Three reviews on running injuries were published more than a decade ago.25,26,27
New studies on running injuries since those reviews have been incorporated into this systematic review. Further, in contrast to the methods used in those reviews, we undertook a systematic search strategy. We also evaluated the quality of the studies included and carried out a best evidence synthesis for determinants of lower extremity running injuries. Thus our review is a rigorous update of earlier reviews and provides evidence of risk factors for these injuries.
Incidence of injuries
The reported overall incidence of lower extremity running injuries showed a large range (19.4% to 79.3%). An increase in the incidence range is mainly seen in studies that also included non‐lower‐extremity injuries in their incidence numbers (19.4% to 92.4%), although higher incidences may partly reflect higher rate of lower extremity injury. Previous reviews reported ranges of 24% to 83%,26
33% to 85%,27
and 24% to 77%.28
The most common site of lower extremity injuries was the knee (7.2% to 50.0%), followed by the lower leg (9.0% to 32.2%), the foot (5.7% to 39.3%), and the upper leg (3.4% to 38.1%). Less common sites of lower extremity injuries were the ankle (3.9% to 16.6%) and the hip/pelvis (3.3% to 11.5%). Our results supports Van Mechelen's conclusion28
that most of running injuries are located in the knee.
What is already known on this topic?
- Besides its positive heath effects, running may also cause injuries, especially to the lower extremities. Various studies have reported on the prevalence and incidence of running injuries occurring in long distance runners during training or races. Risk factors contributing to the occurrence of these injuries have also been reported.
What this study adds
- The incidence of lower extremity running injuries in published reports ranges from 20% to 79%.
- The predominant site of these injuries is the knee.
- There is strong evidence that a long training distance per week in male runners and a history of previous injuries are risk factors for running injuries.
Determinants of injuries
Only limited evidence was found for some of the systemic, lifestyle, and health factors as risk factors for running injuries. These included greater age (a clear cut off point for greater age could not be observed), sex, lower leg length difference, greater left tubercle–sulcus angle and greater knee varus, greater height in male runners, drinking alcohol, participation in cycling and aerobics, and a positive medical history. We found strong evidence for a greater training distance per week in male runners and a history of previous injuries as a risk factor for both male and female runners. There was also strong evidence that increased training distance per week was a protective factor, although only for knee injuries. It remains unclear why increasing weekly distance is protective for knee injuries. However, the relation between distance and injury may not be simple and there may be a fine balance between overuse and underconditioning among long distance runners. For several other training/running related factors we only found limited evidence that they were risk factors (greater training frequency in male runners, running the whole year through, greater training distance in female runners, participation in races of greater distance, women running on concrete surfaces, competitive male runners, increase in days of training per week, increase in training distance per week, level of experience in running, use of more shoes for running, and shoe age).
Although limited evidence was found that greater weight and a body mass index of >26 kg/m2 were protective factors, this association may be caused by the fact that in these groups of runners less training activity is being undertaken.
Because of the specific search definition and because the language restriction we used to identify studies in the PubMed–Medline database, we may have found fewer studies on running related injuries than are available. In the studies identified there was a lack of standard definition of injury. In some studies running injuries were defined as running related injuries to the lower extremities, but other studies also included non‐lower‐extremity injuries and even problems such as headache, dehydration, fatigue, and others. Further, different study designs, differing data collection methods, and differing methods of determining the denominator might have affected the incidence rates of the studies. Also, the type of runners selected for each study varied—usually a specific selection of runners was made (for example, male runners, recreational runners, runners in training programmes, race participants). All these factors may have influenced the final incidence rates of injuries and the odds ratios and relative risks for the determinants.
We decided only to include studies that investigated long distance runners. The studies of Bennell et al9
and Lysholm and Wiklander13
both described a group of track and field athletes; however, they also described a separate group of long distance/marathon runners. Both these studies were included in our review because they described the results of the long distance runners separately from the whole track and field athletes group; thus only the results for the long distance runners were included in this study.
The results could also be biased by a self selection process of healthy runners participating in running events or training programmes in the studies included, or by injured runners not responding to questionnaires or overreporting of injuries because of the self reporting nature of some studies.
For some subgroups reported here, there was low power. This might have influenced our conclusions, based on the best evidence synthesis. For example, associations were found for male but not female runners, while the estimate of the association in both sexes was the same. This probably reflects a reduced statistical power in the female subgroup.
Fortunately, 12 studies reported the sites where the lower extremity running injuries occurred. Specific diagnoses, however, were discussed in only three studies and not even for all injured runners.10,11,20
Also the impact of these running injuries was rarely reported. Very little information was provided on the duration and severity of these injuries, and there was a lack of information about health care visits (for example, to general practitioner, physiotherapist, orthopaedic specialist) or the treatment used (drugs, rest, operation, other).
The presence of associations between determinants and running injuries suggests that advice and education may still be necessary. An unmodifiable risk factor is a history of previous injuries. Runners with this risk factor should pay extra attention to signs of injuries, avoid other determinants of injuries, and take time to recover fully from their injuries. The training distance per week is a modifiable risk factor and therefore runners should preferably not exceed 64 km/week.
Further investigation is necessary, because the incidence of running injuries in long distance runners is not clear and knowledge of the specific determinants of these injuries is still unsatisfactory. Future studies should clearly define the type of runners included (sprinters, middle distance, or long distance runners) and also specifically report information about training characteristics and race participation, so that the results can be applied on the correct group of runners. Also investigators should try to use a universal definition of running injury, so that results can easily be compared.
Likewise the length of observation period needs to be equal in different studies and the incidence numbers need to be expressed in comparable units.
Finally, to obtain information on the clinical consequences of running injuries, details on the duration and severity of these injuries, as well as information on the use of professional medical advice and the chosen treatment, is required.