Does Rucking Build Muscle? The Science Explained

Rucking loads muscles in ways that ordinary walking does not, but it falls short of traditional resistance training when the goal is adding noticeable muscle size. Carrying a weighted pack increases the force demands on your legs, core, and upper back with every step, and over time those demands can improve muscular endurance, preserve lean mass, and produce modest strength gains. Whether that counts as “building muscle” depends on what you mean by the phrase, and the science paints a more nuanced picture than either rucking enthusiasts or gym purists tend to acknowledge.

What Happens to Your Muscles When You Ruck

Walking with a loaded backpack changes the mechanical demands on nearly every muscle group below the neck. Research on military cadets found moderate-to-large increases in knee extension torques during the early part of each stride, along with small-to-moderate increases in ankle plantarflexion torques at push-off, with each incremental jump in pack weight.¹ In plain terms, your quads and calves have to work progressively harder as the pack gets heavier. Hip extension torques also climb at heavier loads, meaning the glutes are recruited more aggressively than during a casual stroll.

The upper body gets involved too, though in a stabilizing role rather than a lifting one. The trapezius muscles fire harder to support the shoulder straps, and the erector spinae along the spine contract to keep you upright against the forward pull of the load. Even in children carrying school backpacks of just four kilograms, researchers have measured changes in muscle activation patterns and postural stability compared to unloaded walking.² Scale that up to an adult carrying 15 to 30 kilograms, and the muscular demand is substantial.

The key distinction, though, is the type of demand. Rucking is a sustained, repetitive, lower-intensity effort. Your muscles contract thousands of times over the course of a march, but each individual contraction is well below your maximum force capacity. That stimulus is excellent for building muscular endurance and aerobic capacity. It is far less effective at triggering the kind of high-tension, high-volume mechanical stress that drives significant muscle fiber growth.

Why Rucking Is Not the Same as Lifting Weights

Muscle hypertrophy, the actual enlargement of muscle fibers, requires a few specific ingredients. The muscle needs to generate forces close to its capacity, sustain enough total work volume, and be pushed through a range of motion that creates stretch under load. Traditional resistance training hits all three: a heavy squat, for instance, demands near-maximal quad contraction through a deep range at the knee. Rucking, by contrast, involves relatively modest force per step, repeated over long durations. The total workload is high, but it is spread across so many repetitions at such low individual intensity that the stimulus looks more like endurance training than strength training to the muscle fiber.

This matters because of how muscles adapt to different types of stress. A systematic review and meta-analysis looking at concurrent aerobic and strength training found that when aerobic training was performed through running rather than cycling, type I (slow-twitch) muscle fiber hypertrophy was actually reduced, with a meaningful negative effect.³ Rucking is essentially loaded running or fast walking, so it sits squarely in the category of impact-based aerobic training that can interfere with muscle fiber growth if it replaces or dominates a training program. Someone who rucks five days a week and never lifts is unlikely to see the kind of muscle development they would get from a structured resistance program.

Where Rucking Actually Shines for Body Composition

If rucking is not great for building new muscle, it turns out to be surprisingly useful for holding on to the muscle you already have, especially during periods of weight loss. Losing fat almost always means losing some lean tissue along with it, but physical activity helps tip the ratio in favor of keeping muscle. Research on weight-loss strategies has found that both endurance-type and resistance-type exercise help preserve muscle mass during a calorie deficit, with resistance exercise also improving strength.⁴ Rucking straddles the line between endurance and resistance work, so it offers some protective benefit for lean mass that plain walking does not.

For people who are relatively untrained, rucking can produce early-stage strength and muscle gains simply because the load represents a new stimulus. If you have been sedentary and start walking with a 10-kilogram pack three times a week, your legs are encountering forces they are not adapted to. In that window, you will likely see improvements in leg strength, calf definition, and postural muscle tone. Those gains taper off as your body adapts, which is why experienced ruckers report a plateau in visible muscle changes even as their endurance keeps improving.

The practical upshot is that rucking is a strong complement to resistance training rather than a replacement for it. It burns more calories than unloaded walking, supports cardiovascular fitness, and keeps muscle tissue metabolically active. Used alongside a lifting program, rucking can improve your overall body composition without sacrificing the hypertrophy stimulus you get from the gym.

