Factors Associated With Running-Related Injuries in Recreational Runners With a History of Running Injuries

Supplemental Digital Content is Available in the Text.

Abstract

Objective:

To identify the incidence and characteristics associated with a higher injury risk in recreational runners who suffered a running-related injury (RRI) in the previous 12 months.

Design:

Prospective cohort study among recreational runners who registered for a Dutch running event (5-42.2 km) and suffered an RRI in the 12 months before inclusion.

Setting:

Open population.

Participants:

Recreational runners with a previous reported injury.

Assessment of Risk Factors:

At baseline, information on demographics, training characteristics, health complaints, and RRI history was collected.

Main Outcome Measures:

With 3 follow-up questionnaires (2 weeks before, 1 day after, and 1 month after the running event), the occurrence of new RRIs was registered.

Results:

In total, 548 participants (55.1%) sustained a new RRI during follow-up. In total, 20.5% of the new RRIs was located at the same anatomical location as the previous RRI. Runners who registered for a marathon had a higher chance to sustain a new RRI [odd ratio (OR) 1.72; 95% confidence intervals (CIs), 1.17-2.53]. Also previous RRIs in the upper leg (OR 1.59; 95% CI, 1.15-2.19) and lower leg (OR 1.61; 95% CI, 1.18-2.21) were associated with an increased injury risk.

Conclusions:

Especially being a marathon runner and the anatomical location of previous RRIs seem to be associated with the injury risk in recreational runners with a previous RRI.

INTRODUCTION

Running is a popular sport that has many health benefits.¹ However, injuries are a major problem among runners. In 2018, 14% of all Dutch sports injuries were sustained by runners, which makes running as one of the 3 sports with most injuries in the Netherlands.² Scientific literature describes high variability in incidence rates of running-related injuries (RRIs), ranging from 3.2% to 84.9%.³ The high incidence rates indicate the necessity for RRI prevention in recreational runners.

In 1992, Van Mechelen et al⁴ introduced the sequence of prevention model, which describes 4 steps for the development of injury prevention measures. In accordance with the second step of this model, several studies investigated the factors and mechanisms associated with a new RRI.^5,6 Many different factors associated with an increased injury risk were identified in literature (eg running frequency, sex, and use of orthotics). However, results are often conflicting. A systematic review showed, for example, that a higher age was associated with more RRIs in some studies, whereas it was associated with less RRIs in another study.⁶ Only a previous RRI is in literature consistently identified as a factor associated with an increased risk for RRIs.^5–7

Even though runners who suffered an injury in the past have a higher chance to sustain a new RRI, characteristics of these runners with new RRIs in a relatively short time frame are, to our best knowledge, not yet investigated. Insight in the characteristics associated with RRIs in this specific population may, however, yield useful information for future prevention of RRIs. Therefore, the aim of this study was to examine the incidence and characteristics associated with new RRIs in recreational runners who suffered an RRI in the previous 12 months.

MATERIALS AND METHODS

This study was performed with data of the Intervention Study on Prevention of Injuries in Runners at Erasmus MC (INSPIRE) trial, a randomized-controlled trial on the effectiveness of an injury prevention program for runners, with a minimum follow-up of 3 months [mean (SD) follow-up duration was 4.5 (1.6) months].^8,9 Because the injury prevention program was not effective, the INSPIRE trial can be regarded as a prospective cohort study for the current study purpose.⁹ Potentially eligible participants of the current study were recreational runners, aged 18 years and older, who registered for one of the 3 selected running events (distances 5-42.2 km) in 2017 and suffered an RRI in the 12 months before inclusion in the study. Furthermore, only runners who filled out at least one of the follow-up questionnaires were included.

The INSPIRE trial was funded by the Netherlands Organisation for Health Research and Development (ZonMW, grant number 536001001) and performed in collaboration with the Rotterdam Marathon Study Group of Golazo Sports, an organizer of large running events in the Netherlands. The study was approved by the medical ethical committee of the Erasmus MC University Medical Center Rotterdam (MEC-2016-292), and all participants provided digital informed consent before participating.

