The old "10% rule" — never increase your training volume by more than 10% per week — is one of the most cited guidelines in recreational sport. It's also pretty flawed. The research it was based on is thin, and it doesn't account for the most important variable: how prepared your tissues already are.

The current evidence-based replacement is the acute:chronic workload ratio (ACWR), developed largely by Tim Gabbett's research group and adopted in BJSM consensus papers (Gabbett, Br J Sports Med, 2016).

The acute:chronic workload ratio in plain language

The model compares two things:

  • Acute load: what you did in the last 7 days.
  • Chronic load: your rolling 4-week average.

The ratio is acute divided by chronic. Gabbett's data on elite athletes suggests:

  • 0.8 to 1.3 (the "sweet spot"): low injury risk. Your recent work is in line with what you've been doing.
  • > 1.5 (the "danger zone"): meaningfully elevated injury risk. You spiked.
  • < 0.8: undertrained relative to your demand. Risk also rises if you then ramp.
“It's not how much you train. It's how much you change.”

What this looks like in real life

Say you've been averaging 25 km per week of running for 4 weeks. Your chronic load is 25. If this week you run 30 km, your ACWR is 30/25 = 1.2 — safe. If this week you run 45 km, your ACWR is 45/25 = 1.8 — into the danger zone.

The ratio matters more than the absolute number. A 45-km week is fine if your chronic load is 40. It's not fine if your chronic load is 20.

Caveats — the research isn't airtight

The ACWR has been critiqued in more recent literature (Impellizzeri et al., BJSM, 2020) for methodological issues. The principle — manage the change, not just the total — is solid. The exact thresholds may be less precise than originally suggested.

What's not in dispute: spiking your training is one of the most consistent predictors of overuse injury, across multiple sports and populations.

A practical framework for recreational athletes

You don't need a sports science lab to apply this. Here's a workable version:

  1. Track total weekly load. Miles run, minutes lifted, sessions played — whatever your sport is.
  2. Calculate your 4-week rolling average. That's your chronic load.
  3. Aim for weekly changes within +/- 30% of that average. Bigger ramps are reserved for deliberate macro-cycles with deload weeks built in.
  4. Plan deload weeks every 3–4 weeks. Reduce volume by 30–50% to consolidate adaptation and reset the chronic baseline if needed.
  5. After time off (vacation, illness, injury), don't return to your previous load immediately. Start at 70–80% and rebuild over 2–3 weeks.

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Other load variables that matter

Volume isn't everything. Intensity, frequency, and the specific type of stress all factor in:

  • New movement patterns. Adding plyometrics, change of direction, or sprinting after a long absence is a load spike even if total volume looks normal.
  • Surface and footwear changes. Switching from treadmill to road, or to a new shoe with very different drop, is a tissue-level change in stress.
  • Sleep and recovery. Same external load is more taxing if you're sleep-deprived. The acute load equation doesn't see this directly — you have to.

The strength training layer

Resistance training acts as a buffer against overuse injury, especially when it targets the same tissues being loaded in your sport. A Cochrane review of injury prevention (Lauersen et al., BJSM, 2014) found strength training reduced sports injury risk by approximately 50% — a much larger effect than stretching or proprioception work alone.

If you're a runner not lifting, or a lifter not running, the missing piece may be reducing your risk more than any load management tweak.

Bottom line

It's not how much you train. It's how much you change. Track your weekly load, hold changes within roughly +/- 30% of your 4-week average, build deload weeks into your plan, and back off the absolute thresholds — the principle matters more than the exact numbers. Add strength training as the most evidence-backed injury prevention layer you have.

References

  1. Gabbett TJ. The training-injury prevention paradox: should athletes be training smarter and harder? Br J Sports Med. 2016;50(5):273–280.
  2. Impellizzeri FM, et al. Acute:chronic workload ratio: conceptual issues and fundamental pitfalls. Br J Sports Med. 2020;54(20):1232–1233.
  3. Lauersen JB, et al. The effectiveness of exercise interventions to prevent sports injuries: a systematic review and meta-analysis of randomised controlled trials. Br J Sports Med. 2014;48(11):871–877.