Table 3.
Cumulative risk differences (cRD) for running‐related injury*.
| Running distance the first week | cRDs [95%CI] for > 3 to ≤ 6 km within strata of BMI | cRDs [95%CI] for > 6 km within strata of BMI | |||||||
|---|---|---|---|---|---|---|---|---|---|
| ≤ 3km | > 3 to ≤ 6 km | > 6 km | |||||||
| Injury/ no injury | cRD [95%CI] | Injury/ no injury | cRD [95%CI] | Injury/ no injury | cRD [95%CI] | ||||
| After 10km: | Low BMI [≤30] | 4/196 | Reference | 7/173 | 1.0% [−3.4%; 5.3%] p=0.67 | 4/224 | −1.6% [−5.8%; 2.5%] p=0.44 | 1.0% [−3.4%; 5.3%] p=0.67 | −1.6% [−5.8%; 2.5%] p=0.44 |
| High BMI [>30] | 4/54 | 5.8% [−0.5%; 12.2%] p=0.07 | 4/38 | 7.3% [0.2%; 14.3%] p=0.04 | 5/33 | 12.7% [5.2%; 20.2%] p<0.01 | 1.5% [−7.0%; 9.9%] p=0.74 | 6.9% [−2.0%; 15.8%] p=0.13 | |
| After 20km: | Low BMI [≤30] | 5/195 | Reference | 13/167 | 2.5% [−4.3%; 9.4%] p=0.47 | 13/215 | −1.0% [−7.4%; 5.5%] p=0.78 | 2.5% [−4.3%; 9.4%] p=0.47 | −1.0% [−7.4%; 5.5%] p=0.78 |
| High BMI [>30] | 4/54 | 5.4% [−4.5%; 15.4%] p=0.28 | 7/38 | 14.3% [3.3%; 25.3%] p=0.01 | 7/31 | 16.2% [4.4%; 28.0%] p<0.01 | 8.8% [−4.4%; 22.1] p=0.19 | 10.8% [−3.1%; 24.7%] p=0.13 | |
CI = confidence interval. Km = kilometer. BMI = body mass index
Chi2 tests for difference between all six groups were performed after 10 km and 20 km revealing a significant difference across all six groups (p<0.01).
Two analyses are presented: after 10 km and after 20 km. The reference risks for the runners with a BMI ≤ 30 and running less than 3 km during the first week were 3.1% [0.1% to 6.1%] after 10 km and 6.5% [1.7% to 11.2%] after 20 km. Kilometers at risk for the 749 novice runners were 14,676 km. Measure of effect modification on additive scale (Absolute Excess Risk): 11.7% [−3.6% to 27.0%], p=0.13 (BMI>30 and >6km after 20 km) and 6.3% [−8.6% to 21.2%], p=0.41 (BMI>30 and >3 to ≤ 6 km after 20 km).