STUDY DESIGN: A prospective cohort study with a study period of 14-weeks.
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% (RD21 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%.
LEVEL OF EVIDENCE: Prognosis, level 1b. J Orthop Sports Phys Ther, Epub 7 Dec 2018. doi:10.2519/jospt.2019.8541.