Objectives There is no consensus on the aetiology and prevention of running-related injuries in runners. Preconditioning studies among different athlete populations show positive effects on the incidence of sports injuries.
Hypothesis A 4-week preconditioning programme in novice runners will reduce the incidence of running-related injuries.
Study design Randomised controlled clinical trial; level of evidence, 1.
Methods Novice runners (N=432) prepared for a four-mile recreational running event. Participants were allocated to the 4-week preconditioning (PRECON) group (N=211) or the control group (N=221). The PRECON group started a 4-week training programme, prior to the running programme, with walking and hopping exercises. After the 4-week period both groups started a 9-week running programme. In both groups information was registered on running exposure and running-related injuries (RRIs) using an internet-based running log. Primary outcome measure was RRIs per 100 runners. An RRI was defined as any musculoskeletal complaint of the lower extremity or lower back causing restriction of running for at least a week.
Results The incidence of RRIs was 15.2% in the PRECON group and 16.8% in the control group. The difference in RRIs between the groups was not significant (χ2=0.161, df=1, p=0.69).
Conclusion This prospective study demonstrated that a 4-week PRECON programme with walking and hopping exercises had no influence on the incidence of RRIs in novice runners.
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Recreational and competitive running is very popular worldwide and the number of runners is ever-increasing. Running is an easy sports activity to maintain an active healthy lifestyle, and has beneficial effects on cardiorespiratory fitness, weight control and mental health.1 Sooner or later, however, many novice, recreational or competitive runners sustain injuries. The incidence of running-related injuries (RRIs) is high. Incidence rates vary from 20.3% to 84.9% and from 3 to 59 RRIs per 1000 h of running.2–6 Most RRIs are overuse musculoskeletal injuries of the lower extremity.3 ,4 ,7–11
The aetiology of RRIs is multifactorial and diverse. Various purported intrinsic and extrinsic risk factors for RRIs have been studied, but most studies on these factors show inconsistent or conflicting results.11 ,12 There is evidence that a greater weekly training distance, history of previous injuries, lack of running experience and running to compete are risk factors for lower-extremity running injuries.12 ,13 Hreljac states that many, if not all, running injuries are caused by training errors.14
Van Mechelen's opinion that the prevention of RRIs is primarily based on trial and error is still valid.15 So far, little high-quality research has been done on the prevention of RRIs in novice or recreational runners.4 Studies on the effects of interventions to prevent RRIs have methodological shortcomings, hence the continued need for controlled trials to shed light on such interventions.16
Buist et al17 showed that previous sports participation without axial loading (ie, swimming and cycling) was an important predictor for RRIs in novice runners in contrast with sports with axial loading (ie, soccer, hockey, basketball and volleyball). From this observation it can be hypothesised that a lack of previous participation in sporting activities without axial loads is a risk factor for sustaining an RRI. Milgrom18 found that the type of physical activity of recruits prior to military induction was a major determinant for stress fracture risk in basic training.
In a healthy situation the musculoskeletal system can adapt to mechanical loading and physical activity.19 ,20 These mechanotransduction mechanisms converts mechanical forces into biochemical events in musculoskeletal tissue in a loading-magnitude-dependent manner.19 ,20 When an optimal level of load is applied to the musculoskeletal system, its strength will increase given adequate recovery time. When loading is too high or the recovery time is too short however, the musculoskeletal system will be weakened and the likelihood of sustaining an overuse injury is increased.14 ,19 ,20
Novice runners are frequently inactive before they start running,3 ,17 ,21 and therefore their musculoskeletal systems are not used to the repetitive and high-impact forces of running.14 In most running programmes the biomechanical load is high from the start. When the musculoskeletal system of the novice runner cannot cope with this high load an RRI will occur.14 The GRONORUN 2 study was designed based on this knowledge.
The GRONORUN 2 study tests the effect of a preconditioning (PRECON) programme on RRIs in novice runners. In a PRECON programme the body is being prepared for regular high-intensity training by exposing it to a sport-specific load that will gradually increase in time. Athletes often participate in a PRECON programme before a competitive season or a regular training period. A small number of studies among athletic and military populations’ positive effects of PRECON programmes22–28 in preventing sport-specific injuries. No study has yet investigated the link between PRECON programmes and RRIs in novice runners.
