Too Much Too Soon: Training Load and Injury

If you look at the circumstances around most running injuries, a common pattern emerges: the person recently increased their mileage, started a new program, returned from a break, or changed their training surface. Training load errors are the leading cause of overuse injury, and understanding how to manage them is the most practical thing a runner can do.

The 10% rule and its limitations

The 10% rule - don't increase weekly mileage by more than 10% - is a useful starting point but oversimplifies a complex relationship. It doesn't account for intensity, which matters as much as volume. Adding a hard tempo run to a week where total mileage stays the same is still a significant load increase.

Acute:chronic workload ratio

A more useful framework is the acute:chronic workload ratio (ACWR), developed in team sport research but applicable to running. The concept is simple: your current week's load (acute) compared to your average load over the previous four weeks (chronic). A ratio between 0.8 and 1.3 represents a 'sweet spot' for adaptation without elevated injury risk. Ratios above 1.5 are associated with sharply higher injury incidence.

Tracking your own ACWR: a worked example

This doesn't require an app - a notebook or spreadsheet works fine. Record your total weekly distance (or time, for mixed training), then calculate your 4-week rolling average as you go.

• Week 1: 20km, Week 2: 22km, Week 3: 24km, Week 4: 26km → chronic average = 23km
• Week 5 acute load 26km ÷ chronic 23km = ACWR 1.13 - inside the 0.8-1.3 sweet spot
• Week 5 acute load jumps to 34km ÷ chronic 23km = ACWR 1.48 - approaching the danger zone above 1.5

We see this exact pattern often with clients training on the Bondi to Bronte coastal path: a runner comfortable at 20-25km a week decides to add the full clifftop loop plus the stairs at Tamarama on top of their existing sessions, jumping straight to 35km in a single week because the weather's good and the path is right there. The stairs and undulating terrain also add a load spike beyond what the distance alone suggests, since eccentric loading on the calves and Achilles is higher on descents than flat running. That combination - a distance jump plus a terrain change in the same week - is a classic setup for Achilles or calf strain.

Red weeks and green weeks

A practical way to implement this: after every two to three weeks of progressive loading, schedule a recovery week where total volume drops by 20-30%. This resets the nervous system, consolidates adaptation, and prevents the cumulative load from becoming an injury-level stimulus.

Other load variables that matter

• New shoes: can change load distribution enough to cause injury in the first 2-3 weeks
• Trail to road or vice versa: surface change alters impact mechanics
• Returning from illness: fitness recovers faster than tissue capacity after a break
• Race tapers followed by return to training: tissues are sensitised after a race

FAQs

Is ACWR still useful if I don't run every week?

Yes, but treat your chronic average cautiously if your training has been inconsistent - a low 4-week average from an interrupted month will make even a modest return-to-running week look like a small ACWR jump when your tissue capacity has actually dropped further than the number suggests.

Does cross-training count towards training load?

For injury risk specific to running, what matters most is running-specific load - the impact and eccentric demand cycling or swimming don't replicate. Track running volume separately rather than lumping all training into one number.