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.

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