Wherever possible RunningPhysio tries to be evidence based but in many cases there is a lack of high quality research. Extensive advice exists on injury prevention in runners and yet the research underpinning that advice is very limited, so limited in fact that one recent study described it as “skimpy”! So we decided we'd examine this “skimpy research”.
In February 2012 The International Journal of Sports Physical Therapy published an extensive study that examined training errors and running related injury. The study, Nielsen et al. (2012), performed a systematic review of the research in this field. Out of 63 articles that were found to be potentially relevant, 32 met their inclusion criteria and were included in the study. In total, these 32 studies involved 24,066 participants (runners of varying experience).
Nielsen et al. (2012) explored the relationship between trainining volume, duration, intensity and frequency and running related injury (RRI). We'll examine their findings.
Training volume and duration
Training volume in running is essentially how much you run (not taking into account speed, intensity etc). As runners we usually think of it as miles per week and Neilsen et al. used this as their main measure of training volume. When measuring injury rate they used both risk of injury and injury incidence per 1000 hours of running. This makes their conclusions a little confusing. As I understand it they found an increase in risk of injury with an increase in mileage. However they also reported a reduction in injury incidence per 1000 hours of running in runners with greater mileage. So, because you run more you may be at higher risk of injury, but per hour you run your injury risk is actually lower. They concluded,
“There is some evidence suggesting weekly mileages to be associated with injury. However, the relative injury threshold becomes greater in runners with higher weekly mileage.”
This is of no great surprise to me! High mileage runners I've worked with are experienced, and know their limits. Running 60 miles per week compared to 20 may not place you at a significantly higher risk of injury if that is what your body is used to.
Increase in mileage is perhaps a more relevant training variable to study. Neilsen et al. (2012) explore this but there is surprisingly little research on it – they included just 1 study on increasing mileage in their review. The study, by Buist et al. (2008) is the only one I'm aware of that has examined the fabled “10% rule”.
Buist et al. compared a graded training programme where weekly running duration was increased by 10.5%, with a “standard” programme with increases of 23.7%. The study involved 532 novice runners. They trained for a 4 mile event, with the standard group training over 8 weeks, and the graded training taking 13 weeks. There was no significant difference in injury rates between the groups. The standard group had an injury rate of 20.3% while the graded programme was 20.8%.
While this may sound like it suggests there's no advantage to a graded training programme it is worth remembering that previously reported injury rates in novice runners are 29 to 58% so both groups scored low. The standard group can't really be desribed as “standard” in my opinion – taking 8 weeks to reach the distance of 4 miles could easily be seen as a graded increase in distance. What they have really compared is 2 graded training programmes and both have scored lower injury rates than you might expect to see normally.
My biggest concern with this study though is the target distance of 4 miles. Research by Walter et al. (1989) found a decreased risk of injury in runners whose longest run each week was below 5 miles and I feel risk of injury for a relatively low distance like this is likely to be small. Also, although the difference in percentage increase may appear reasonable, in reality how this affected the training appeared minimal – on average the standard group completed 59 minutes of training per week, while the graded group completed 52. Did they really expect 7 minutes to make a big difference? When you consider this time was spread over 3 training sessions per week it makes you question the design of this study.
The 10% rule will vary greatly depending on your starting point too. For those starting with a weekly mileage of 2 miles their increase in distance will be very gradual, they will take 4-5 weeks to progress to 3 miles. For runners managing 30 miles per week they'll be progressing to 40 miles in just 3-4 weeks. If you started to use a 24% increase (used in the “standard” group above) when running 30 miles per week you'd progress to 60 miles in just 3-4 weeks!
All Buist et al. can really conclude is that you may not need to stick to the 10% rule when doing lower distances. Further research is needed to examine the effects of a graded programme over greater distances.
The results from the research reviewed by Nielsen et al. were mixed for the role of intensity of training. Two studies found a higher injury rate in faster runners, and ITBS and Achilles tendinopathy were both associated with running at a faster pace. However 8 other studies found no significant relationship between average training pace and likelihood of injury leading Nielsen et al. to conclude,
“The literature showed conflicting results with regard to training intensity and development of injuries…more studies have to be conducted to ascertain if there is a relationship between training intensity and development of injury”
Nielsen et al. reported a “U-shaped” curve which revealed higher injury rates at training once per week and 6-7 times per week. It would appear the optimum training frequency may be 2-5 times per week, however there was a great deal of variety in the literature leading Nielsen et al. to observe,
“It must be concluded that it is not possible to determine the specific role of running frequency with regard to injury”
Additional findings in research
Bredeweg et al. (2012) compared two groups of novice runners who both completed a 9 week running programme. One group did a 4 week preconditioning programme of walking and hopping and the other acted as a control. There were 432 runners in total. They found no significant difference between the 2 groups with the preconditioning group having an injury rate of 15.2% and the control group 16.8%. The study has similar methodological issues to Buist et al. (2008) – both groups completed a running programme involving a gradual increase in mileage to a relatively low distance and again injury rates were relatively low.
You've battled through this article and I wish I could reward your efforts with a grandiose conclusion to make it all worth while. Sadly I can't. All we can say is that once again the research is inconclusive. Regular followers of RunningPhysio will know of the ongoing debate we have with those staunch supporters of research who insist we must be evidence based. Surely this shows us just how unhelpful research can be in reality – over 30 studies, involving 24,000 runners and no firm conclusions on injury prevention! No wonder Verhangen (2012) described it as “skimpy published research” and went on to conclude,
“Specifically for novice runners knowledge on the prevention of running injuries is practically non-existent“.
Nielsen et al. isn't the first review of its kind in this field – a Cochrane Review in 2001 reached a very similar outcome and was updated in 2011 with equally negative conclusions; Yeung, Yeung and Gillepsie (2011) completed a review of 25 studies, including over 30,000 particpants and concluded,
“Overall, the evidence base for the effectiveness of interventions to reduce soft-tissue injury after intensive running is very weak.”
I acknowledge the vital role research plays in injury prevention and physiotherapy as a whole, but perhaps it's time for a change in how this research is carried out. More attention should be paid to changes in training charactisitcs rather than the characteristics themselves. Representatives from the running community need to be involved with the process to keep this research relevant and realistic. Is using a 13 week training programme to reach 4 miles realistic, when you consider many marathon training programmes are 16 weeks? Discussing this topic with runners revealed many started at around 2 miles and progressed to 4 within a few weeks or a couple of months. Only a select few took over 3 months to run 4 miles.
Bredeweg et al. (2012) commented in their research,
“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.”
Direct involvement of the running community in injury prevention research would surely aid in creating interventions that are accepted and easily implemented.
In the absence of firm guidance from the literature we follow an approach based on experience and clinical reasoning and make the following recommendations;
Novice runners should be especially cautious with increasing volume or intensity of training.
Increase in weekly mileage should be done gradually. The higher the weekly mileage the more caution needs to be applied in increasing this distance. Running expert Hal Higdon talks about runners having a 'breaking point' – a weekly mileage above which they start to develop injuries. For every runner this is different but with experience you can find your breaking point and aim to work below it. A gradual increase in mileage helps avoid crossing this point and picking up an injury.
Changes in intensity of training should be added in isolation, rather than combined with increase in distance. Be cautious when adding interval training or hill work and use each training session for its specific goal (i.e.long slow runs at an appropriately slow pace).
Be aware of signs of injury – look out for persistent or severe pain, swelling, restricted movement or sensations of giving way.
Use rest sensibly – don't be afraid to rest or replace running with cross training when your body needs it.
Seek help – the right GP, Physio or health care professional can make a real difference!