Does training volume pay off?

The committee of the Corniche Striders, a fictional community running club, wants to launch a membership drive around a training programme. A draft poster reads: “Every extra 10 km a week takes 3.6 minutes off your 10K — our race data prove it.”

The club secretary is uneasy and asks you to check the claim before the poster goes to print, using the results of the club's last 10 km race (running_club, synthetic): age, sex, self-reported average training distance over the previous eight weeks, and chip finish time for 500 finishers.

Decisions that depend on your answer:

• whether the poster's wording is defensible, and what it should say instead;
• whether the club should advise beginners to ramp up mileage quickly (injury risk is a real cost);
• what data the club would need to measure the programme's effect properly.

The club, race and runners are synthetic, generated for teaching.