The 7 capacities every trekker needs
Two people can both say they're "pretty fit" and have completely different treks. Here's why, and what to do about it.
By Nathan Gee, BSc Sports Science · Updated 21 October 2026 · 6 min readFitness isn't one thing
A strong runner can be wrecked by a long descent. Someone who's in the gym four times a week can run out of legs on day three. Both are fit. They're just fit for different things.
A multi-day trek asks a specific set of questions of your body. I break them into seven capacities, because once you can see them separately, it gets much easier to spot the one that's going to cause you trouble.
Same "fitness", different gaps. Two made-up profiles to show the idea, not measured data:
- The runner: a big engine and happy on long days, lighter on strength and carrying a pack.
- The gym regular: strong legs and stable under load, lighter on aerobic base and repeat days.
Most people have one or two obvious gaps. The trick is training those, rather than more of what you're already good at.
The seven capacities, one at a time
Tap through. Each one matches a specific thing the mountain will ask of you.
1. Aerobic base
The engine.
Your ability to keep moving for hours without fighting your breathing. It's built slowly, at an easy pace, and it's the one most people try to rush. If you can't hold a conversation, you're probably working harder than this job needs.
- What a gap feels likeBreathless on gentle climbs
- How to train itEasy, long sessions at talk-test pace
- Common mistakeTraining too hard, too often
2. Time on feet
Comfortable through long days.
Six hours of walking, with food stops and breaks, is a different animal from a one-hour workout. Your feet, hips and shoulders need practice at simply being out there that long.
- What a gap feels likeFine for two hours, then it falls apart
- How to train itA weekly long walk, extended gradually
- Common mistakeOnly ever doing short sessions
3. Uphill capacity
Keep going on long climbs.
Part power, part patience. Your legs and lungs need to sustain effort on climbs that go on for an hour or more. Start too fast and the climb will let you know about it, usually about twenty minutes in.
- What a gap feels likeLegs burn early on sustained climbs
- How to train itStairs, incline walking, steady hills
- Common mistakeStarting the climb too fast
4. Downhill durability
Control on the way down.
Going down, your muscles work as brakes, lengthening under load. That's a different job from climbing, and it's why plenty of fit people finish a big descent with jelly legs and grumpy knees. Most plans are all uphill. Treks aren't.
- What a gap feels likeFine going up, sore coming down
- How to train itControlled descents, step-downs, slow lowering strength work
- Common mistakeLeaving it out of the plan
5. Strength base
Control, not bodybuilding.
Enough strength to control each step on uneven ground, stay stable under a pack and keep your form when you're tired. You don't need to lift huge weights. You do need to lift something.
- What a gap feels likeWobbly on big or uneven steps
- How to train itSingle-leg work, squats, hinges, core
- Common mistakeOnly training what you already enjoy
6. Pack capacity
Confident under load.
On some treks that's a daypack. If you're carrying your own gear, it's a lot more. Either way, a pack changes how you climb, descend and balance, and buying a nicer one doesn't make you better at carrying it.
- What a gap feels likePosture and balance fall apart with weight
- How to train itProgressive pack carries
- Common mistakeAdding the full load the week before you fly
7. Multi-day durability
Do it again tomorrow.
Day one is rarely the problem. Day four, after three days of climbing and descending, is where it shows. It's built by training on repeat days and treating food, sleep and recovery as part of your fitness, not extras.
- What a gap feels likeFine on day one, flat by day three
- How to train itBack-to-back days, recovery habits
- Common mistakeOne huge day instead of repeat days
Where should you start?
Pick the one that sounds most like you on a long walk.
Five ways people get this wrong
None of these are daft. They're just common, and they're all fixable.
Only doing what you're good at
Runners run, lifters lift, and the gaps stay exactly where they were. Your weakest capacity is usually the one you least enjoy training.
Skipping the descent
Plenty of training plans are all uphill. Treks aren't, and the way down is often what people feel most the next morning.
One big day instead of repeat days
A single huge walk proves you can do one huge walk. Durability comes from doing it again the next day.
Treating the pack as a final-week problem
Load needs time. Add it gradually across your training, not in a panic before you fly.
Assuming fit means ready
General fitness helps a lot. It just doesn't cover all seven, and the mountain tends to find the one it missed.
A guide for each capacity
Start with the guide for your weakest capacity. More in-depth guides are on the way.
- Aerobic baseAerobic pacingRead
- Time on feetMountain Day field guideRead
- Uphill capacityStair trainingRead
- Downhill durabilityThe downhill taxRead
- Strength baseStrength training for hikingRead
- Pack capacityPack trainingRead
- Multi-day durabilityBack-to-back daysRead
Questions people ask
What are the seven capacities?
Aerobic base, time on feet, uphill capacity, downhill durability, strength base, pack capacity and multi-day durability. Together they cover what a multi-day trek asks of your body.
Which capacity should I train first?
Your weakest one. Most people have one or two obvious gaps. Train that capacity a couple of times a week for a few weeks while keeping the rest ticking over, then see how your next long walk feels.
Do I need a gym to train them?
No. Stairs, hills, a backpack and some bodyweight or home strength work cover a lot. A gym makes progressive strength work easier, but it isn't essential.
Is general fitness enough for a trek?
It helps, but it rarely covers everything. A strong runner can struggle on long descents, and someone who lifts can run out of steam on day three. That's why it's worth checking all seven.
The free readiness check scores you across the seven capacities, shows your biggest gap and suggests where to start.