Which Muscles Respond Most to Rucking

Not every muscle group gets the same treatment from a loaded march. The muscles that see the biggest demand increases are, roughly in order of impact:

• Quadriceps: They absorb the braking forces of every heel strike and drive knee extension. Heavier loads produce proportionally bigger increases in the torque they generate.
• Glutes: Hip extension torques rise substantially at moderate and heavy loads compared to light ones, making the glutes one of the primary drivers of forward propulsion during rucking.¹
• Calves: Ankle plantarflexion torques increase during push-off as pack weight rises, though the effect is smaller than at the knee or hip.
• Erector spinae and core: The trunk muscles work continuously to stabilize the spine under an offset load. This is isometric work rather than through-range contraction, so it builds endurance and stiffness more than size.
• Trapezius and upper back: Shoulder-strap pressure recruits these muscles, though the degree depends heavily on whether the pack’s weight sits on the shoulders or is transferred to the hips by a hip belt.

The lower body dominates because rucking is fundamentally locomotion. Your arms swing but do not carry the load (unless you are using a front-carry implement like a sandbag, which changes the equation). If your primary goal is upper-body muscle, rucking alone will not get you there.

Rucking and Older Adults

One population for whom rucking, or loaded walking more broadly, shows real muscle-related promise is older adults at risk for age-related muscle loss. A randomized controlled trial looking at Nordic walking with added ankle weights found that the weighted group showed significantly greater improvements in skeletal muscle mass percentage for both total body and lower limbs, along with meaningful gains in grip strength, compared to Nordic walking alone.⁵ The weighted group also improved on a screening score used to flag sarcopenia risk.

This is a different context from a 30-year-old trying to add visible quad size. For an older adult whose baseline activity level is low and whose muscles are already atrophying, the stimulus of loaded walking can be enough to meaningfully shift muscle mass and strength. The bar for a “muscle-building” stimulus is lower when the starting point is further from peak capacity. Rucking with a modest backpack gives older adults a way to add progressive resistance to an activity they can already do safely, which matters in a population where barbell squats may not be realistic.

How Load Placement Changes the Picture

Where you carry the weight matters more than most ruckers realize. Keeping the load close to your body’s center of gravity lowers the metabolic cost and reduces the compensatory muscle activity needed to stay balanced. A review of load carriage research found that a double pack, with half the weight on the front and half on the back, was more energy-efficient than a standard backpack.⁶ Framed packs with hip belts also reduced trapezius muscle activation by shifting the load from the shoulders to the pelvis.

From a muscle-building standpoint, this creates an interesting tension. A poorly fitted pack that rides high on the shoulders demands more stabilizer effort from the upper back and trunk, which technically loads those muscles harder. But it also creates a more injury-prone posture and increases fatigue. A well-fitted pack with a hip belt transfers more of the weight to the legs and pelvis, which is safer and more sustainable for longer marches but slightly reduces the upper-body muscle demand. For most people, the safer, better-fitted option is the right call. If you want to hit your traps and upper back harder, that is what rows and shrugs are for.

How Rucking Changes Your Gait and Why That Matters for Joints

Adding load to your back does not just make your muscles work harder. It also reshapes the way you walk. Research on military load carriage found that increasing carried weight decreased knee range of motion and preferred stride length, while increasing the time spent in double support, the phase where both feet are on the ground.⁷ Essentially, your body shortens its steps and keeps both feet planted longer to improve stability under load. Hip rotation and pelvic tilt also increase as the body compensates for the added mass.

These gait changes are your body’s way of staying safe, but they come with trade-offs. A study of ROTC cadets found that after a ruck march, peak impact force and loading rate increased while ankle strength in both dorsiflexion and plantarflexion decreased, even when the cadets did not report feeling tired.⁸ In other words, the muscles that protect your joints fatigue before you feel fatigued, leaving your ankles and knees to absorb more impact with less muscular cushioning. Over the course of prolonged marches, research on metatarsal bone loading found that as toe flexor muscles fatigued, more stress shifted onto the bones themselves, raising injury risk.⁹

This is the core safety consideration for anyone using rucking as regular exercise: the muscles fatigue in ways you cannot feel, and the joints pick up the slack. Building up load and distance gradually is not just good advice but a biomechanical necessity. A common beginner mistake is treating rucking like hiking with extra scenery and jumping to heavy loads before the musculoskeletal system has adapted.

