physical work against gravity and it shows up clearly. Lifting your body a hundred metres costs a fixed amount you cannot pace your way out of, and on a route like a Genting or Broga climb the vertical becomes a meaningful share of the total. Descending returns very little of it, which is a fair description of how quads feel the next morning.
Of the energy you use running, a portion comes from carbohydrate and the rest from fat, and the share tilts towards carbohydrate as you run harder. That matters because carbohydrate is the tank that runs dry, usually somewhere between 90 minutes and two hours of hard effort. The gram figure above is a rough estimate of how much of that tank a run empties, which is a more actionable number than the calorie total.
Running economy varies between individuals by several percent, watches disagree with each other and with laboratories, and no formula knows what your gait costs you. The figure here is useful for comparing this week's long run to last week's, and for sizing what to replace afterwards. It is not precise enough to build eating decisions on, and running usually goes better on more fuel rather than less.
Over the same distance, barely. The energy cost of running is close to a fixed amount per kilogram per kilometre, so a 10K burns about the same whether you take 45 minutes or 65. Running faster burns more per hour simply because you cover more ground in that hour. This is why distance, not pace, is the number that matters in the calculation.
Most watches report gross calories, including what you would have burned anyway just being alive during that time. Some also apply generous assumptions about efficiency. The net figure here strips out resting metabolism, which is the honest number if you are trying to understand the cost of the run itself. Either way, treat any calorie figure as carrying an error of fifteen to twenty percent.
More than people expect. Climbing costs roughly an extra 0.01 kcal per kilogram for every metre of elevation gained, so a 70 kg runner climbing 500 metres pays about 350 extra calories on top of the flat cost of the distance. Descending gives a little back but not much, and it costs your quadriceps instead.
A little. Thermoregulation raises metabolic cost modestly, on the order of a few percent, and your heart rate rises much more than your energy use does. The bigger practical effect of heat is that it slows you down and shortens what you can complete, not that it turns a run into a furnace.
Not on its own, and not day to day. Calorie estimates for running carry a wide error, appetite and recovery are poor at reading arithmetic, and running well generally needs more fuel than people expect rather than less. The more useful thing to take from this page is the carbohydrate figure, which tells you what to replace during and after long sessions.
Because you are carrying it. Energy cost scales almost directly with mass, so a 90 kg runner burns roughly a third more than a 68 kg runner over the same route at the same pace. It is also why the same 10K feels different to two people running side by side.
Turn any distance and finish time into pace per km, pace per mile and speed.
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