In the present randomised controlled trial a PRECON programme was introduced in which novice runners prepared their body gradually for a high running load by doing walking and hopping exercises. The aim of the GRONORUN 2 study was to determine the effect of this PRECON programme on the incidence of RRI among novice runners. It was hypothesised that the lower extremity would positively adapt to the applied load and therefore the number of RRIs should decrease in the group receiving the PRECON programme.
The GRONORUN 2 study is a two-arm randomised controlled trial with a 4-week PRECON programme and a 9-week running programme. The GRONORUN 2 study was registered under NTR1906, in the Netherlands Trail Register (NTR). The NTR is part of the WHO Primary Registries. The design of the study is described more extensively elsewhere.29 The study design was approved by the Medical Ethics Committee of University Medical Center Groningen, The Netherlands under number (No. 2007.217). Guidelines according to the Consort Statement were followed.30
Participants, randomisation and baseline measurements
Healthy participants willing to prepare a recreational 4-mile run with a beginners’ 9-week training programme, were recruited with advertisements in the local media in the Northern part of the Netherlands. Participants aged between 18 and 65 who had not sustained an injury of the lower extremity in the last 3 months before inclusion and who had not been running on a regular basis in the previous 12 months were eligible for inclusion in the study. Participants were excluded when absolute contraindications for vigorous physical activities were present according to the American College of Sports Medicine.31
After baseline measurements and informed consent, participants were randomly assigned drawing an opaque envelope to the PRECON group or the control group. To ensure that both training groups were equal in terms of a priori injury risk, a stratified randomisation was performed. Participants were stratified for current sporting activities (no sport or axial or no axial sport), previous injuries (yes or no) and gender (male or female).
Participants had to fill in an internet-based baseline questionnaire.29 All participants were seen by an experienced sports physician to screen for cardiovascular disease and abnormalities of the lower limb, to ensure that the participants were eligible for the GRONORUN 2 study.29
Preconditioning programme (4 weeks)
Participants in the PRECON group took part in a 4-week individual PRECON programme (table 1). More information on PRECON programme can be found elsewhere.29
Nine-week running programme and running log
Directly after the 4-week PRECON programme, the 9-week running programme started in which all subjects participated (table 2). Information on RRIs and exposure data was collected using an internet-based running log. Detailed information on the running programme and running log can be found elsewhere.29
The primary outcome measure of the GRONORUN 2 trial was RRIs per 100 runners. An RRI was defined as any musculoskeletal complaint of the lower extremity or back causing a running restriction for at least 1 week. Exposure time was defined as the time (in minutes) a subject had been running in the 9-week programme. Time spent on walking and hopping was not calculated as exposure time.
Power analysis and statistics
Sample size was calculated for the main outcome variable, that is, RRI, using a logistic rank survival power analysis. As stated before, the incidence of RRIs varies between 20.3 and 84.9. A reduction of 25% on the incidence of RRIs in the PRECON group is considered clinically significant and relevant. The expected incidence of RRIs is 40%. With a hypothesised 25% reduction of RRIs in the PRECON group compared with the control group, a total of 360 runners (2×180) were needed for a power of 80% and an α of 0.05. Assuming an attrition rate of 15% in the PRECON period and follow-up period, a total of 414 (2×207) novice runners are needed to detect an effect of the 4-week PRECON programme.
Self-assessed baseline characteristics from participants with exposure in the 9-week running programme were compared between groups using two-tailed t-tests for normally distributed continuous variables. χ2 Tests were used for discrete variables. To evaluate the effect of the PRECON programme on RRI, a χ2 test was used. The log-rank test was used to compare the Kaplan–Meier curves of the subjects with an RRI in the PRECON group and the control group, analysing the difference between the training groups in the probability of an RRI at any time point. All analyses were performed following the ‘intention to treat’ principle. Differences were considered statistically significant at p<0.05. All analyses were performed using SPSS V.18.0 (SPSS Inc, Chicago).
Randomisation and baseline characteristics
Figure 1 shows the flow of participants through the stages of the GRONORUN 2 study. About 432 novice runners were randomly assigned to the PRECON group (n=211) or the control group (n=221). Baseline characteristics of all participants can be found in table 3.
