Key takeaways
Carrying a load raises the energy cost of walking, more so with heavier packs, faster speeds, hills and soft ground
That extra cost can turn an easy walk into moderate exercise, but evidence that rucking itself raises VO2max in civilians is limited
Start with about 10% of body weight, keep the load high and tight on your back, and increase load or distance gradually
Rucking, walking with a weighted backpack, has moved from military training into mainstream fitness. It is popular on social media and fitness podcasts because it sounds like a shortcut: the accessibility of walking with the effort of something harder. The physiology behind the extra effort is well established. The evidence for VO2max is thinner.
Why a pack makes walking harder
Military scientists have studied load carriage for decades, because soldiers march with heavy kit. In 1977, Pandolf, Givoni and Goldman published an equation that predicts the energy cost of standing and walking with a load. It includes your body mass, the load, walking speed, gradient and a terrain factor for surfaces such as sand, snow or rough tracks. The equation, still widely used, captures what anyone who has carried a heavy pack knows: energy cost rises with each of these.
A 2004 review by Knapik and colleagues summarised the wider research:
- Energy cost rises progressively with heavier loads, higher body mass, faster speeds and steeper slopes.
- Keeping the load close to your centre of mass, high and tight on the back, gives the lowest cost and the most upright posture.
- Weight on the feet is very costly: each kilogram added to the foot raised energy expenditure by 7–10%.
- Regular road marching combined with aerobic and resistance training improved marching speed and efficiency.
Does that raise VO2max?
VO2max improves when training repeatedly asks your heart and muscles for more oxygen than they are used to (see what limits VO2max). Rucking can do that in two ways:
- For beginners and older adults, a loaded walk may be hard enough to count as moderate or even vigorous exercise, without the impact of running. In unfit people, almost any sustained moderate effort raises VO2max.
- Hills and pace matter more than weight alone. A light pack up a slope will usually challenge you more than a heavy one on the flat at a stroll.
The honest caveat: there are few controlled trials of rucking for VO2max in the general population. Most of the data come from soldiers, who also run, lift and march. For people who are already fit, a pack rarely pushes heart rate as high as running or intervals, which remain the stronger stimulus (see HIIT vs steady cardio). Think of rucking as a way to make aerobic base work harder and more varied, not as a replacement for intensity.
How it compares
| Activity | Typical intensity | Impact on joints | Main benefit | Main drawback |
|---|---|---|---|---|
| Walking | Light to moderate | Low | Easy to do daily, builds a base | Small VO2max stimulus for fit people |
| Rucking (flat) | Moderate | Low to moderate, more load on back and feet | Harder walk, trunk and leg endurance | Back, foot and knee strain if overdone |
| Rucking (hills) | Moderate to vigorous | Moderate | Higher heart rate without running | Downhills are hard on knees |
| Running | Moderate to vigorous | Higher impact per step | Strongest of the three for VO2max | More impact, higher skill and fitness needed |
If you want walking intervals without a pack, Japanese interval walking is better researched. Runners can use rucking as low-impact extra volume alongside running.
How to start and progress
- Start light: about 10% of body weight in a well-fitted backpack, on flat ground, for 20–30 minutes.
- Pack it well: put the weight high and close to your back, tighten the straps, and use a hip belt if your pack has one. Knapik's review notes that hip belts reduce pressure on the shoulders.
- Change one thing at a time: add distance, then hills, then load. Small weekly increases are safer than big jumps.
- Watch intensity, not just weight: aim for brisk effort where talking is possible but not easy, similar to the top of zone 2.
- Frequency: one or two rucks a week, on non-consecutive days, alongside normal walking and some strength training.
- Don't run with the pack. Loaded running sharply raises impact and injury risk.
Rucking also suits event preparation: HYROX involves carries and sandbag lunges, and hikers carry packs anyway. Check whether your fitness improves with the VO2max calculator or fitness age calculator, and see how to improve VO2max for a full plan.
Injury risk
In Knapik's review, common problems with prolonged load carriage were foot blisters, stress fractures, back strains, metatarsalgia (pain in the ball of the foot), rucksack palsy (nerve compression from shoulder straps) and knee pain. These came mostly from soldiers carrying far heavier loads than most recreational ruckers, but the lesson holds: load and volume should rise slowly. In a survey of 593 US soldiers after a 12-month deployment to Afghanistan, the heaviest load worn was one of several factors linked to injury.
Safety: if you have back, hip, knee or foot problems, osteoporosis, heart disease or high blood pressure, ask a doctor or physiotherapist before rucking. Stop if you get sharp pain, numbness or tingling in the arms, or chest pain.
Frequently asked questions
Does rucking improve VO2max?
It can help if it pushes your heart rate higher than ordinary walking, especially for beginners. There is little direct evidence for rucking itself, and running or intervals are a stronger stimulus for fit people.
How heavy should my rucksack be?
A common starting point is about 10% of body weight on flat ground. Increase load, distance or hills one at a time over several weeks.
Is rucking bad for your back or knees?
Military research links heavy, prolonged load carriage to blisters, back strain, knee pain and stress fractures. Light loads, a good pack with a hip belt and gradual progression lower the risk.
Sources
- Pandolf KB, Givoni B, Goldman RF. Predicting energy expenditure with loads while standing or walking very slowly. J Appl Physiol, 1977.
- Knapik JJ, Reynolds KL, Harman E. Soldier load carriage: historical, physiological, biomechanical, and medical aspects. Mil Med, 2004.
- Roy TC, et al. Risk factors for musculoskeletal injuries for soldiers deployed to Afghanistan. Aviat Space Environ Med, 2012.