Rucking: The Fitness Trend, Evidence-Checked

Rucking sounds almost too simple for a fitness trend:

Make your backpack heavier and go for a walk.

That simplicity is exactly the appeal. You need no ergometer, no track and hardly any technique. At the same time, ordinary walking gets considerably harder.

But many claims around rucking go further:

• 40–60 % more calories than walking
• automatically zone 2
• hardly any interference with strength training
• good for bone density
• gentler than running
• safe under 30 % of body weight

Some of that is plausible. Some is stated too precisely for the data.

The most important context first: most research on rucking does not come from the fitness world but from military load carriage.

That makes it useful — but not transferable 1:1.

What is rucking, scientifically speaking?

In studies the topic usually runs under load carriage: walking or marching with additional load, frequently in a backpack.

The demand changes through several factors at once:

• weight of the load
• body weight
• walking speed
• gradient
• surface
• position of the load
• duration
• training status

So even the question “how demanding is rucking?” can hardly be answered sensibly without those details.

15 kg on flat asphalt at 4 km/h is different training from 15 kg on a steep trail at 6 km/h.

More load raises energy expenditure — but not by a fixed percentage

The basic idea is well established: the more load you move while walking, the higher the metabolic cost generally becomes.

Classic load-carriage models like the Pandolf equation try to estimate that expenditure from body weight, load, speed, gradient and terrain.

Experimental studies also show a clear trend.

Quesada et al. had participants march with 0, 15 and 30 % of their body weight. As load rose, so did oxygen uptake, heart rate and biomechanical demands.

A study using weighted vests at 10, 15 and 20 % of body weight likewise found higher oxygen uptake and relative training intensity compared with unloaded walking.

What does not follow from that:

20–25 % of body weight always burns exactly 40–60 % more calories.

The relative increase depends too heavily on speed, gradient and the individual.

For practical purposes the more robust statement is enough:

Rucking makes walking metabolically more expensive — and you can steer the intensity through load, pace and terrain.

Does that automatically get you into zone 2?

No.

For a fit, heavy person, ordinary walking can be very easy. Added load can raise heart rate considerably and thereby produce a more useful endurance stimulus.

But a given load guarantees no given zone.

In a study with professional mountain rescue crews, heart rate, oxygen uptake and perceived exertion all rose with both the gradient and with 10, 20, 30 and 40 % of additional load. The combination of gradient and weight was decisive.

In practice that means:

If you want to use rucking as zone 2 training, you steer the actual demand — not the backpack weight alone.

Useful tools are:

• the talk test
• heart rate
• perceived exertion
• a steady pace

If 10 kg on flat ground barely gets you above stroll intensity, you can walk a little faster or choose a slight incline.

If you can barely speak at 15 kg, the answer is not automatically more weight.

Is rucking gentler than running?

Here plausibility often gets turned into an established claim.

Rucking has no flight phase like running and can therefore feel more comfortable for some people. At the same time, added load increases the forces and moments at hip, knee and ankle and changes trunk posture.

With increasing load, load-carriage studies show among other things:

• higher ground reaction forces
• greater knee and hip moments
• more muscle activity in the lower extremity
• more forward lean of the trunk

So rucking is not simply “joint-friendly running”.

It is loaded walking with its own demand profile.

Whether it is more tolerable than running for you is an individual question.

What the military research says about injuries

Military load carriers often move 30–50 % of their body weight or more, over long distances, under time pressure and on demanding terrain.

Under those conditions, complaints and injuries frequently occur in the:

• feet
• lower legs
• knees
• lower back
• shoulders and neck

Knapik and colleagues describe load, march distance, speed, training status and equipment as relevant influencing factors.

Important for fitness rucking:

That data does not establish a hard “30 % threshold” below which rucking is safe and above which it is dangerous.

It shows a dose concept instead: the higher the load and volume, the more important adaptation, technique, equipment and recovery become.

For recreational sport there is little reason to push straight into ranges derived from military requirements.

How heavy should you start?

Here a practical recommendation makes more sense than a supposedly scientific threshold.

For beginners

• Load: around 5–10 % of body weight
• Duration: 20–30 minutes
• Frequency: 1–2× per week
• Terrain: flat and predictable at first
• Intensity: such that walking stays technically normal

At 80 kg body weight that would be roughly 4–8 kg of added load.

That sounds less spectacular than “start with 20 kg”. Which is exactly the point.

Your feet, shoulders and back have to adapt not only cardiovascularly but also mechanically to repeated load carriage.

Progression: longer first, then heavier

A simple order:

1. Consistency

Tolerate the same light load for two weeks without complaints.

2. Duration

Increase from 20 to 30, later 40 minutes.

3. Pace or a slight incline

Before adding weight substantially, you can raise the metabolic demand through speed or terrain.

4. Load

Increase weight in small steps and then hold it steady for a few sessions again.

This order is not an official rucking standard. It is a conservative training heuristic that stops several loading variables from exploding at once.

