Why movement is medicine
The surprising science of healthy joints — and what it means for the way you live.
By Professor Alister Hart
It sounds absurd, I know. That running — even running a marathon — could be good for your knees. That ultramarathoners, clocking hundreds of miles, often show no signs of joint damage on MRI scans. That moving more, not less, might actually protect your joints from arthritis. But that’s exactly what the science shows.
After my first marathon at age 42, I couldn’t walk upstairs without grabbing the handrail… for two weeks. As an orthopaedic surgeon, I knew joints. I looked inside them every day. But I hadn’t expected that level of pain — and I never imagined where it would lead.
That experience sparked a series of research studies using advanced MRI scanning to understand what really happens to our joints when we run. The results were surprising — and changed how I think about joint health, arthritis, and ageing.
Over the following years, I led the largest ever MRI studies of runners, examining not just knees, but hips and spines too. Again and again, the findings pointed in the same direction: movement wasn’t destroying joints. In many cases, it was helping them.
How do we explain this?
For decades, patients have received mixed messages. Some doctors still talk about “wear and tear,” as though using your joints naturally causes them to deteriorate.
Yet at the same time, medical guidelines recommend exercise as the first line of treatment for osteoarthritis. So which is it — does movement cause damage, or does it help prevent it?
The truth is more nuanced — and far more hopeful.
We now know that healthy joints are built to last a lifetime, even under daily pressure. Joints thrive on movement. Every time we walk, bend, or stretch, we deliver nutrients to cartilage and maintain the fluid pressure that keeps it soft, springy, and resilient. In contrast, immobility leads to degeneration. That’s why, after joint surgery, we encourage movement within hours — to prevent stiffness and accelerate healing.
It’s not just cartilage either. Bones heal faster when exposed to just the right level of load — not too much, not too little. We call this the “Goldilocks zone.” Getting that balance right can be the difference between a full recovery and long-term problems.
Of course, not all movement is equal. Poor technique, instability, or high-impact overload can cause harm. But the solution isn’t to stop moving — it’s to move smarter. With purpose. With variation. With understanding.
With Movement Is Medicine, I want to share what really happens to our joints when we move — and why exercise, applied wisely, is one of the most powerful tools we have to preserve joint health as we age.
We’ll explore:
Why exercise doesn’t cause arthritis — and may help prevent it.
What MRI scans can tell us about the real effects of running.
Why some people get joint pain, while others stay mobile for life.
How our bones, muscles, tendons, and cartilage respond to movement.
What the science tells us about the best types of movement for lifelong joint health.
I’m excited to tell you what I’ve learned as a doctor — and runner.
We’ll bust the myths that have held so many people back from living actively — and dive into the evidence from orthopaedics, imaging, biomechanics, and real patient stories. I’ll also share practical insights from surgery, research, and my own life as both a doctor and a runner.