Rucking

• Make walking harder, so it burns more energy and challenges the heart more, without running.
• Strengthen the legs, hips, back and trunk by carrying a load.
• Load the skeleton with more weight on each step.
• Build the capacity to carry things, a practical skill for hiking, work and later life.
• Get people outdoors and walking more often.

Carrying loads on foot is as old as armies. A review of soldier load carriage found that foot soldiers seldom carried more than 15 kg before the 18th century, and loads have risen steadily since as weapons and protective gear got heavier [1]. The US Army still tests it: candidates for the Expert Infantryman Badge must complete a 12-mile foot march in 3 hours or less wearing a 35-pound ruck.

The civilian version is gentler. Jason McCarthy, a former Green Beret, co-founded the pack maker GORUCK with his wife Emily in 2008, and its events and training guides spread the word. Writers such as Michael Easter and physicians such as Peter Attia now promote it as a way to make walking harder without running.

What sets rucking apart from hiking with a daypack is intent. The load is chosen as a training stimulus, it is increased over time, and the walk is done at a brisk, steady pace. Rucking is not the same as rucking in rugby, the contest for the ball after a tackle, which accounts for many of the searches for the word.

There is no trial that sets the right load for health, so the numbers come from military practice and coaching experience:

For a 180 lb (82 kg) person, 10% is about 18 lb (8 kg), 20% about 36 lb (16 kg) and one third about 60 lb (27 kg).

Heavier is not automatically better. Military data tie heavier loads to more injuries and faster fatigue [13][14], and a meta-analysis of foot marches found that strength, power and balance all drop right after a loaded march [15]. Many people get more from a moderate load carried farther, uphill, or more often than from a heavy load carried a short way.

The standard tool for these estimates is the Pandolf equation, which predicts energy cost from body mass, load, speed, grade and terrain [2]. Its load term rises with the square of the load as a fraction of body mass, so each extra kilogram costs a little more than the last. Our chart shows its predictions for an 80 kg walker at 1.34 m/s, close to the most economical walking speed of 1.39 m/s that US Army researchers found across 48 studies [16].

Three caveats keep these numbers honest:

• Predictions are approximate. In infantry soldiers carrying 25 to 70 kg, four of five standard equations underpredicted measured cost, and Pandolf itself was off at slow speeds and very heavy loads [7].
• Light loads on flat ground add little. A CrossFit-style vest of 6 to 9 kg raised physiological demand only when walking up a 10% gradient, not on the flat or at 5% [3].
• Grade and terrain matter more than load. The Pandolf grade and terrain terms multiply the whole carried mass, so at 3 mph a 10% grade roughly doubles the predicted cost of the same walk [2][1].

Where you carry the load changes the cost. Load close to the body's center of mass is cheapest, and each kilogram added at the feet raises energy cost by 7 to 10% [1]. Vests and backpacks differ too: a model built for vests needed its own term [8], and in one small study women lasted longer on a treadmill test with a vest than with a rucksack [17].

A higher calorie burn per walk is not the same as fat loss. No randomized trial has tested rucking for weight loss; food intake decides most of the outcome.

The most direct civilian evidence is thin. In a 10-week program that mixed resistance training with weighted walking, 15 young men raised squat jump force, push-ups and sit-ups and found a 5 km march in a 23 kg vest easier [9]. With no control group and lifting in the mix, it cannot show what the walking alone did.

The best trial points the other way. INVEST in Bone Health randomized 150 older adults with obesity to weight loss alone, weight loss plus a weighted vest worn about 7 hours a day to replace the lost weight, or weight loss plus resistance training [4]. After 12 months:

An older, non-randomized study is more encouraging: 9 postmenopausal women who did weighted vest exercise plus jumping three times a week for 5 years kept their hip bone density, while active controls lost 3.8% at the total hip [11]. The jumping, not the vest alone, may have done the work, since bone responds best to high, fast strains.