Compliance with PRECON
In the 4 week PRECON programme 151 participants (71.6%) executed 10 or more training sessions. Thirty participants (14.2%) executed 7–9 training sessions and 14 participants (6.6%) trained 4–6 times. Sixteen participants (7.6%) of the PRECON group did not do any walking or hopping sessions at all.
Effect of the PRECON programme
The incidence of RRIs was 15.2% (26 of 171) in the PRECON group and 16.8% (32 of 191) in the control group. The difference in RRIs between the groups was not significant (χ2=0.161, df=1, p=0.69). Additional analyses (table 4) showed that the number of RRIs per 1000 h was 31.0 (95% CI 24 to 38) in the PRECON group and 30.0 (95% CI 24 to 37) in the control group. Survival curves (Kaplan–Meier) were made for both training groups (figure 2). The difference in mean survival time between groups was not significant (p=0.15).
Occurrence of running-related injuries
A total of 58 RRIs were recorded for both groups. Figure 3 illustrates the absolute number of RRIs per week in each training group. It shows that in the control group the most RRIs (n=18) were registered in the last 4 weeks of the 9 week running programme. The control group showed most RRIs in running week eight. In the PRECON group most injuries were seen in the second and fourth weeks of the 9-week running programme and in the sixth and eighth weeks when the 4-week PRECON programme was combined with the 9-week running programme. Descriptive information on RRIs is shown in table 5.
During the 9 week running programme participants of the control group completed more running minutes than participants in the PRECON group, respectively, 329.7±177.1 (67.3%) and 301.1±184.7 (61.4%). This difference in exposure time between the PRECON and the control groups was not significant. The exposure time until an RRI occurred was 149.5 (±123.2) min in the PRECON group and 206.0 (±156.5) for the control group (p=0.28). The non-injured runners in the PRECON and control group completed, respectively, 328.3 and 354.6 min of running in the 9-week programme. Compliance with the 9-week programme, with a total exposure of 490 min of running, was, respectively, 67.0% and 72.4% (n.s.) of total running volume for the PRECON and control group.
The results of the randomised controlled trial showed no effect of a 4-week PRECON programme on the incidence of RRIs. The incidence rate of RRIs was 15% in the PRECON group and 17% in the control group, and 31 RRIs per 1000 h of running in the PRECON and 30 RRIs per 1000 h in the control group.
Various reasons for the absence of an effect are conceivable. First, the intervention period may have been too short to gain a positive adaptation. Looking at the programme, it could be argued that this is not a PRECON programme by definition but a preloading programme and therefore the structural adaptations could longer to achieve an effect. Many studies on preconditioning used an intervention programme of 6 weeks24 ,26 ,27 or more.22 ,23 ,28 All studies found a positive effect on the incidence of sports injuries. There is also evidence however, for effects of short PRECON programmes. The study of Knapik et al25 showed that recruits who participated in a 3-week or 4-week PRECON programme were at a lower injury risk than other recruits with the same fitness level. One has to keep in mind that a preventive measure should be feasible and acceptable for participants.32 When extending the PRECON programme by 2–4 weeks there is a chance that the essential nature or appeal of running may be affected, thereby resulting in less participation or compliance.32
Second, participants in the PRECON group had to execute walking and hopping exercises on their own. Preconditioning or preseason programme exercises done under supervision for proper execution or in a group showed greater effects than non-supervised or home-based programmes.33 ,34 Non-supervised exercise programmes may also be less motivating and result in poorer compliance than a supervised and structured training programme followed among a peer group.34 ,35
Compared with other studies, the percentage of RRIs in the present study was relatively low (16%). In the literature the incidence of lower extremity running injuries ranges from 20.3% to 84.9%.2 ,5 ,7–9 ,11 ,12 ,17 ,36 Care should be taken when interpreting these figures, because additional analyses show that the number of RRIs per 1000 h running was 31 in the PRECON group and 30 in the control group. Incidences in the literature vary from 3 to 59 RRIs per 1000 h.2–6
The literature offers little information on the incidence of RRI among novice runners. The first GRONORUN study showed an injury incidence of 30 and 38 RRIs per 1000 h of running.4 That outcome is comparable with the incidence found in the present study. In the first GRONORUN study the risk of sustaining an RRI during a standard 8-week running programme was compared to a graded 13-week running programme. Another study that examined the risk of running injuries during a training programme was the Vancouver Sun Run.8 In a 13-week training protocol novice runners had to run in training sessions of 35–66 min three times a week. The injury incidence was 29.5 per 100 runners at risk. The number of RRIs per 1000 h was unknown. Length of the running programme and running frequency, that is, three times a week, were identical to those used in GRONORUN 1. The predominant sites of RRIs shown in the literature were the knee and lower leg.3 ,8 ,12 ,36 The results of the present study support these findings. The most frequently injured body parts were the knee (39%) and the lower leg (30%).
