How do I safely increase running mileage?
Increase weekly mileage by no more than 10% per week, then take a down week every 3-4 weeks where you reduce volume by 20-30%. Add one run or lengthen existing runs, not both. Monitor aches and sleep; if either worsens, hold mileage steady for 2 weeks before increasing.
The 10% rule is a good starting guideline, but the real answer is: increase mileage in a pattern of 3 weeks up, 1 week down. Week 1: 30 km. Week 2: 33 km. Week 3: 36 km. Week 4: 27 km (down week). Week 5: resume at 36-40 km. This rhythm respects two biological realities — your aerobic system adapts faster than connective tissue, and your tendons need planned recovery windows to consolidate gains. Adding mileage without down weeks is the #1 cause of stress fractures and Achilles problems in intermediate runners. Two other rules: add volume by extending existing runs before adding new run days, and never increase mileage AND intensity in the same week. If you're adding a speed session, hold volume flat. If you're adding a long run, hold intensity flat. Monitor these warning signs: resting heart rate up 5+ bpm, sleep quality dropping, morning stiffness lasting beyond warm-up, or any localized pain that persists more than 48 hours. Any one of these means hold mileage steady for 10-14 days before pushing again. The goal is consistent upward progression over months, not rapid jumps that end in injury.