A startling 80% of runners experience some kind of injury from training in any given year, and people don’t necessarily realize the myriad of complex biomechanics that go into running.
Even minor, seemingly insignificant biomechanical deficiencies can build up over time and cause issues long-term. If left unchecked, they can then snowball into larger errors or compensations — and that’s where the risk of injury begins to snowball.
There are four notoriously common form errors that we see most often in runners (of just about any caliber). And of these four errors, one that many runners tend to overlook is their degree of trunk lean.
Let’s take a deep dive into what trunk lean actually is and why it plays such a big role in efficient running.
What is Trunk Lean?
Even if you aren’t familiar with what trunk lean is, the name is fairly self-explanatory. Trunk lean refers to how far your torso (trunk) is pitching forward as you run. More specifically, forward lean is measured relative to your torso’s usual vertical position (such as when you’re standing up straight).
Ideal running mechanics call for 8-10 degrees of forward trunk lean. While that is an incredibly specific range to hit (and not a very big one), a slight change in posture can provide large impacts in terms of muscle activation, shock absorption, and overall injury risk.
As you can see in the image, 8-10 degrees is just enough to be visible to the naked eye without creating a substantial change in overall form. Even that slight change in posture can have a large impact on your running as a whole, as many runners have a tendency to run with a nearly vertical (or backward-pitched!) spine.
Insufficient trunk lean is often adopted by runners without really thinking about it — unless you’re a sprinter, there’s often little talk of leaning forward or pitching forward from the waist when discussing running form.
In fact, a common cue among running coaches is to “run tall.” While it’s well-intentioned, this cue often creates a very upright, “stacked” posture with the shoulders over the hips, rather than solely correcting the shoulder rounding, slouching, or excessive low back extension it targets.
Which is where an important distinction lies: keeping your spine neutral while you run does NOT require your entire trunk to be vertically upright. (A neutral spine simply implies that you retain the natural curvature of your spine all the way from your neck down to your pelvis without excessive extension or flexion anywhere.)
Ideally, you’ll take that neutral spine posture and hinge forward just ever so slightly. But, easier said than done — and rarely said. Otherwise it wouldn’t be a common form error! So, what happens if you do run with upright posture?
How Insufficient Trunk Lean Impacts Your Running
You may be wondering why the position of your trunk matters so much for a sport that primarily relies on the lower extremities, right?
Short answer: because of your biomechanics! (And because everything’s connected.)
As with most biomechanical movements, adjusting one area of the body leads to a chain reaction. Even if your torso isn’t the first thing you think of with running, it’s heavily involved with many primary muscle groups used throughout your gait.
In particular, research indicates a strong correlation between trunk lean and functionality of your leg joints.
Leaning forward at the hip, even if only a little bit, can improve your hip’s overall range of motion (ROM). Not only does this allow for better mobility at the joint, but having sufficient hip ROM is also an imperative facet for achieving full hip extension (which is necessary for that all-important triple extension).
Plus, decreased hip flexion leads to inactive gluteal muscles — which, as you may know, serve as the primary source of power generation. Without being able to recruit this powerful muscle group, your running is at a severe disadvantage.
But most people don’t realize these nuances, so they continue to train as is… which is where most people start experiencing problems beyond their performance.
Insufficient Trunk Lean and Injury Risk
As mentioned before, a slight forward lean helps improve your hip ROM, and the inverse logic applies here, too; with insufficient forward lean, you end up limiting that ROM. This not only impairs your running performance, but it also increases your risk of injury because it leads to compensatory biomechanics.
The thing about running is that it requires certain biomechanics, like extension in the leg as you’re pushing off into the next step. But, your body doesn’t necessarily know how to distinguish proper extension technique from improper methods — so, it’s easy for the body to rely on incorrect movements to achieve the same result.
Many runners with limited ROM at the hip wind up arching their lower back in order to achieve that necessary extension. As a result, the lumbar spine undergoes increased pressure, and the remainder of the kinetic chain is less capable of properly absorbing shock. All of this combined ultimately leads to issues with low back pain and increased risk of stress fracture.
A similar effect occurs when your glutes are inactive. Because your gluteal muscles are such a prominent source of power generation, when they aren’t functioning at peak capacity, your other body parts have to take on extra work that they weren’t built to handle.
Which brings us to one of the biggest (and most surprising) impacts of insufficient trunk lean: its correlation to excessive loading at the knee joint.
If your glutes aren’t active, your body will resort to the next “best” alternative: the quadriceps.
Because the quads are directly connected to your knee cap, when the muscles are overworked and taking on a majority of the loading forces, those same forces are transferred right to the knee joint. After prolonged periods of running with increased stress at the joint, you’re more susceptible to longer-term running injuries, like runner’s knee and patellar tendonitis.
So if it wasn’t clear before, it should be known: even the subtlest changes, down to the degree of your trunk lean, can play a major role in sound running form and injury prevention.
How to Achieve Proper Trunk Lean
Now, we know that you can technically benefit from simply leaning forward a bit more as you run, but it’s unlikely that you’ll make a consistent habit out of it if you aren’t deliberate in your technique. After all, running biomechanics are hardly based on arbitrary suggestions!
In order to hit that highly specific range of 8-10 degrees, your training has to match that same level of specificity: and that means distinct exercises and feedback.
