Full-Text Selection
After examination of 3320 titles and abstracts, 217 potentially relevant full-text articles were retrieved. After review of the full texts, 143 articles were excluded. The reference lists of the 74 remaining articles were checked, and 12 articles were added to the review [5, 16–26]. Hence a total of 86 articles were included in the review (Fig. 1).
Study Characteristics
Fourteen studies presented injury proportions for multiple populations of runners separately [17, 18, 27–38] and were classified into multiple populations of runners (Table 2). For track runners, injury proportions were reported for sprinters in 11 studies [17, 18, 27–32, 39–41], nine studies examined middle-distance runners [17, 18, 27–33] and six studies looked at injury proportions among long-distance track runners [17, 29–33]. Cross-country runners were studied in 21 articles [5, 6, 16, 19–22, 24, 26, 42–53], and long-distance runners were studied in 14 articles [3, 23, 34–38, 54–60]. Most studies were conducted among marathon runners (N = 23) [29–31, 34–36, 38, 61–74], while seven studies focused on ultra-marathon runners [37, 75–80]. Thirteen studies monitored injury occurrence among novice runners [25, 81–92]. The smallest number of studies was conducted in recreational non-competitive runners (N = 4) [7, 93–95].
Table 2 Study characteristics and injury proportions for the different populations of runners
Of the 86 included articles, 51 were prospective cohort studies [5–7, 16, 20–22, 24–31, 35, 36, 39–47, 49–53, 60, 69–72, 75–79, 81, 84–87, 91, 92, 95–97]. Of these, seven also included a retrospective injury proportion [6, 46, 50, 51, 53, 71, 72]. Twenty-four studies solely used a retrospective cohort design [3, 17–19, 23, 33, 34, 37, 38, 54–58, 61, 62, 64–67, 73, 74, 80, 94]. Five studies reported injury proportions cross-sectionally [32, 48, 59, 63, 93]—two of them retrospectively [59, 63]. From all included studies, nine reported injury incidence densities in addition to injury proportions [7, 27, 42, 44, 49, 78, 83, 88, 95]. Six articles reported the results of a randomized, controlled trial that reported injury occurrence [68, 82, 83, 88–90].
The follow-up periods of the included prospective cohort studies ranged from 1 day to 2 years. For retrospective cohort studies, the recall period varied from 1 day to a lifetime. A time-loss definition was used in 50 studies [3, 5–7, 16, 18, 20–28, 39–42, 44–46, 51, 54–58, 61, 62, 64–68, 71, 72, 74, 80–83, 86, 88–92, 94, 95]. Twenty studies used a medical-attention definition [17, 29–31, 35, 36, 60, 63, 69, 70, 75–79, 84, 85, 87, 96, 97], 11 registered pain-related injuries [6, 7, 16, 32, 49, 52, 53, 63, 73, 80, 93] and in 11 studies, the injury definition was not specified [19, 33, 34, 37, 38, 43, 47, 48, 50, 59, 62]. All study characteristics are presented in Electronic Supplementary Material Appendix S3.
Risk of Bias
The results of the ROB analysis can be found in Electronic Supplementary Material Appendix S4, and total ROB scores are presented in Table 2. The overall ROB of all included articles was 57.0 %, ranging from 0 to 100 %. Twenty-one articles with an ROB score below 50 were classified as having a high ROB [18, 19, 22, 23, 33, 34, 37, 38, 48, 50, 53, 55, 56, 59, 61–64, 66, 73, 80]. In general, lower ROB scores were the result of low scores on the following items of the ROB checklist: (1) the participation rate was less than 80 %; (2) demographics were missing/incomplete; and (3) the main objective of the study was not to examine injury proportions.
Meta-analyses of Injury Proportions
Fifteen studies reported injury proportions for specific conditions only [17, 28, 32, 33, 37, 39, 43, 46–49, 52, 59, 84, 87], so the results of those studies could not be pooled (Table 2). The results of the meta-analysis of all studies are shown in Figs. 2, 3, 4, 5 and 6. Heterogeneity was high, as indicated by the I
2 values that exceeded 50 % (Figs. 2, 3, 4, 5 and 6). The results of the sensitivity analysis (ROB ≥50) can be found in Electronic Supplementary Material Appendix S5. The results of the meta-analysis are described below for each follow-up/recall period and injury type.