At registration for the running event, participants were asked to complete the baseline questionnaire. This questionnaire consisted of questions on possible predictive factors and was divided into 5 categories (demographics, training, running events, lifestyle, and previous RRIs). The items of the sections are listed in Table 1. The occurrence of new RRIs was evaluated with 3 follow-up questionnaires (2 weeks before, 1 day after, and 1 month after the running event the runners registered for). All follow-up, questionnaires obtained information on the presence of new RRIs (yes/no) and the location of the new injuries (lower back/buttock/hip/groin/ventral thigh/dorsal thigh/knee/shin/calf/Achilles tendon/ankle/foot/toe).

TABLE 1.

Possible Risk Factors for New Running-Related Injuries

Section	Items
Demographics	Sex
	Age (yr)
	Height (cm)
	Weight (kg)
Training	Running experience (yr)
	Average running distance over the last month (km/wk)
	Average training speed over the last month (min/km)
	Use of training schedules (yes/no)
	Type of training:
	Endurance training (%)
	Interval training (%)
	Specific exercises (%)
	Use of compression socks (yes/no)
	Use of inlays (yes/no)
Running event	Distance of running event (km)
Lifestyle	Average alcohol consumptions (glasses/wk)
	Participation in other sports (yes/no and type)
	Other health problems (yes/no and type)
Running-related injuries	Location of previous running injury (lower back/buttock/hip/groin/ventral thigh/dorsal thigh/knee/shin/calf/Achilles tendon/ankle/foot/toe)
	Still suffering running injury (yes/no)

Body mass index was calculated using height and weight. Alcohol consumption and types of training (percentages of endurance training, interval training, and specific exercises) were categorized with the mean as cut-off value when normally distributed and the median as cut-off value when nonnormally distributed. The sports practiced besides running were divided into sports with and without axial loading.¹⁰ Sports with axial loading were defined as sports that presented a direct vertical force of at least one time body weight between the ground and the lower extremities. Other health complaints were divided into musculoskeletal disorders (eg, osteoarthritis, back problems, and gout), cardiovascular disorders, and other comorbidities (such as allergies, epilepsy, and skin problems). The anatomical locations of both the previous and the new RRIs were clustered into lower back, upper leg (including buttock, hip, groin, and ventral and dorsal thigh), knee, lower leg (including shin, calf, Achilles tendon, and ankle), and feet (including feet and toes).

The primary outcome measure of this study was a new RRI sustained during follow-up. An RRI was defined as an injury of the muscles, joints, tendons, and/or bone in the lower back or lower extremities that was caused by running.⁸ Furthermore, one of the following criteria had to be met:

1. The injury was severe enough to cause a reduction in training distance, speed, duration, or frequency for at least 1 week

2. The injury led to visiting a doctor and/or physiotherapist

3. Medication was necessary to reduce symptoms as a result of the injury.

The clustered anatomical location of the new RRI was a secondary outcome measure.

Descriptive statistics were used to present frequencies and percentages for categorical data and mean and SD for numeric data. To check for selection bias, baseline characteristics of participants who completed at least one follow-up questionnaire (and were consequently included in the analyses) were compared with those of participants who did not. These comparisons were made using independent t test, Mann–Whitney U test, and χ² test. The injury proportion of the included runners was calculated as the percentage of runners who reported a new RRI in one of the follow-up questionnaires. To correct for errors, we checked whether participants who indicated they still suffered an existing RRI indeed filled in an RRI on the same location in the previous questionnaire. If not, the RRI was interpreted as a new RRI. Also for RRIs of which participants indicated to be new, we checked whether the participants did not fill in this RRI in the previous questionnaire. Using univariate and multivariable logistic regression analyses, the associations between a new RRI during follow-up and potential predictive factors were determined, using the possible predictive characteristics presented in Table 1. All variables with a P-value <0.20 were consequently entered in a multivariable (backward selection) logistic regression model. Results were presented as odds ratios (OR) and 95% confidence intervals (95% CIs). All analyses were performed in SPSS Statistics V.25 (Chicago, IL), and P-values below 0.05 were considered statistically significant.

RESULTS

Of the 2378 recreational runners included in the INSPIRE trial, 1238 runners reported that they suffered an RRI in the 12 months before the start of the study. A total of 994 (80.3%) of them completed at least one of the follow-up questionnaires and were consequently included in the present study. Some differences were seen between the included and excluded runners, that is, the included runners were on average older, had a lower body mass index, performed more interval training, and used inlays more often than the excluded runners (see Supplementary Data File, Supplementary Digital Content 1, http://links.lww.com/JSM/A327). Furthermore, the included runners consisted of relatively more half-marathon runners, and the excluded runners of more marathon runners.

