Spine Shear Load During Loaded Carries

Let’s be honest—loaded carries look simple. Pick up something heavy, walk a few steps, put it down, done. But under that rugged simplicity hides a biomechanical balancing act, and your spine? It’s smack in the middle of the tension. Whether you're a firefighter lugging a 60-pound pack or a fitness enthusiast hauling kettlebells during a farmer's walk, one thing's clear: your spine doesn't just bear weight. It negotiates force, redirects pressure, and absorbs shock—all while you move.

 

Now, here’s the thing most people forget: not all stress is created equal. Sure, compressive load gets a lot of attention. Everyone worries about vertical pressure squashing their discs like pancakes. But spinal shear force? That one's sneakier. Shear stress occurs when one vertebra tries to slide forward or sideways against another. Imagine a Jenga tower, where one block shifts out of alignment. That sliding motion—not the stacking—is what shear stress looks like. And in loaded carries, particularly asymmetrical ones like suitcase carries, shear load is very much in play.

 

Before we dive into solutions, let's get a grip on definitions. A loaded carry is any walking movement performed while carrying a weighted object. Farmer’s carry (equal weight in each hand), suitcase carry (weight in one hand), yoke walk (heavy barbell across the back), bear hug or sandbag carry—they all count. These movements have become staples in strength training because they build grip strength, core stability, and total-body endurance. But with poor form or programming, they can load the spine in ways that accelerate wear and tear.

 

So who should care? This piece is for anyone who lifts, walks, or works with loads. That includes strength athletes, tactical professionals, rehab patients, and even desk workers using carries as part of their corrective exercise plan. If your goal is spinal longevity, understanding how to reduce shear force during loaded carries is essential.

 

Let’s clear up a big myth first: "brace your core" isn't a magic spell. It gets tossed around like salt on fries, but very few people understand what proper bracing actually feels like. True bracing requires creating intra-abdominal pressure—kind of like filling a balloon in your belly to stabilize your lumbar spine. Not sucking in. Not squeezing abs like you're prepping for a photo shoot. According to McGill et al. (2010), proper bracing can significantly reduce anterior shear forces by up to 25% during loaded movements, assuming neutral alignment is maintained.

 

Speaking of alignment, posture is everything. No, we’re not talking rigid military posture or "sit up straight!" orders from childhood. Spinal neutrality refers to maintaining the natural S-curve of your spine. In loaded carries, this means preventing the pelvis from dumping forward (anterior pelvic tilt) or letting the ribs flare upward. Both throw your center of mass off and increase anterior shear in the lumbar region.

 

Then comes gait. We’re bipeds—walking is our default setting. But throw in an uneven load, and the body starts to compensate in subtle but spine-wrecking ways. A suitcase carry often causes lateral lean or asymmetric hip drop if the core and glutes aren’t fully engaged. Over time, these minor tweaks in movement pattern can create chronic stress on the L4-L5 and L5-S1 vertebrae, which are already the most shear-prone segments of the spine.

 

Let’s pull in some numbers. A study from the University of Waterloo (Canada) used motion capture and force plates to measure spinal shear during various loaded carries. In a sample of 20 trained males, anterior lumbar shear forces during a 30-kg unilateral carry increased by 31% compared to a bilateral carry of the same weight. The asymmetry forced a subtle but measurable spinal rotation and lateral flexion that shifted the force angle from pure compression to combined shear. That combo? It’s not great for long-term spinal health.

 

But here’s the twist—not everyone’s in love with carries. Some physical therapists caution against their overuse, especially in populations with existing spinal pathology like disc herniations or spondylolisthesis. Dr. Stuart McGill himself advises modifying or avoiding loaded carries in patients with certain spinal instabilities. And he’s the guy who made carries cool again.

 

Beyond the science, there's the human element: fear. If you've ever tweaked your back during a workout, you know the dread that follows. It lingers. And when someone hands you a heavy kettlebell and tells you to "just walk," you might hesitate. That emotional hesitation isn't just psychological—it changes how your body moves. Guarding patterns, shallow breathing, and asymmetric step lengths all increase spinal load unpredictably.

 

Now, let’s zoom out and talk real-world context. Firefighters carry people. Soldiers ruck through deserts. Movers hoist awkward couches up stairs. These professionals don’t get to say, "My back feels off today." What do they do differently? Most use structured training programs to build carry capacity progressively. Tactical athletes often employ weighted vest training before moving on to heavy unilateral carries. They also use external support systems, like lumbar harnesses, to mitigate direct spinal load when possible.

 

For the average gym-goer, the path is simpler. First, choose your implement wisely. Suitcase carries? Start light and short. Farmer's carries? Match your loads precisely. Sandbags? Keep them tight to your chest to minimize torque. Second, dial in your bracing. Use a balloon analogy: inhale 360 degrees into the belly, then hold tension without letting the ribcage flare or spine arch. Third, walk like you're balancing a book on your head. Chin neutral, ribs stacked over pelvis, no wobble.

 

Want a simple test? Carry a moderate kettlebell in one hand, walk 10 meters, then switch hands and walk back. Record yourself. Is your torso leaning? Are your hips wobbling? Is your step cadence uneven? If yes, regress the load or switch to bilateral carries until symmetry improves. Progress gradually, like you would with squats or deadlifts. Loaded carries deserve the same respect.

 

Celebrities have learned this lesson the hard way. Several CrossFit athletes, including former Games contenders, have publicly shared how overdoing carries led to spinal compression injuries or disc issues. NFL linemen, too, are routinely flagged for spinal degeneration linked to years of unbalanced, heavy carries during off-season farm work and in-practice drills. Their lesson? Build capacity, not ego.

 

So where does this leave us? The spine is a load distributor, not a shock absorber. It needs teamwork from the glutes, core, diaphragm, and even the lats. The key to safe loaded carries isn’t just strength. It’s control. Awareness. And progressive overload—not just in weight, but in how well you manage form under fatigue.

 

Let’s wrap with clarity. Loaded carries can strengthen the body like few other exercises, but they also come with risk. Shear force on the spine is invisible but dangerous, especially when alignment, breathing, and load management are ignored. If you're going to walk with weight, make every step count. Load wisely, brace intentionally, walk deliberately.

 

Disclaimer: This article is for informational purposes only and does not constitute medical or fitness advice. Always consult a qualified healthcare provider or certified professional before starting any new exercise program, especially if you have preexisting health conditions.

 

So next time someone tells you to "just carry that," pause. Check your form, check your breath, and check your ego. Because your spine? It remembers everything.