Both competitive and recreational runners are increasingly using GPS watches and smartphone apps that collect large amounts of training data. Many online programs use these data to provide training guidance, which claims to improve running performance and prevent injuries. While increasing training volume has been identified as a modifiable risk factor for running-related injury in multiple studies, data collected by GPS watches and smartphones have yet to be used to identify patterns associated with injury in marathon runners (1). In this blog, we share how we evaluated the training patterns of marathon runners using data collected by commonly used technology and associated these patterns with injury (2). 

Image: NYC marathon. Taken by Brett Toresdahl

Why is this study important?

Running is one of the most popular forms of exercise globally and has numerous health benefits (3). However, it also carries a risk of injury, regardless of age and experience level (4). Injuries are of particular concern when training for a marathon where injury incidence ranges from 30-58% and up to 15% of runners stop training due to injury (5-7). Despite numerous attempts to prevent injuries in runners, few interventions have proven effective (8-10). Training errors such as increasing volume too quickly or inconsistent training are thought to contribute to the development of running-related injuries. The “10% rule” (see below) is often used by sports medicine professionals to advise runners on how to increase their training volume, but there is no evidence supporting its effectiveness in preventing injury (10). 

How was the study performed?

Our study was a collaboration between Hospital for Special Surgery, New York Road Runners (organizer of the TCS New York City Marathon), and Strava. It was a prospective observational study of adult runners of the 2019 New York City Marathon. Runners were recruited through an email sent to all marathon registrants. Participants completed a baseline survey that included demographics, base running volume, race experience, and race goals. They were instructed to track all training runs using Strava, which is a free web and smartphone platform that can record training activities and sync with GPS watches. The 16 weeks before the marathon were subdivided into 4 training quarters. At the end of each quarter, participants completed a survey where they verified that their training log on Strava was complete and reported any injury or illness that affected training. Training patterns were evaluated with two commonly used methods of measuring changes in training volume:

(1) The “10% rule” (change in weekly distance not to exceed +10%):

(2) Acute:chronic workload ratio (ACWR, 7:28 coupled rolling average):

A logistic regression model was used to identify factors associated with injuries.

What did the study find?

We analyzed data from 735 runners who verified at the end of each training quarter that their Strava training logs were complete. Average age was 41 years, 46% were female, and 19% were first-time marathon runners. They logged a cumulative 49,195 runs during the 16-week study. The incidence of injury during training was 40%, with 4% experiencing an injury that prevented them from participating in the marathon. Uninjured runners averaged 4 runs per week and 28-34 miles per week during training. Age, sex, BMI, finishing time goal, base running volume, and race experience were not found to be associated with injury. Similarly, the number of weeks per training quarter when the 10% rule was exceeded was also not associated with injury. However, the number of days per training quarter when ACWR was ≥1.5 was associated with injury in both the univariable and multivariable analyses (univariable odds ratio, OR, 1.06 [95% confidence interval 1.03 to 1.10], multivariable OR 1.06 [1.02 to 1.10]).

What are the key take-home points? 

Injuries are common among runners training for a marathon. We found that the only factor consistently associated with injury was a rapid increase in training volume as measured by the number of days that the ACWR was ≥1.5. Interestingly, other previously described risk factors for running-related injury were not associated with injury in this population of runners, including age, sex, body mass index, and experience. The results suggest that consistent training with a gradual increase in volume may reduce the risk of injuries in marathon runners. The average training pattern of uninjured runners is also of note as this differs from many published marathon training plans. An opportunity exists for sports medicine professionals to use the training data currently being collected by runners to create a training program to guide runners more safely on increasing training, such as in preparation for a marathon.

Authors: Brett Toresdhal (ToresdahlB@hss.edu) & Jordan Metzl

References 

1. Damsted C, Glad S, Nielsen RO, Sorensen H, Malisoux L. Is There Evidence for an Association between Changes in Training Load and Running-Related Injuries? A Systematic Review. Int J Sports Phys Ther. 2018;13(6):931-942.
2. Toresdahl BG, Metzl JD, Kinderknecht J, et al. Training patterns associated with injury in New York City Marathon runners. Br J Sports Med. 2022.
3. Hulteen RM, Smith JJ, Morgan PJ, et al. Global participation in sport and leisure-time physical activities: A systematic review and meta-analysis. Prev Med. 2017;95:14-25.
4. Saragiotto BT, Yamato TP, Hespanhol Junior LC, Rainbow MJ, Davis IS, Lopes AD. What are the main risk factors for running-related injuries? Sports Med. 2014;44(8):1153-1163.
5. Clough PJ, Dutch S, Maughan RJ, Shepherd J. Pre-race drop-out in marathon runners: reasons for withdrawal and future plans. Br J Sports Med. 1987;21(4):148-149.
6. Toresdahl B, McElheny K, Metzl J, et al. Factors associated with injuries in first-time marathon runners from the New York City marathon. Phys Sportsmed. 2021:1-6.
7. Vitez L, Zupet P, Zadnik V, Drobnic M. Running Injuries in the Participants of Ljubljana Marathon. Zdr Varst. 2017;56(4):196-202.
8. Toresdahl BG, McElheny K, Metzl J, Ammerman B, Chang B, Kinderknecht J. A Randomized Study of a Strength Training Program to Prevent Injuries in Runners of the New York City Marathon. Sports Health. 2020;12(1):74-79.
9. Fokkema T, de Vos RJ, van Ochten JM, et al. Online multifactorial prevention programme has no effect on the number of running-related injuries: a randomised controlled trial. Br J Sports Med. 2019;53(23):1479-1485.
10. Buist I, Bredeweg SW, van Mechelen W, Lemmink KA, Pepping GJ, Diercks RL. No effect of a graded training program on the number of running-related injuries in novice runners: a randomized controlled trial. Am J Sports Med. 2008;36(1):33-39.