At baseline, the mean age of the included runners was 42.2 (SD 11.7, inter quartile range 19) years and the majority (55.4%) was male (Table 2). Almost half of the participants (41.8%) still suffered from their previous RRI at baseline.

TABLE 2.

Baseline Characteristics of the Participants

	All Participants		New Injury during Follow-up		No New Injury during Follow-up
	N	%/Mean (SD)	N	%/Mean (SD)	N	%/Mean (SD)
N	994		548		446
Sex (male)	551	55.4%	315	57.5%	236	52.9%
Age (yr)		42.2 (11.7)		42.6 (11.5)		41.7 (11.9)
BMI (kg/m2)		23.5 (2.7)		23.5 (2.7)		23.5 (2.7)
Running experience (yr)*		6.8 (8.1)		6.8 (8.4)		6.6 (7.7)
Running distance per wk (km)		23.1 (18.7)		23.7 (18.2)		22.3 (19.3)
Training speed (min/km)†		6:02 (1:02)		5:59 (1:01)		6:04 (1:03)
Type of training (%)
Endurance training		67.7 (23.5)		66.9 (23.2)		68.6 (23.8)
Interval training		24.7 (20.5)		25.0 (20.1)		24.2 (21.0)
Exercises		7.7 (9.7)		8.1 (10.1)		7.2 (9.2)
Distance of the running event
5/7.5 km	45	4.5%	21	3.8%	24	5.4%
10/10.55 km	373	37.5%	187	34.1%	186	41.7%
Half-marathon	316	31.8%	175	31.9%	141	31.6%
Marathon	263	26.5%	168	30.7%	95	21.3%
Participation in other sport
Axial sport	230	23.1%	129	23.5%	101	22.6%
Nonaxial sport only	387	38.9%	221	40.3%	166	37.2%
Other health problems
Musculoskeletal system	38	3.8%	18	3.3%	20	4.5%
Cardiovascular disease	59	5.9%	27	4.9%	32	7.2%
Other	100	10.1%	56	10.2%	44	9.9%
Use of training schedules (yes)	648	65.2%	374	68.2%	274	61.4%
Use of compression socks (yes)	196	19.7%	122	22.3%	74	16.6%
Use of inlays (yes)	266	26.8%	154	28.1%	112	25.1%
Alcohol consumption (glasses/wk)		4.3 (5.0)		4.1 (4.8)		4.5 (5.3)
Anatomical location previous RRI
Back	130	13.1%	82	15.0%	48	10.8%
Upper leg	314	31.6%	194	35.4%	120	26.9%
Knee	392	39.4%	209	38.1%	183	41.0%
Lower leg	488	49.1%	288	52.6%	200	44.8%
Feet	164	16.5%	86	15.7%	78	17.5%
Reported RRI at baseline (yes)	415	41.8%	236	43.1%	179	40.1%

^*Running experience is missing for 6 participants.

^†Training speed is missing for 34 participants.

BMI, body mass index.

During follow-up, 548 participants (55.1%) sustained in total 940 new RRIs (Table 2). Most RRIs were located in the lower leg (34.9%), upper leg (27.9%), and the knee (19.3%). Furthermore, 20.5% of the new RRIs was located at the same anatomical location as the previous injury. This was most seen in the calf, knee, and dorsal thigh, where, respectively, 26.9%, 25.0%, and 25.0% of the runners with a new injury had an injury at the same anatomical location before.

Registration for a marathon (OR 1.78; 95% CI, 1.29-2.46), the use of a training schedule (OR 1.35; 95% CI, 1.04-1.75), the use of compression socks (OR 1.44; 95% CI, 1.05-1.98), and a previous RRI located in the upper leg (OR 1.49; 95% CI, 1.13-1.96) and lower leg (OR 1.36; 95% CI, 1.06-1.75) were significantly associated with a new RRI in the univariate logistic regression analyses (Table 3). The results of the multivariable logistic regression analysis showed that injuries occurred more often in runners who registered for a marathon compared with runners who registered for a 10- or 10.55-km running event (OR 1.73; 95% CI, 1.24-2.39), had a previous RRI located in the upper leg (OR 1.62; 95% CI, 1.22-2.16), or had a previous injury in the lower leg (OR 1.51; 95% CI, 1.16-1.97). The other baseline characteristics were not associated with the occurrence of a new RRI.

