Running Injury

Musculoskeletal injury in recreational runners, dominated by overuse injuries — damage from training that is tolerable in any single part but cumulatively exceeds the body's capacity to recover. "Runner's knee" (patellofemoral pain) was among the most common complaints in a 2021 Orthopaedic Journal of Sports Medicine study of 3,669 runners.

The load question

Folk guidance says increase weekly mileage by no more than 10%. The largest wearable cohort to date tested that unit of analysis and found it is the wrong one.

Garmin-RUNSAFE Running Health Study (Schuster Brandt Frandsen et al., BJSM 2025): 5,205 recreational runners in 87 countries, 18 months, 588,071 GPS-tracked sessions; 35% reported an injury, mostly overuse.

Risk was keyed to a single session's distance relative to the longest run in the previous 30 days:

Spike over longest recent run	Hazard rate ratio
≤ 10% (reference)	1.00
> 10–30%	1.64
> 30–100%	1.52
> 100%	2.28 (95% CI 1.50–3.48)

Week-to-week distance change: no association. Acute:chronic workload ratio: no positive association either. The authors' conclusion is that the safe increase in a single long run "may be vastly less than 10%".

Limits of the evidence

• Injury self-reported; intensity and biomechanics not measured; one cohort, exploratory, industry-sponsored (Garmin).
• Authors ask for replication before the session-spike rule becomes prescriptive.
• Nothing paged yet on footwear, surface, cadence or strength work as modifiers.

Related

• Can Joggers Outrun Injury (Economist) — anchor source (lede-only capture; study read via its summaries).
• Minimum Effective Dose of Exercise — the lower end of the dose curve; this page is the upper end.
• Step Count Targets — same wearable-cohort method, walking.