Do Men and Women Respond Differently

A common assumption is that men and women must ruck differently because of differences in height, weight, and body proportions. The biomechanical evidence, however, suggests the opposite. A study comparing gait mechanics and muscle activation during loaded walking found no significant differences between men and women for any measured parameter, as long as the load was scaled to each person’s body weight.¹⁰ When carrying the same relative load, men and women recruited the same muscles in the same patterns and made the same gait adjustments.

This matters practically because it means programming advice does not need to differ by sex. The same principles apply: start with a load around 10 to 15 percent of your body weight, increase gradually, and let recovery dictate progression. The absolute weight in the pack will differ, but the relative stimulus and the muscle response look the same.

Why Leg Strength Before You Ruck Matters More Than You Think

There is a chicken-and-egg relationship between rucking and leg strength. A critical review of the evidence found that measures of lower-body strength and power predict load carriage performance, while load carriage itself temporarily reduces leg strength and power output.¹¹ People with stronger legs ruck faster and more efficiently, and the ruck itself does not make their legs stronger in the long run the way a squat program would.

For recreational ruckers, this means that the best way to improve your rucking performance, and to protect your joints during rucks, is to build leg strength separately. Squats, lunges, step-ups, and calf raises directly improve the force-producing capacity that rucking draws on. Rucking then becomes a way to apply that strength endurance in a cardiovascular context rather than the primary means of developing it. Thinking of rucking as a “cardio day that also uses your legs” rather than a “leg day that also does cardio” aligns better with what the research shows.

Rucking as an Evolutionary Echo

It is worth noting that carrying loads over distance is deeply wired into human anatomy. Research in evolutionary biomechanics has found that load-carrying ability improved from earlier hominids to Homo ergaster, and that this capacity may have been a driving factor in the evolution of our upright posture and long-distance locomotion efficiency.¹² Our wide pelvis, spring-like Achilles tendons, and large gluteal muscles are, in part, adaptations for carrying things while walking upright.

This helps explain why rucking feels natural in a way that many gym exercises do not. Your body is anatomically designed for this movement pattern. It also explains the pattern of muscle engagement: the glutes, quads, calves, and spinal erectors are the exact muscle groups that evolved under the selective pressure of load carriage. You are not tricking your body into an unfamiliar stimulus when you ruck. You are giving it a version of the stimulus it was built for, just not a version intense enough to push past the baseline your muscles are already prepared to handle, unless you are starting from a relatively detrained state.

A Practical Framework for Rucking and Muscle Goals

If your goal is muscle gain, rucking alone is not the tool for the job. But it does not deserve dismissal either. Here is how it fits into different training goals:

• Fat loss with muscle retention: Rucking burns more calories than walking and helps preserve lean mass during a deficit. Pair it with resistance training and adequate protein for the best results.
• General fitness: Two to three rucks a week at moderate load builds cardiovascular capacity, trains muscular endurance, and provides a low-barrier outdoor activity. Expect postural improvements and modest leg and core conditioning, but not visible hypertrophy.
• Strength athletes: Rucking serves as active recovery or low-impact conditioning on off days. Keep loads moderate and distances reasonable to avoid the interference effect with your lifting sessions.
• Older adults: Loaded walking can meaningfully improve muscle mass percentages and strength in people who are starting from a low baseline, making it a practical entry point for combating age-related muscle loss.

Progressive overload still applies, just in a different form than adding plates to a barbell. You can increase the pack weight by small increments, add distance, pick hillier terrain, or increase pace. Each of those variables raises the mechanical demand on your muscles. Just keep in mind that the adaptation you are building is primarily endurance and work capacity, not the kind of high-threshold motor unit recruitment that drives muscle growth. If you want both, you need both tools.