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Running is one of the fastest-growing sports activities worldwide. In the Netherlands, with a population 17 million, about 1.4 million individuals engage in this activity regularly—either as part of a club or as an individual. Reasons for the contemporary public interest in running probably include a desire for weight reduction or a healthy lifestyle in general, combined with the low entry level, quick health effects and social elements. This is encouraging from a public health standpoint.
On the other hand, the most recent Dutch sports injury data reveal that 420 000 of our 3.5 million annual sports injuries are running related. This represents 5.1 injuries per 1000 h of running.1 Novice runners have a much greater risk of injury than do those who have been running for some time.2 Injuries work against the potential public health gain of running. Prevention of running injuries in novice runners will promote running consistency. In combination with the current running ‘hype’ and the positive health effects achieved through running, successful injury prevention could contribute substantially to both short-term and long-term public health.
Skimpy published evidence
There are very few (randomised) controlled trials on the effectiveness of preventive interventions for running injuries. A 2011 Cochrane review on prevention of running injuries revealed a total of 25 intervention studies on the prevention of soft-tissue running injury.3 While this presents a meagre number, it is even more striking that only three studies were situated in a general population of runners, of which only one specifically studied novice runners.4 No conclusive preventive effect was found for (1) warming-up, cool down and stretching exercises; (2) use of external devices (eg, shock absorbing insoles); and (3) modification of training schedule. The authors called for more well-designed randomised-controlled trials (RCTs) in both recreational and competitive runners. Note that novice and more experienced runners appear to be two different breeds of athlete. Risk of injury and type of injury differ greatly between both types of runners.2 In this Editorial we highlight four issues that need to be addressed in a study that will help clinicians and runners prevent injuries.
Sample sizes must be appropriate
The prime issue future studies on running injury prevention need to address is sample size. As an example, we could calculate the sample size required for a preventive study using a β of 0.80 and a α of 0.05. For novice runners the literature reports injury rates between 29% and 58%. A recent Dutch 8-week prospective study revealed an injury rate of 29.5% in a group of 629 novice runners.5 Let us consider this follow-up period of 8 weeks and take an injury rate of 30% for running injury incidence. Because no effective preventive interventions are described in the literature we have no benchmark of an achievable effect. On the basis of our expertise we find a 25% reduction in running injury, both realistic and clinically relevant. From these numbers a total of 1080 novice runners are required (2×540). Assuming an attrition rate of 15% (not related to a running related injury) during the intervention period, a sample of 1242 (2×621) novice runners is required at baseline. This is more than twice the numbers in the only available study on novice runners to date (523 participants).4 Importantly, there was no trend in reduced running injury risk in that study by Buist. Therefore, a larger sample would not have altered conclusions. In general, longer follow-up periods lead to higher injury rates, and thus decrease the required sample size. However, in an individual sport as running longer follow-ups are a logistical challenge.
Overloading versus ill-loading
Either reducing the load or increasing the loading capacity might reduce running injury. However, we must take into account that the specific loads leading up to running injuries are biomechanically different and caused by local overloading of the musculoskeletal structures. Although it remains speculative, each runner likely has an individual set of weak links that are predisposed to injury (eg, a weak spot in the tibia leading to tibial stress fracture before other running injuries). If load is consistent throughout the system this should lead to one injury occurring much more frequently than others (eg, where load is maximal). Then why do we see such a spectrum of different injuries between runners and why do not we find bilateral problems within runners? It may be that rather than running specifically overloading the entire system (and causing the weak link to break first), running injuries may be caused by overloading of specific soft-tissue structures? In other words, is the load capacity reduced or is the load increased in certain soft tissue structures. There is current—shallow and disputable—evidence that supports both options. More research here is required as preventive measures need to grip upon such aetiological factors.
Reduced loading capacity—adiposity and risk for soft tissue injury
Gaida and colleagues6 have reported that elevated adiposity is associated with tendon injury. Elevated adiposity is associated with high cytokine levels and a number of mechanisms exist whereby elevated cytokine levels may either directly or indirectly affect tendon structure.7 Thus, decreasing the capacity of tissue to absorb load. Many novice runners are overweight—it is one motivation for beginning running. If there is a link between adiposity and soft tissue injury, this might well be an important factor contributing to running injury risk in this specific group. Moreover, this would also prove to be a factor of particular interest for running injury prevention.
Ill-loading—running kinematics and risk for soft tissue injury
Over the past few years, several studies have established a relationship between faulty running mechanics and overuse injuries such as tibial stress fractures and patellofemoral pain syndrome. A review of running injury risk factors noted that weakness in the core muscles may translate into a higher risk of running-related injuries.8 In novice runners, we recently examined kinematic changes that occurred during running-induced fatigue and how this varied with core stability. We found that novice runners altered their trunk flexion and extension, indicating an overall increase in trunk-flexed posture during fatigued running. Changes in hip extension, ankle pronation and ankle supination also occurred. Thus, running mechanics do change with fatigue in novice runners, putting additional or altered mechanical stress on the soft tissue structures of the lower extremity.
Although running is a popular activity for health benefit, the risk for running injury should not be neglected. Specifically for novice runners knowledge on the prevention of running injuries is practically non-existent. In a pursuit to attain high-quality evidence on effective preventive efforts, we must take into account that novice runners have a specific injury risk and that preventive efforts should be tailored to this group. The health status at running onset and mechanical alterations during running may provide potential hooks for future effective programmes.
Competing interest None.
Provenance and peer review Commissioned; internally peer reviewed.
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