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Running7 min read · Dr. Nevin Saju, PT, DPT
The short answer
You get injured when you increase mileage because your heart, lungs, and motivation adapt faster than your tendons and bones. Your fitness says go while your tissues are still catching up. The fix isn't running less forever. It's building capacity with strength work, smarter progression, and honest symptom tracking.
About half the people on my discovery calls are runners, and a lot of them describe the exact same calendar.
The block starts great. Week four or five feels strong. Then the long run creeps up and something flares. Shins, Achilles, a knee, a hip. One runner summed it up: “It comes back every half marathon season.” Another: “Shin splints every time I up my mileage.”
These aren't lazy people. They follow the plan. Some of them stretch their calves 20 minutes a day and still feel tight. And most of them don't just want to finish. They want to run faster.
If that sounds like your pattern, it isn't bad luck. It's predictable, which means it's fixable.
Why do I get injured every time I increase my mileage?
Because the parts of you that feel ready adapt faster than the parts that take the beating. Your heart, lungs, and motivation improve quickly. Your tendons and bones take much longer to catch up.
Muscle and your cardiovascular system have a rich blood supply and adapt relatively fast. Tendons and bone don't. Research on tendon tissue shows the structural remodeling that makes a tendon stronger takes weeks to months. So you can feel fitter than ever while your Achilles is still working at last month's capacity. Picture a bigger engine bolted onto the same chassis.
That's what an overuse injury is. Not one bad step. Thousands of moderate loads repeated until the total demand outpaces what the tissue can handle. Your Achilles alone takes loads of 6 to 12 times your body weight while you run. Add a few weeks of extra miles and the math stops working.
Research on running injuries backs this up. Training errors, mostly rapid jumps in volume, intensity, or duration, are linked to 60% to 80% of Achilles tendinopathy cases. Studies report that up to 80% of runners get injured in a given year, and a previous injury in the last year is the single strongest predictor of the next one.
That last part is why the cycle repeats. When the pain goes away, it feels like you're healed. But in research on runners with Achilles tendinopathy, only 1 in 4 who were fully pain free had actually restored full muscle and tendon function. You go back to full mileage on tissue that's still underprepared, and you end up right back where you started. If you've done PT that cleared the pain but never broke the pattern, I wrote about what to do when physical therapy didn’t work.
The spot that hurts also isn't always the spot that's failing. Pain tends to show up where your body is overworking to compensate. Weak hips shift extra load down the chain, which is why knee pain in runners often isn't really a knee problem. In one study, runners with shin splints showed a 56% deficit in calf endurance compared to healthy runners. Shin, Achilles, and foot pain and hip or groin pain are often the messenger, not the source.
Then there's everything outside of running. Research links short sleep to higher injury risk, including stress fractures, and life stress adds to the total load your body is managing. A brutal work month counts, even if your training log doesn't show it.
Your body isn't broken. It just can't handle what you're asking of it yet.
Your fitness is ready for the next block. Your tendons haven't caught up yet.
Is the 10% rule real, and how much should I increase my mileage?
Not as a universal rule. Research doesn't support a fixed 10% weekly cap that works for everyone. A safe increase depends on your history, your current capacity, and how your body responds, which is why two runners on the same plan can have completely different blocks.
The most solid 10% finding in the research actually isn't about mileage. It's about cadence. In one study, increasing step rate by 10% reduced load on the kneecap joint by 14%, and a 5% bump reduced energy absorption at the knee by up to 20%. One caveat: cadence only means something relative to your pace, so treat it as a tool, not a number to chase.
What the research does support:
- Progress by tolerance, not the calendar. Volume goes up when your body says yes.
- Recover between big days. Long runs and speed sessions need 2 to 3 days of lower load before you repeat that kind of stress.
- Check the next morning. Morning stiffness and pain tell you more than how the run felt.
- Avoid spikes. Injury risk rises when short term load jumps well above what you've built over the previous 3 to 4 weeks. One long run far beyond anything recent counts.
- Change one thing at a time. New shoes, new surfaces, more hills, more speed. Each one shifts load, and stacking them in the same week is how blocks fall apart.
So how much should you add each week? Less than your motivation wants, and as much as your next morning allows.
Keep breaking down at the same point every block?
What actually helps you build mileage without getting hurt?
Build the chassis, not just the engine, and let your symptoms steer the plan.
1
Strength train the parts that take the beating.
Calf and hip weakness are documented risk factors, and progressive strength work makes tendons thicker, stronger, and stiffer. Stretching 20 minutes a day might feel good, but it won't build that capacity. My baseline for runners is 30 single leg calf raises per side, and the first few weeks of strength gains are mostly your nervous system learning, so give it time.
2
Use the traffic light rule.
Green: symptoms settle within a day or two, so keep going. Yellow: they hang around 3 to 4 days, so scale your volume down without stopping completely. Red: sharp or escalating pain means drop back to your last comfortable level and get it looked at.
3
Space out your hard days.
Give long runs and speed work 2 to 3 easier days before repeating them. Your tendons recover on a slower clock than your lungs.
4
Count sleep and stress as training load.
On short sleep or a heavy life week, hold your mileage steady instead of pushing it. The plan should flex with your life.
5
Get assessed above and below where it hurts.
Testing calf endurance, hip strength, and single leg control shows what's actually limiting you. That's how we approach physical therapy for runners, and you can read what other runners have said about breaking the cycle.
When to see a doctor first
Get checked by a physician before continuing to run if you have:
- Pinpoint tenderness directly on a bone, like your shin, midfoot, or deep in the front of your hip
- Pain at rest, or pain that wakes you up at night
- Severe pain hopping on that leg, or trouble bearing weight
- Pain that keeps getting worse even after you've stopped running
- Rapid, visible swelling in a joint like the knee
- Swelling, redness, or tenderness in one calf
- Sudden weakness, like being unable to do a single calf raise or your foot dragging
- Numbness, tingling, or pain shooting down your leg
- Numbness in the groin or saddle area, or changes in bladder or bowel control
- Fever, unexplained weight loss, or pain after a major fall or accident
Common questions
Should I stop running when something hurts?
Usually not completely. If symptoms settle within a day or two, keep going. If they linger 3 to 4 days, scale volume down rather than shutting everything off, and get sharp or worsening pain checked.
Do runners need strength training?
Yes. Calf and hip weakness are documented risk factors for running injuries, and progressive strength work builds tendons that handle load better. It's how you get faster without breaking down, not just how you avoid injury.
Why does my pain move from my shins to my knee to my hip?
When one area can't handle its share, your body shifts the work somewhere else. Pain shows up where you're overworking, which is usually not where the problem started. Chasing each new spot without finding the source keeps the cycle going.
How do I know if it's a stress fracture?
Warning signs include pinpoint tenderness on the bone, pain at rest or at night, and severe pain when you try to hop on that leg. If any of those sound familiar, see a physician before you keep running.
Keep reading
Revenant Physical Therapy
Want to finish a block in one piece?
Book a free 15 minute discovery call. Tell me where your last few blocks broke down, and we'll figure out whether Revenant is the right fit to change that. Revenant Physical Therapy is based in Farmers Branch and works with runners from Addison, Carrollton, and across North Dallas.
Written by
Dr. Nevin Saju, PT, DPT
Founder of Revenant Physical Therapy in Farmers Branch. Three open-heart surgeries taught him what it takes to trust your body again. Now he helps runners, lifters and active adults do the same. More about Nevin →
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