TABLE 3.

Univariate and Multivariable Logistic Regression Analyses of Potential Risk Factors for New Running-Related Injuries During Follow-up

Variable	Univariate Analysis	Multivariable Analysis*
	OR (95% CI)	OR (95% CI)
Sex (female)	0.83 (0.65-1.07)
Age (yr)	1.01 (1.00-1.02)†
BMI (kg/m2)	0.99 (0.95-1.04)
Running experience (yr)	1.00 (0.99-1.02)
Running distance per wk (km)	1.00 (1.00-1.01)
Training speed (s/km)	1.00 (1.00-1.00)
Type of training
Endurance training (>68%)	0.95 (0.74-1.22)
Interval training (>25%)	1.04 (0.80-1.34)
Exercises (>5%)	1.18 (0.91-1.52)
Distance of the running event
5/7.5 km	0.80 (0.42-1.50)	0.83 (0.44-1.58
10/10.55 km	Reference	Reference
Half-marathon	1.25 (0.92-1.69)	1.22 (0.90-1.65)
Marathon	1.78 (1.29-2.46)‡	1.73 (1.24-2.39)‡
Participation in other sport
Axial sport	1.16 (0.83-1.61)
Nonaxial sport only	1.20 (0.91-1.60)
No other sport	Reference
Other health problems
Musculoskeletal system	0.72 (0.38-1.39)
Cardiovascular disease	0.67 (0.40-1.14)†
Others	1.04 (0.69-1.58)
Use of training schedules (yes)	1.35 (1.04-1.75)‡
Use of compression socks (yes)	1.44 (1.05-1.98)‡
Use of insoles (yes)	1.17 (0.88-1.55)
Alcohol consumption (>3 glasses/wk)	0.94 (0.73-1.21)
Location previous RRI
Back	1.46 (1.00-2.14)†
Upper leg	1.49 (1.13-1.96)‡	1.62 (1.22-2.16)‡
Knee	0.89 (0.69-1.14)
Lower leg	1.36 (1.06-1.75)‡	1.51 (1.16-1.97)‡
Feet	0.88 (0.63-1.23)
Reported RRI at baseline	1.13 (0.88-1.45)

^*Only variables with P < 0.20 in univariate analyses were entered in the multivariable backward selection model.

^‡P < 0.05.

^†P < 0.20.

BMI, body mass index.

DISCUSSION

The aim of this study was to determine the incidence and characteristics associated with RRIs in recreational runners who suffered an RRI in the previous 12 months. The results showed that 55.1% of the runners who suffered an injury in the 12 months before the study sustained a new RRI during follow-up. In total, 20.5% of the new RRIs was located at the same anatomical location as the previous RRI. Registration for a marathon event and a previous injury in the upper or lower leg were associated with a higher risk of new injuries in these previously injured runners.

During preparation for a marathon, most runners train with a high weekly training distance. In previous studies, this variable was associated with an increased RRI risk.^6,11 Therefore, the high weekly training distance may explain why we found an association between registration for a marathon and a new RRI. However, no direct relation between weekly training distance and RRI risk was identified in the current study. This may be because weekly training distance was retrieved from the baseline questionnaire, which the participants completed at registration for the running event. Registration for the marathon opened more than 6 months before the actual marathon and therefore weekly training distance at registration was probably not as high as the last month before the marathon. This is supported by additional analyses that showed that most RRIs were sustained in the last weeks before the marathon (between follow-up questionnaire 1 and 2). During this period, 3.2 marathon runners sustained a new RRI per day compared with only 0.8 marathon runners per day between the baseline and the first follow-up questionnaire. Another factor that may impact the association between registration for a marathon and RRI risk is that the number of people who run a marathon strongly increased over the last years. As an example, 15 450 runners started the Rotterdam Marathon in 2017 compared with only 200 runners in 1981. Anecdotal information showed that marathons were mostly ran by experienced runners in the past. Nowadays, running a marathon is on the wish list of many people. Next to more experienced runners, relatively unexperienced runners also intend to run a marathon. In the present study, the average running experience of the marathon runners [7.7 (SD 8.7) years] was comparable with the running experience of the half-marathon runners [7.8 (SD 8.7) years] and only 2 years more than the 5/7.5 km [5.2 (SD 6.7) years] and 10/10.55 km [5.4 (SD 7.0) years] runners. Relatively unexperienced runners are known to have an increased injury risk.¹² Together with a high training volume during preparation for a marathon, this may explain why an association between registration for a marathon and a new injury was found. Moreover, runners who register for a marathon work toward a clear goal (the marathon), often with set training schedules. Runners therefore may ignore pain during running to reach this goal. This is supported by de Jong et al who showed that runners with obsessive passion for running, that is, a strong inclination where the runner feels compelled to engage in running, are more likely to report an RRI.¹³ This assumption is also supported by our own data in the univariate association between the use of training schedules and injury risk. To reach their goal, runners may also restart running too fast after an RRI, which may increase the chances of getting reinjured.^14,15

