Effort
Level-ground pace is a poor predictor of effort on real terrain. Gradient, surface and load each move the energy cost substantially, and they compound.
A published MET value assumes level ground and no load. Real outings rarely offer either, and the corrections are large enough to change the plan.
Vertical work has a clean physical basis. Raising a mass against gravity requires energy equal to mass times gravitational acceleration times height. For a 75 kg person plus 10 kg of pack climbing 500 vertical metres, the mechanical work is roughly 417 kilojoules, or about 100 kcal.
Muscular efficiency for positive work is around 20 to 25 percent, so metabolic cost is four to five times the mechanical work — on the order of 400 to 500 kcal for that climb, on top of the horizontal cost of covering the distance.
A widely used field approximation: roughly 0.5 to 0.6 kcal per kilogram of total mass per 100 metres of ascent. For the example above, 85 kg × 5 × 0.55 gives about 234 kcal — conservative relative to the efficiency-based figure, and useful as a lower bound.
Descent is not free, and the mistake most people make is assuming it is.
Gentle descent genuinely reduces energy cost below level walking — gravity contributes to forward motion and the muscular demand drops. The minimum energy cost occurs at a downhill grade of roughly 10 percent.
Steeper than that, cost rises again. Controlling descent requires eccentric muscular contraction, in which muscle lengthens under tension to absorb energy. Eccentric work has lower metabolic cost per unit of force than concentric work, but on steep ground the forces are large and sustained.
Eccentric loading is also the primary driver of delayed onset muscle soreness and of the microtrauma that accumulates through a long descent. Quadriceps fatigue after a substantial descent is frequently the limiting factor on a long day — and it is the reason accident rates on descent exceed those on ascent.
Ground that deforms under load absorbs energy that would otherwise propel you.
| Surface | Approximate cost multiplier |
|---|---|
| Paved road | 1.0 |
| Firm dirt trail | 1.05–1.1 |
| Gravel | 1.2–1.3 |
| Rough or rocky trail | 1.3–1.5 |
| Soft sand | 1.6–2.1 |
| Fresh snow, unbroken | 1.6–2.5 |
Terrain factors of this kind have been used in military load-carriage models since the 1970s and remain the standard approach. Soft sand roughly doubling the cost of walking is not an exaggeration — it is among the best-replicated findings in the area.
Carried weight raises energy cost, and the increase is more than proportional once load becomes a significant fraction of body mass.
Light loads under about 20 percent of body mass raise cost roughly in proportion to total mass. Beyond that, gait changes, stabilising demand increases, and cost rises faster than the added weight alone predicts.
Placement matters too. Weight carried close to the trunk and high in the pack is cheaper to transport than the same weight low or away from the body's centre of mass. Weight on the feet is the most expensive of all — commonly cited at four to six times the cost of the same mass on the back, which is why boot weight receives disproportionate attention.
A worked example. A 70 kg hiker carries 12 kg over 14 km with 700 m of ascent on a rocky trail.
Horizontal component: 14 km at roughly 6 METs for 3.5 hours gives approximately 1,000 kcal at 82 kg total mass. Vertical component: 82 kg × 7 × 0.55 gives about 316 kcal. Terrain multiplier of 1.35 applied to the horizontal component adds roughly 350 kcal.
Total on the order of 1,650 kcal — against about 1,000 for the naive level-ground MET estimate. The difference is not a rounding error.
Two routes of identical distance can differ by more than fifty percent in energy cost. Distance alone is close to useless as a planning input.
Plan food and water against the corrected figure rather than the distance. Budget time using Naismith with a Langmuir descent correction, then add a margin for the terrain factor. Expect the descent to punish more than the ascent on a long day, and pace the ascent accordingly.
Use the activity equivalence calculator to compare the corrected effort against other activities in your week, and the daylight window calculator to check that the corrected time estimate still fits inside the available light.