Why Your Running Back Pain Might Actually Be a Leg Problem
Every time Amy built up her training, the same thing happened. Her lower back would start to tighten and grumble, always around the same point in her mileage. It settled with rest and hands-on treatment, then crept back the moment she pushed on again. If you run, you probably know that feeling: a niggle that keeps returning, always just as you are getting into your stride.
Here is what we have learned after testing a lot of runners. The spot that hurts is very often not the spot that needs the work. And the reason a problem keeps coming back is usually hiding somewhere you would never think to look, and somewhere you simply cannot feel.
The runner whose stronger leg was the problem
Amy is one of our regular runners. She comes in monthly for maintenance physio, which keeps on top of the tight areas and keeps her running well. That treatment had been keeping her recurring back tightness at bay for a long time. What we wanted to understand was why it kept coming back in the first place.
So we tested her. And the results were not what anyone expected.
On a standard strength check, the leg on her painful side was actually her stronger leg. On paper, nothing was wrong. But when we measured how fast that leg could produce force, the number was around 85% lower than the other side. Her strong leg was slow. And in running, slow is a problem.
“You cannot feel a difference like this. Amy’s running looked completely normal. It only showed up when we measured it.”
Why speed of strength matters more than strength
When you run, each landing lasts a fraction of a second. In that tiny window your leg has to switch on, absorb your full body weight coming down, and spring you back up. It is not enough to be strong. You have to be strong quickly.
If one leg produces its force too slowly, it cannot cushion the landing properly. That extra load has to go somewhere, so it travels up the chain into the hip, the pelvis and the lower back. You feel it in your back. But the cause is sitting lower down, in a leg that looks perfectly fine.
This is the hidden pattern we keep finding in runners. A recurring problem in one place, driven by how a leg is loading and how fast it produces force somewhere else entirely. It is invisible to the eye and invisible to a basic strength test. The only way to find it is to measure it.
How we found the real cause
At our clinic in Carlyon Bay, St Austell, we use two tools that work together to see what the eye cannot. The Run Lab® is our 3D gait analysis. It shows us exactly how you move when you run, so we can improve your efficiency and reduce your injury risk. VALD® performance testing is different. It precisely measures how much force different areas of the body produce, how effectively, and most importantly how fast, using a series of movement screens across different pieces of equipment.
Together they build a complete picture of how an athlete moves and performs. In Amy’s case, the testing did not replace the hands-on physio that had kept her going. It finally showed us the why behind the recurring problem, so we could build a plan to strengthen that slow leg, restore the symmetry between her sides, and address the cause at its source rather than chasing the symptoms up in her back.
It also means we can tell, objectively, when she is ready to push her training on again. No guessing.
Frequently asked questions
Running-related back pain that flares with mileage is often a load problem rather than a back problem. If one leg is not absorbing the shock of each landing efficiently, that load travels up into the pelvis and lower back. The back is where you feel it, but the cause can sit lower down the chain. Objective testing helps find where the load is actually coming from.
Rate of force development is how quickly a muscle switches its strength on. It is different from how strong you are. You can be strong but slow. In running it matters because you only have a fraction of a second to absorb the shock of each stride, so a leg that produces force slowly cannot cushion the landing well.
Yes. In Amy’s case, her painful leg was actually her stronger leg on a basic strength measure. The problem only showed up when we measured how fast she produced force, which was around 85% lower on that side. Measuring how quickly a muscle works, not just how strong it is, can reveal what a standard strength check misses.
Both are included in our advanced treatment pathways and either can be used as an initial assessment session. The Run Lab® analyses how you move when you run, so we can improve your movement efficiency and reduce your injury risk. VALD® performance testing precisely measures how each leg produces force, and how fast, using a series of movement screens across different pieces of equipment. Together they build a complete picture of how a runner moves and performs.
No. Runners come to us both to sort out a recurring problem and to understand their movement and build resilience before injury strikes. Many of our regular runners, like Amy, come for monthly maintenance physio to stay ahead of problems and then use The Run Lab® and VALD testing sessions throughout the season to guide their training and rehab.
We are in Carlyon Bay, St Austell, in mid-Cornwall, and we see runners and active people from across the county, including Truro, Newquay, Fowey, Falmouth, Bodmin and St Austell itself.
About the author
Lou Nicholettos is a clinical specialist Physiotherapist with two Master’s degrees. She is the founder of Cornwall Physio, the multi-award-winning specialist physiotherapy clinic in St Austell. Cornwall Physio was awarded Physiotherapy Clinic of the Year, South of England, 2025 to 2026.
Come and talk to us
If you would like to find out whether Cornwall Physio is the right fit for you, you can book a free discovery call or enquire about cost and availability directly via our website or by calling the clinic on 01726 815 189.
Speak soon, Lou
