Training-load management
Evidence: moderate
Quantifying internal load with session-RPE is well validated, and progressing gradually is sound advice. But the popular numerical rules for how much load is safe, the ‘10% rule’ and the acute:chronic workload ratio, are weak or actively contested. The reliable signal is to avoid single outsized sessions and to watch your own trend.
Not medical advice
This is a general knowledge base, not medical or dietary advice. If you are injured or unwell, speak to a doctor or physiotherapist who knows your situation.
Training load is the dose of stress a runner takes on, and managing it is the central balancing act of training: enough to drive adaptation, not so much that tissue is loaded faster than it can adapt and tips into injury or overtraining. For the injury picture it feeds into, see running injuries.
External versus internal load
Load comes in two forms. External load is the work done, measured objectively: distance, pace, time, elevation. Internal load is the physiological cost of that work to the individual, which depends on fitness, fatigue, heat and life stress, so the same external load lands differently on different runners and on the same runner on different days (Impellizzeri et al. 2020). Two runners doing the identical 10 km are not under the identical load. Managing load means tracking both, but internal load is what the body actually responds to.
Quantifying load
The most practical internal-load measure is session-RPE (sRPE): rate the overall perceived exertion of a session on a 0-10 scale, then multiply by its duration in minutes. A 60-minute run rated 7 scores 420 arbitrary units. This is a validated, near-free measure that tracks well with heart-rate-based methods (Foster 2001). Summed across a week it gives a weekly load; weekly running volume (mileage or time) is a cruder external proxy. The advantage of sRPE is that it captures intensity and the day’s internal cost, not just the kilometres.
Ramp rate and the ‘10% rule’
The instinct to cap how fast load grows is sound; the specific numbers are not. The ‘10% rule’, which limits weekly mileage growth to 10%, is lore rather than a tested threshold. A prospective study of 874 novice runners found a cautious 10% weekly progression did not reliably protect them, though jumps above 30% in a week did raise distance-related injuries (Nielsen et al. 2014). Progress gradually, yes; treat 10% as a habit rather than a safety line.
The acute:chronic workload ratio: contested
The acute:chronic workload ratio (ACWR) divides recent load (typically the last week) by accumulated load (typically the last four weeks), with a ‘sweet spot’ band said to minimise injury. It spread quickly through sport, but it is genuinely contested rather than established.
ACWR is methodologically contested
A detailed critique showed the ratio is mathematically coupled, so acute and chronic load are not independent, producing spurious correlations; that carving a continuous ratio into arbitrary risk bands has no basis; and that using it to prescribe load assumes a causal effect no study has established. The authors concluded there is no sound evidence for ACWR in load management or injury prevention, and that the widely reproduced ‘sweet spot’ figure is flawed (Impellizzeri et al. 2020). Treat any app or coach selling an ACWR ‘danger zone’ with scepticism.
One outsized session beats the weekly total
The clearest empirical signal points away from weekly ratios and towards single sessions. In a cohort of 5,205 runners across 588,071 sessions, a run more than 10% longer than the longest run of the previous 30 days raised the overuse-injury rate, climbing with the size of the spike to a hazard rate ratio of 2.28 for a session more than double the recent long run (Johansen et al. 2025). In the same data, week-to-week mileage change and the ACWR showed no positive association with injury, and large ACWR spikes were if anything protective (Johansen et al. 2025). The actionable lesson: do not let one run run away from your recent training.
Connecting load to monitoring
Quantifying load is only half the job; the other half is checking how it is being absorbed. Brief daily subjective wellness checks are more sensitive to load than most gadgets, sRPE tracks the load itself, and HRV is read as a 7-day trend rather than a daily number. The detail lives on the training monitoring page. Load figures mean little without watching the body’s response, because the same load injures one runner and not another.
Practical synthesis
What load management actually means
Progress gradually rather than to a magic percentage. Never let one run be wildly longer than your recent long runs, the single best-supported rule here. Track internal load with sRPE and your response with a daily wellness check. Individualise: build from your own base (see base building), balance volume against intensity, and watch your own trend, not someone’s ratio. After injury or a long break, rebuild deliberately (see return to running).
For where load management sits in the wider picture of how training works, see the basics.