If uphill running feels fine but downhill running brings on knee pain, you're not imagining it, downhill running places genuinely different demands on your knee than running on the flat or uphill. Here's why it happens and what to do about it.
Downhill Running Is a Different Load Entirely
Running downhill isn't just "less effort" than running uphill, in many ways, it's harder on your body. Each time your foot lands, your leg muscles are working eccentrically, lengthening under load to control your speed and absorb impact. That braking action, repeated hundreds of times over a descent, puts significantly more stress through the knee than flat or uphill running.
This is why downhill running is one of the most common triggers for knee pain, even in runners who have no issues on flat terrain.
The Usual Suspect: Patellofemoral Pain
The most common cause of downhill knee pain is patellofemoral pain syndrome, pain around or behind the kneecap. Downhill running increases the load on the patellofemoral joint specifically, because of the angle your knee is bent at on impact and the extra braking force needed to control your descent.
Typical signs:
Dull ache around or behind the kneecap
Pain that's noticeably worse on descents than flat or uphill sections
Similar discomfort with stairs (especially going down) or prolonged sitting
Pain that builds gradually over a run rather than appearing instantly
Other Possible Causes
While patellofemoral pain is the most common explanation, a few other things can also show up specifically on downhill sections:
IT band syndrome — pain on the outside of the knee, often worse with the repetitive knee bending downhill running requires
Quad fatigue or weakness — if your quads can't adequately control the eccentric load, more force transfers through the knee joint itself
Poor downhill running mechanics — overstriding or leaning back on descents increases braking forces and knee load
Why It Happens: Load, Not Just "Bad Knees"
Downhill knee pain is rarely about anything being structurally wrong with the knee. It's almost always a load-tolerance issue, your quads and the tissue around your kneecap aren't yet conditioned to handle the eccentric demands of descending. This is especially common when:
You've recently added more downhill running or trail races to your training
Your training has been mostly flat, and you're preparing for a hilly race
Your quad strength hasn't kept pace with your running volume
You're increasing distance or vertical gain quickly without a gradual build
What Helps
Build eccentric quad strength
Since downhill running is fundamentally an eccentric load, targeted eccentric strength work, like slow, controlled squats or step-downs, helps your knee tolerate that demand.
Introduce downhill running gradually
If you're preparing for a hilly or trail race, practice descents in training rather than encountering significant downhill load for the first time on race day. Start with shorter, gentler descents and build up.
Check your downhill mechanics
Shorter, quicker strides on descents generally reduce impact forces compared to overstriding, which increases braking load through the knee with every footfall.
Don't just stretch and hope
Downhill knee pain is a load and strength issue, not usually a flexibility issue. Time spent on quad and hip strength will generally do more than stretching alone.
When to Get It Checked
If the pain persists beyond a couple of sessions, changes how you run, or doesn't ease with a few days of easier training, it's worth getting assessed. A physio can confirm exactly which structure is involved, how much load your knee can currently tolerate, and build a strength and training plan that gets you handling descents confidently again, rather than dreading every downhill on race day.
The Bottom Line
Knee pain on downhills usually comes down to load your knee isn't yet prepared for, not a structural problem. With the right strength work and a gradual build in downhill exposure, most runners can train through hilly terrain pain-free.
Kye Simpson, Senior Physiotherapist at Streamline Physiotherapy, Thirroul.