Medical-Attention Injuries During an Event
Results were pooled from 22 study populations in which medical encounters during a running event were monitored (Fig. 2) [29, 31, 35, 36, 60, 63, 69, 70, 75–79, 96, 97]. The proportion of medical-attention injuries was highest in ultra-marathon runners [65.6 % (95 % CI 55.6–74.4)] and lowest in road runners [0.9 % (95 % CI 0.2–3.8)]. The injury proportions among elite track runners varied from 7.2 % (95 % CI 3.9–12.9) in sprinters to 12.8 % (95 % CI 7.0–22.3) in middle-distance runners and 15.6 % (95 % CI 11.2–21.2) in long-distance track runners. Medical-attention injuries during an event were not monitored in novice, recreational and cross-country runners. During a marathon race, a medical encounter was registered in 7.8 % (95 % CI 2.9–19.2) of runners. All studies followed runners for a single day, with the exception of most studies in ultra-marathon runners, which followed participants during multi-day competitions. The sensitivity analysis pooled 21 study populations (see Electronic Supplementary Material Appendix S5) [29, 31, 35, 36, 60, 69, 70, 75–79, 96, 97]; this analysis revealed identical results, except for those in marathon runners, who showed an injury proportion that was slightly higher [9.4 % (95 % CI 3.3–23.9)].
Time-Loss and Pain-Related Injuries During an Event
Five studies that included only long-distance road runners (N = 1) [54] and marathon runners (N = 4) [54, 61, 65, 71, 72, 74] assessed the occurrence of time-loss injuries during a race. The data from these studies were pooled. Participants in short road races reported a time-loss injury proportion of 28.4 % (95 % CI 26.0–31.0). Among marathon runners, the pooled time-loss injury proportion was 20.6 % (95 % CI 9.3–39.6). The sensitivity analysis of time-loss injuries during an event consisted of four studies [54, 65, 71, 72, 74]. The injury proportion among long-distance road runners was identical. The pooled injury proportion in marathon runners (N = 3) was 13.0 % (95 % CI 8.5–19.3).
Three studies among marathon runners examined the number of pain-related injuries during an event [63, 69, 73, 96]. The pooled estimate was 73.9 % (95 % CI 14.7–97.9). In the sensitivity analysis, one study remained, in which 92.4 % (95 % CI 90.4–94.0) of the participants reported a pain-related injury [69, 96].
Time-Loss and Pain-Related Injuries During a Short Follow-Up/Recall Period
Data were pooled from 15 study populations in which time-loss injuries were recorded during a short follow-up/recall period (Fig. 3) [5–7, 16, 20, 21, 42, 44, 45, 51, 62, 64, 82, 83, 86, 88–90, 92, 95]. No studies were conducted in track runners (sprint, middle-distance and long-distance) with a short follow-up/recall period. The pooled injury proportion was highest in marathon runners [64.7 % (95 % CI 25.6–91.2)] and lowest in cross-country runners [19.7 % (95 % CI 10.9–33.1)]. In these studies, cross-country runners were often prospectively followed during a cross-country season (of around 13 weeks).The pooled injury proportions were 26.4 % (95 % CI 14.2–43.7) in novice runners and 28.0 % (95 % CI 23.1–33.5) in recreational runners. Both studies among marathon runners were omitted from the sensitivity analysis [62, 64]; the other results did not change (see Electronic Supplementary Material Appendix S5).
Five studies examined the occurrence of pain-related injuries with a short follow-up/recall period (Fig. 4) [6, 7, 16, 53, 73]. The data from three studies of pain-related injuries among cross-country runners were pooled, resulting in the highest pooled injury proportion [47.3 % (95 % CI 44.6–49.9)] [6, 16, 53]. Pain-related injuries were registered in one study among recreational runners [34.5 % (95 % CI 30.9–38.3)] [7]. In marathon runners, one study monitored pain-related injuries, with an injury proportion of 36.6 % (95 % CI 31.9–41.6) [73]. The study in marathon runners [73] and a study in cross-country runners [53] were excluded from the sensitivity analysis (see Electronic Supplementary Material Appendix S5). The proportions of pain-related injuries among recreational runners were identical in the sensitivity analysis. The estimated injury proportions of pain-related injuries in cross-country runners remained similar [47.4 % (95 % CI 44.7–50.1)].