If muscle and bone are the goal, strength training has far stronger evidence. Rucking fits best as a way to load walking, alongside lifting rather than instead of it.

Walking itself has strong evidence. In a meta-analysis of 15 cohorts with 47,471 adults, more daily steps went with lower mortality, levelling off at 6,000 to 8,000 steps a day in people over 60 and 8,000 to 10,000 in younger adults [12]. Rucking keeps everything that walking offers and raises the effort of each step.

Compared with running, rucking keeps a walking gait, and a trial of light vests found no change in stride length or frequency [3]. That makes it attractive to people who cannot or do not want to run. It is not a substitute for higher intensity work: if the goal is VO2 max, intervals such as the Norwegian 4x4 push the heart much harder, and for most fit people a loaded walk is steady, moderate work of the kind covered in zone 2 cardio.

Everything we know about rucking injuries comes from soldiers, who carry heavier loads over longer distances than most civilians. In Australian Army records, 404 of 1,954 injuries were attributed to load carriage, mostly to the lower limb and back, and muscular stress caused more than half [5]. Women and men had similar injury rates, with the back the most common site for both [18]. Reviews list blisters, metatarsalgia, stress fractures, knee pain and low back problems as the usual problems [14][13].

Rucksack palsy

Shoulder straps can stretch or compress the brachial plexus, the nerve bundle that runs to the arm, causing numbness, tingling and weakness. This rucksack palsy is more likely with heavier loads and longer distances, and hip belts, wider padded straps and lighter, balanced loads reduce it [6]. A case series described three soldiers with isolated nerve injuries, including to the long thoracic nerve that holds the shoulder blade in place [19]. Numbness or weakness in the arm during or after a ruck is a reason to stop and get checked.

Fatigue and balance

A loaded march leaves you weaker and less steady for a while: lower-body strength, trunk strength, power and postural stability all fall straight after [15]. That matters on downhill sections and rough trails, where most falls happen.

Load placement is the one variable with clear physiology behind it. Weight close to the body's center of mass costs the least energy and keeps posture closest to normal walking [1]. Use a dedicated weight plate or sandbags that do not shift, rather than loose dumbbells.

Hip belts are about comfort and shoulder relief, not efficiency. A belt reduces pressure on the shoulders [1], but in a crossover study with a pack at 30% of body mass, fastening the hip strap did not change oxygen cost or blood pressure [20].

People adapt to load remarkably well with practice. Nepalese porters carry 100 to 200% of their body weight on mountain paths at a lower metabolic cost than other groups who carry much less [21]. That adaptation took years; the safe civilian path is weeks to months of gradual progression.

A practical progression:

1. Weeks 1 to 2: an empty pack on your usual walking route, 20 to 30 minutes.
2. Then about 10% of body weight on flat routes, 2 to 3 times a week.
3. Add distance first, then hills, then about 5 lb at a time.
4. Stay below one third of body weight and keep at least a day between hard rucks.

• Starting with a heavy load because the walking feels easy.
• Adding load and distance in the same week.
• Loose weights that sit low and bounce, which strain the lower back and shoulders.
• Thin straps that dig into the shoulders, the setting for rucksack palsy.
• New or worn-out shoes and cotton socks, which cause blisters.
• Ankle weights, which raise energy cost the most per kilogram.
• Treating rucking as a replacement for lifting or for harder cardio.

• have back, hip, knee or foot pain, or a recent injury in those areas
• have shoulder problems, tendinitis or nerve symptoms in the arms
• have osteoporosis with fractures, or poor balance
• are pregnant
• have heart or lung disease, or high blood pressure that is not controlled

• Blisters and foot pain, the most common load carriage problems.
• Knee pain, especially on long downhills.
• Low back strain from heavy or poorly placed loads.
• Rucksack palsy: numbness, tingling or weakness in the arm from strap pressure.
• Stress fractures in the feet or shins when load and distance rise too fast.
• Temporary loss of leg strength and balance after long, heavy rucks.