Background

Sudden changes in training load have been suggested to play a key role in the development of running-related injury (RRI). Since the injury mechanism also depends on the runner’s musculoskeletal load capacity, the running schedule undertaken prior to the sudden change may influence the amount of change a runner is able to tolerate before placing the runner at a high risk of RRI.

Objectives

To investigate the association between changes in weekly running distances and RRI, and to examine whether this association is modified by the type of running schedule followed.

Methods

A cohort of 261 healthy non-injured runners was included. Data on running activity were collected objectively on a daily basis using a Global-Positioning System watch or smartphone. RRIs were collected using e-mail-based weekly questionnaires. Primary exposure was changes in weekly running distances. Data were analyzed with time-to-event models producing cumulative risk difference (RD) as the measure of association.

Results

A total of 56 participants (21.5%) sustained an RRI during the 14-week study period Twenty-one days into the study period significantly more runners were injured when increasing their weekly running distance between 20%-60% compared with increasing ≤20% (RD_{21 days} = 22.6% (95% CI: 0.9%, 44.3%); p=0.041). No significant difference was found after 56 and 98 days. No significant effect-measure modification by running schedule was found.

Conclusion

Significantly more runners were injured 21 days into the study period when increasing their weekly running distance between 20%-60% compared with those increasing less than 20%.