Time-Loss Injuries During a 1-Year Follow-Up/Recall Period
Nineteen studies that monitored time-loss injuries for a 1-year follow-up/recall period were pooled (Fig. 5) [18, 22–27, 40, 41, 57, 58, 65, 67, 68, 71, 72, 74, 80, 91, 94]. The pooled injury proportions were highest in sprinting athletes [63.8 % (95 % CI 56.5–70.5)] and middle-distance track runners [63.9 % (95 % CI 41.4–81.6)]. No data were available for long-distance track runners. The injury proportion was lowest in cross-country runners, at 3.2 % (95 % CI 0.9–10.5). One study that followed novice runners for a year reported a time-loss injury proportion of 27.3 % (95 % CI 24.5–30.3). One study retrospectively assessed 1-year time-loss injury occurrence in recreational runners [55.0 % (95 % CI 48.1–61.8)]. In long-distance road runners and marathon runners, the pooled injury proportions were 31.7 % (95 % CI 25.8–38.2) and 52.0 % (95 % CI 43.1–60.8), respectively. One study reported a 1-year time-loss injury proportion of 64.6 % (95 % CI 61.9–67.2) among ultra-marathon runners. The sensitivity analysis led to small differences in sprinters [62.8 % (95 % CI 54.4–70.4)], middle-distance runners [76.9 % (95 % CI 47.8–92.4)], cross-country runners [4.2 % (95 % CI 0.6–23.9)] and long-distance road runners [28.7 % (95 % CI 27.4–30.0)]. The injury proportions in novice and recreational runners were identical, and there were no studies in ultra-marathon runners (see Electronic Supplementary Material Appendix S5).
Time-Loss Injuries During a Long Follow-Up/Recall Period
Results were pooled from seven studies in which time-loss injuries during a long follow-up/recall period were monitored (Fig. 6) [3, 6, 51, 55, 56, 66, 81]. No studies were conducted among sprinting or middle- and long-distance track runners. One study prospectively followed novice runners during an 18-month running programme and reported an injury proportion of 84.9 % (95 % CI 74.8–91.5) [81]. Recreational runners were not studied over periods longer than a year. The pooled injury proportions in cross-country runners and long-distance road runners were 77.4 % (95 % CI 60.6–88.4) and 43.2 % (95 % CI 32.2–54.9), respectively. One study of marathon runners reported an injury proportion of 31.3 % (95 % CI 28.8–33.9) [66]. In the sensitivity analysis, three studies were removed from the analysis (see Electronic Supplementary Material Appendix S5) [55, 56, 66]. This increased the injury proportion among long-distance road runners to 52.5 % (95 % CI 48.3–56.7), and no information on marathon runners was available.
Anatomical Locations of Injuries
The site-specific injury proportions can be found in Electronic Supplementary Material Appendix S5. An overview of the site-specific time-loss injury proportions can be found in Fig. 7. The numbers of injuries sustained in the hip/pelvis region were similar for all populations of runners, with injury proportions ranging from 5.7 % in cross-country runners to 10.8 % in sprinting track athletes. Injury proportions in the upper leg were small for most populations of runners (5.5–9.0 %). In sprinting athletes, however, most injuries (32.9 %) occurred in the upper leg. The opposite was found for the knee region. Sprinters had the smallest number of injuries in the knee (1.3 %), while the injury proportions in the other populations varied from 22.5 % (in cross-country runners) to 30.6 % (in novice runners). Most injuries in recreational runners were reported around the knee (26.3 %). Novice runners (34.7 %), cross-country runners (30.3 %) and marathon runners (29.9 %) reported the most injuries in the lower leg. Sprinting athletes did not report ankle injuries; this range varied from 7.8 % (in recreational runners) to 16.2 % (in cross-country runners) in the other populations. Novice runners and sprinters reported foot injury proportions of 3.5 and 4.0 %, respectively. For cross-country runners (8.1 %), recreational runners (10.1 %) and marathon runners (13.1 %), the numbers of injuries in the foot were greater.