A limitation of this study is the low number of RRIs. Therefore, the study could be underpowered and outcomes of this study should therefore be interpreted cautiously. Another limitation could be the self-registration of RRIs. The RRI was not systematically diagnosed by an independent healthcare professional, and this may have biased the primary outcome measure. A third limitation was that there was no information on the intensity of running in the training programme. It is possible that a high percentage of the injured runners trained at too great of an intensity or duration for their level of fitness. Participants were instructed to run at a comfortable pace at which they could converse without breathlessness but this was not objectively measured. The 9-week running programme was based on minutes of running and not on distance. Training pace could have resulted in a different weekly training volume. A fourth limitation was the high number of participants that did not start running the 9-week running programme after inclusion. This may have affected study outcomes. A fifth limitation could be the self-reported adherence to the intervention programme used to quantify compliance. Although the compliance looked high, this method of quantifying adherence carries a potential risk of bias.
The risk of an RRI will always be present among novice, recreational and competitive runners. A runner with an overuse RRI must have exceeded the stress-frequency curve in terms of running distance or intensity in a way that there is too little time for recovery or positive adaptation of the musculoskeletal system. Running causes a physiological or pathological adaptation to this mechanical loading, resulting in respectively a training effect or overuse injury. Besides the training, there has to be an underlying intrinsic, anatomical or biomechanical factor that will influence the stress frequency curve in a positive or negative direction. Preconditioning programmes should consider the possibility for variation and progression in the prescribed exercises, which will avoid ceiling effects, enhance motivation among trainers and athletes and favour compliance.35 The duration of a PRECON programme should be ideal: not too short, for a lack of training effect and adaptation, and not too long, to prevent boredom and dropout. Compliance should be carefully monitored because it is an important factor for the effect of a preventive measure. Exposure data should measure pace, speed, distance and intensity. With new portable running measurements systems with Global Positioning System sensors this should be possible even in a large study cohort. And last but not least, the effectiveness of an injury prevention programme depends on its content and on the success of its relatively permanent acceptance and implementation within the sports community among athletes, trainers, coaches and sport organisations.
In conclusion, this prospective GRONORUN 2 study demonstrated that a 4-week non-supervised PRECON programme with walking and hopping exercises had no influence on the incidence of RRIs in novice runners preparing for a 4-mile recreational running event. This was, to our knowledge, the first PRECON study in running. Attention should be paid to type of exercise, duration, progression and programme variation in order to promote compliance and efficacy. Exposure in running should be monitored carefully in terms of speed, intensity and duration. Even though it may be comparable to the quest for the Holy Grail further studies on modifiable risk factors and prevention of running injuries need to be performed to better advise runners in the future.
This is the first study among runners that evaluates the effect of preconditioning in preventing running-related injuries (RRIs).
The 4-week preconditioning programme did not prevent RRIs in novice runners.
Contributors SWB conceived of the idea, obtained funding for the study and developed the intervention. SWB and IB developed the design of this trial and recruited participants. SWB, IB and BB were the study investigators and wrote the article, SZ was responsible for data acquisition. IB was coapplicant of the grant. All authors read and approved the final manuscript.
Funding This study was funded by the Netherlands Organisation for Health Research an Development (ZonMW), grant number 75020009.
Competing interests None.
Patient consent Obtained.
Provenance and peer review Not commissioned; externally peer reviewed.
▸ References to this paper are available online at http://bjsm.bmjgroup.com