Exercises to Improve Trunk Stability
One of the first steps to addressing trunk lean is to assess your foundation — which, in this case, accounts for your core stability and hip mobility.
If your core and low back muscles aren’t prepared to stabilize the trunk as you run, you’re much more susceptible to rounding or hunching in the spine. This is where practicing those tried-and-true core exercises like planks or deadbugs can promote better muscle recruitment to generate enough stability for the spine and torso.
As your body becomes more familiar with engaging the core, you can transition into more running-specific drills. Sled pulls and resisted gait drills are especially helpful, as they prompt you to work your core while also emulating common running mechanics (like triple extension) and recruiting similar muscle groups.
This core work will make up a bulk of the training needed to improve trunk stability, but it’s important to watch for any other compensations that may occur as a result of implementing trunk lean.
For instance, many runners find themselves struggling with triple extension, often as a result of limited hip extension. (And as we addressed earlier in this blog, limited ROM at the hip typically causes you to arch the low back to extend your leg behind you, and that’s no good.)
So in addition to core stability exercises, make sure you’re also diligently taking a few minutes to also stretch out your hip flexors! This will ensure that you avoid tight hips and maintain sufficient ROM so you don’t have to sacrifice powerful triple extension just for those few degrees of trunk lean.
Real-Time Feedback and Running Retraining
On top of practicing the right drills, you of course have to practice everything correctly, as well.
That’s where speaking to a running specialist will become invaluable — not only can they help guide you through your exercises, but they can also provide live feedback while you’re running to help cue sufficient trunk lean.
In our clinic, we particularly focus on running retraining via technology.
Using our IMU sensors and high speed cameras, we can have runners watch their form as they’re running while our specialists walk them through the live data being collected. This provides people with the opportunity to both see and feel the differences that trunk lean can make as they adjust their form in real-time.
The most obvious visual comes from the side view cameras, where you can observe that subtle shift in lean. But, our technology can do more than just show you what it looks like; with all the information combined, we can show you the specific data points that indicate how your joint angles and loading forces are impacted from improved trunk lean.
Common Errors in Trunk Lean
Increasing your trunk lean is as simple as that — just increasing how much you lean forward.
That’s basically all there is to it… though, there is a bit of nuance. (Because when isn’t there, when it comes to truly optimizing your biomechanics?)
When adjusting your trunk lean, be wary of two major issues: leaning too far forward, and rounding/hunching of the back. Let’s break those down a bit…
Leaning Too Far Forward
As for avoiding excessive trunk lean, it’s technically quite simple; just don’t lean forward that much. Which, of course, can be interpreted differently for every runner, so it’s often easier said than done.
It can be easy to overshoot that ideal range of 8-10 degrees, so using mental cues is a helpful method to keep excessive lean at bay. Imagine yourself leaning into a strong wind, or act like you’re Superman ripping his shirt open; that’s usually all it takes!
Rounding in the Spine
Rounding in the back or hunching at the shoulders are both quite common in runners.
Either issue can gradually sneak in through the duration of your run as your postural muscles start to fatigue. The more tired your muscles get, the less support they can provide your spine, meaning it’s at a higher risk of injury through bearing excess weight or loading forces.
So, your end goal is to keep your spine long and neutral, and to make sure that your chest is pointing forward rather than angled downward. (Remember that cue to “run tall” from before? This is what it’s intended to fix!)
And this brings us to our next important point…
Don’t Lean at the Ankle — Hinge at the Hip
Part of achieving that elongated spine is ensuring that your trunk lean originates from a proper hip hinge. Which, unfortunately, many runners don’t practice, and have therefore been misled about the efficacy of trunk lean.
In order to gain the forward motion that comes with running, your body has to shift a bulk of its weight from one leg (your stance leg) to the other (your leading leg) to carry you forward. And that weight shift is what prompts trunk lean in the first place, since you’re tipping your trunk forward for more momentum.
But many runners inadvertently shift their weight too far down the kinetic chain; rather than leaning forward at the hip, they lean at the ankle in the leading leg.
Doing so dramatically increases the dorsiflexion at your ankle, which consequently limits your hip and knee flexion and impedes your ability to properly absorb shock. This means that your lower leg effectively has to bear the loading and impact forces of your running, putting it at a significantly higher risk of injury over time.
This error is why many research articles actually discourage runners from practicing trunk lean in the first place… but that’s where hip hinge saves the day!
Hinging at the hip tilts your pelvis slightly backwards, helping to elongate your lumbar spine and maintain that neutral spinal alignment. (And remember: having a neutral spine doesn’t equate to having an upright posture! With proper hip hinge, you’ll notice alignment throughout the body, just positioned at a slight angle.)
Plus, achieving a solid hip hinge will contribute to better glute activation, so it has a direct impact on both preventing injury and improving your performance.
Lean Into It!
Trunk lean is an excellent example of how incredibly nuanced our running biomechanics can get. Simply standing just a few degrees too upright can have a major impact on our kinetic chain — it’s baffling to think about, really.
But, now that you are thinking about it, add it to your arsenal of running form necessities. Fine-tuning your mechanics (down to the specific degree) is an imperative aspect of addressing all the nitty gritty details that go into the big picture.