Previous injuries are in literature consistently found to be associated with an increased risk for RRIs.^5,6 Within this group of runners who suffered an RRI in the previous year, our results seem to indicate that some anatomical locations of this previous injury seem to increase the risk of new injuries. Runners with a previous lower or upper leg injury had a 1.6 times higher injury risk compared with runners with previous injuries at other locations, although the exact diagnoses and affected structures are unknown. Although causal assumptions are hard to draw, recovery of previous injuries may play an important role in this population of previously injured runners. Previous research has shown that calf and anterior thigh injuries recover relatively fast compared with injuries at other anatomical locations.^16,17 This may result in a quick return to running with high loading demands that may potentially lead to a new injury. In the current study, the calf and dorsal thigh were among the 3 injury locations at which the new RRI was most often at the same anatomical location as the previous injury. This may indicate that these injuries tend to recur more often because most runners will start running soon with too much external load, and therefore, they might be at increased risk for a reinjury. However, with the data of the current study, we can only speculate about the underlying mechanisms of the increased RRI risk after an upper or a lower leg injury. To draw firm conclusions, more research on the diagnosis and recovery from upper and lower leg injuries and the restart of running after these injuries is necessary. More insight in, for example, the recovery of the underlying muscle or tendon damage of upper and lower leg injuries in relation to pain symptoms may help runners to decide when to restart running.

To our best knowledge, this is the first study that investigated characteristics associated with new RRIs in recreational runners who suffered an RRI in the previous 12 months. Strengths of this study include the large sample size and the relatively small loss to follow-up rate. However, there are some limitations that should be taken into account when interpreting the results of this study. A first limitation is that we did not study risk factors for RRIs in runners who did not suffer a previous injury in the last 12 months. Therefore, we cannot compare the risk factors for runners with and without previous injuries. Furthermore, 41.8% of the included participants were injured at baseline, which affected the results. Sensitivity analysis showed that the results of the risk factors slightly changed when excluding runners who were injured at baseline. These changes were mainly due to power issues, and the direction and magnitude of the ORs were similar to those of the presented analysis. Another limitation is that self-reported RRIs were used as primary outcome measure. Even though we provided the participants with our definition of an RRI in all questionnaires, the self-reported RRIs are susceptible to interpretation of the runners. Also, the clustering of the injury locations may be a limitation. If we would not have clustered the injury locations or have chosen a different clustering, the results of the current study may have been different. Furthermore, some recall bias may exist as the baseline questionnaire and the first follow-up questionnaire were several months apart. The exact moment at which the runners sustained an RRI was also unknown and therefore it was impossible to perform analyses with a time-varying component. Finally, some significant differences in characteristics existed between the runners who filled out at least one follow-up questionnaire (and were consequently included in the current study) and runners who did not complete the follow-up questionnaires. Therefore, the results of the present study mainly apply to relatively older and fitter runners, who more often registered for a half-marathon.

CONCLUSIONS

This study investigated the incidence and characteristics of runners associated with an increased RRI risk in runners who suffered an injury in the past 12 months. The incidence of new injuries is high among previously injured runners and marathon runners and runners who previously had an upper or lower leg injury had an increased injury risk. The results of the present study indicate that marathon runners who suffered an RRI in the previous 12 months should be aware of their increased injury risk. Also, runners, trainers, and health care providers should be aware of the increased injury risk of runners with a previous injury in the upper or lower leg and be cautious with the restart of running. More research on underlying mechanisms and causality is necessary to start preventive interventions.

Supplementary Material

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