Running injuries mostly come from doing too much too soon. The safest plans build gradually from what you're actually doing now, not from what you'd like to be doing.
Weekly distance increases
- The 10% rule: "increase weekly distance by no more than 10%" is a coaching convention more than a proven threshold. In a randomised trial of novice runners, Buist et al. (2008) found a graded programme built on the 10% rule did not reduce injuries compared with a faster standard programme.
- Larger jumps: these do carry risk. In a cohort of novice runners, Nielsen et al. (2014) found that increasing weekly distance by more than 30% over two weeks was associated with more overuse injuries, particularly some injury types.
- Takeaway: keep increases modest. Stay well under 30%, and use about 10% as a sensible default. For runners on very low distance, 10% is a tiny absolute amount. Adding a kilometre or two is reasonable even when that is more than 10%.
Load ratio
Gabbett (2016) popularised comparing the last week's load with the average of the previous four (the "acute:chronic workload ratio"). Trainer's dashboard shows it as your load ratio: the last 7 days' distance divided by your 4-week weekly average. Ratios of about 0.8–1.3 were associated with lower injury risk and spikes above about 1.5 with higher risk. The method has been criticised on statistical grounds (Impellizzeri et al., 2020). Treat it as a rough warning sign, not a precise threshold. The dashboard warns you when your load ratio is above 1.5.
Recovery weeks
Most established programmes (for example Pfitzinger's) build for 2–3 weeks and then reduce distance for a week. This is a coaching convention rather than a tested rule. The reduction lets adaptation catch up and lowers accumulated fatigue. Recovery weeks keep some quality but at reduced volume.
Long runs
The long run is the cornerstone of endurance, but it should grow gradually. Daniels limits it to about 25–30% of weekly distance. That works for shorter races, but two cases need more room:
- Few run days: runners who only run 3 days a week can't keep it that low without making the other runs trivially short.
- Half marathon and marathon: long runs that get close to race distance build endurance and confidence, and are a chance to practise fuelling. Half marathon plans commonly build to 16–19 km, and marathon plans to 26–32 km. At 30% of the week, a 30 km long run would need a 100 km week, far beyond most recreational runners. So for these goals, the long run can be a bigger share of a smaller week.
The cost is that more of the week's running is concentrated in one day, so the rest of the plan has to keep the long run's growth gradual.
Returning from a break or starting out
If you've had a recent break of two weeks or more, or have under 8 weeks of running history, the dashboard flags it, and your plan should start below your previous peak. They should add frequency before distance, and add distance before intensity.
How Trainer applies it
- Weekly increase: a week may exceed the highest week so far (or, for week 1, your current 4-week average) by at most 10%, or 2 km if that is larger.
- Recovery week: after at most 3 build weeks comes a recovery week, at least 10% lower than the week before. This applies to plans of 6 weeks or more.
- Long run cap: the longest run of a week is at most 30% of the week's distance with 5+ run days, 35% with 4, and 40% with 3 or fewer. For half marathon goals it's at least 40%, and for marathon goals at least 50%. It isn't checked in race weeks.
- Session length: sessions respect your maximum session length, if you set one.
Sources
- Buist I, et al. No effect of a graded training program on the number of running-related injuries: a randomized controlled trial. Am J Sports Med. 2008;36(1):33–39.
- Nielsen RØ, et al. Excessive progression in weekly running distance and risk of running-related injuries: an association which varies according to type of injury. J Orthop Sports Phys Ther. 2014;44(10):739–747.
- Gabbett TJ. The training–injury prevention paradox: should athletes be training smarter and harder? Br J Sports Med. 2016;50(5):273–280.
- Impellizzeri FM, et al. Acute:chronic workload ratio: conceptual issues and fundamental pitfalls. Int J Sports Physiol Perform. 2020;15(6):907–913.
- Pfitzinger P, Douglas S. Advanced Marathoning. 2nd ed. Human Kinetics; 2009.
- Daniels J. Daniels' Running Formula. 3rd ed. Human Kinetics; 2014.