Rucking and strength training: do they fit together?

Probably yes — if you assess the load honestly.

What we do not have are good long-term studies directly comparing:

Strength training + rucking versus strength training + running versus strength training + cycling.

So the claim “rucking has hardly any interference” is too strong.

What we do know: concurrent training can generally be combined well with strength training. Newer meta-analyses find no relevant general disadvantage on average for maximal strength or whole-muscle hypertrophy.

Rucking does, however, produce additional local loading for:

• quadriceps
• calves
• feet
• hips
• trunk
• shoulders/traps

If you squat or deadlift heavy the next day, exactly that local fatigue can matter.

So do not treat rucking as “free steps”.

Where rucking fits in the training week

For strength athletes, the following often work:

• after an upper-body day
• on a separate easy conditioning day
• with enough distance from very heavy lower-body sessions

If you are training for HYROX, rucking can complement general endurance and load tolerance. But it does not replace race-specific work on sleds, lunges, farmers carries or compromised running.

Specificity remains specificity.

What about bone health?

Added load increases the mechanical demand on the skeleton. From that it is plausible to infer that rucking provides a different stimulus for bone than cycling does.

But direct high-quality studies showing that fitness rucking reliably improves bone density in civilians are limited.

So the clean formulation is:

Rucking is weight-bearing activity with a higher mechanical load than ordinary walking — a specific bone density benefit is plausible but not as well directly established as often presented.

Equipment: more important than the trend suggests

The heavier the load, the more important a backpack that holds it stably against your body becomes.

Sensible features are:

• the load close to your back
• no weight swinging loose
• wide, well-fitting shoulder straps
• at higher loads, possibly a useful hip belt
• shoes and socks you already tolerate over longer distances

Military reviews show that load distribution and backpack design can influence muscle activity and complaints.

So you do not immediately need a specialist backpack for 300 euros — but a thin everyday backpack with a loose weight plate in it is not a particularly good solution as the load rises.

The most common mistakes

Starting too heavy

Heart and lungs can feel ready while your feet and shoulders are not yet used to the load.

Chasing weight rather than a training stimulus

20 kg in the backpack is not a performance goal in itself.

If 8 kg at a higher pace already produces the endurance stimulus you want, you do not have to go heavier on principle.

Underestimating downhill

A descent can change the mechanical demand and quickly becomes unpleasant with a heavy pack. Difficult terrain should be its own progression variable.

Counting rucking as strength training

Rucking trains load carriage — but it does not replace systematic squat, pull or press progression.

Logging rucking

In hitPR, rucking can be logged as a custom exercise with “distance + time”. You can additionally note the backpack weight in the notes.

What is interesting above all is the combination with your strength data: if distance, pace or load in rucking rise while the per-exercise trend charts stay stable on squats and deadlifts, the load is probably fitting well into your overall system.

If both get worse at the same time, that is no proof against rucking — but it is a reason to review volume and placement.

Conclusion

Rucking is neither a miracle cure nor nonsense.

The solid statement is:

Added load makes walking more demanding metabolically and mechanically.

How large that effect is depends on weight, pace, gradient, terrain and the individual. Which is exactly why blanket claims like “60 % more calories” or “safe under 30 % of body weight” are worse than progressive load management.

For strength athletes, rucking can be an attractive conditioning option — especially when ordinary walking is too easy and running is not wanted.

Start conservatively, increase one variable at a time, and treat the session like training.

Because that is what it is.

Sources

• Pandolf KB, Givoni B, Goldman RF (1977). Predicting Energy Expenditure with Loads While Standing or Walking Very Slowly. Journal of Applied Physiology, 43(4):577-581.
• Knapik JJ, Reynolds KL, Harman E (2004). Soldier Load Carriage: Historical, Physiological, Biomechanical, and Medical Aspects. Military Medicine, 169(1):45-56.
• Knapik JJ et al. (2012). A Systematic Review of the Effects of Physical Training on Load Carriage Performance. Journal of Strength and Conditioning Research.
• Quesada PM et al. (2000). Biomechanical and Metabolic Effects of Varying Backpack Loading on Simulated Marching. Ergonomics, 43(3):293-309.
• Puthoff ML et al. (2006). The Effect of Weighted Vest Walking on Metabolic Responses and Ground Reaction Forces. Medicine & Science in Sports & Exercise.
• Grenier JG et al. (2012). Energy Cost and Mechanical Work of Walking During Load Carriage in Soldiers. Medicine & Science in Sports & Exercise, 44(6):1131-1140.
• Pinedo-Jauregi A et al. (2022). Physiological Stress in Flat and Uphill Walking with Different Backpack Loads in Professional Mountain Rescue Crews. Applied Ergonomics, 103:103784.
• Schumann M et al. (2022). Compatibility of Concurrent Aerobic and Strength Training for Skeletal Muscle Size and Function. Sports Medicine, 52(3):601-612.