Does the amount of running hours and frequency increase your chances of a running injury? This study suggests not.
A step towards understanding the mechanisms of running-related injuries, by Malisoux, Nielsen, Urhausen, and Theisen, in Journal of Science and Medicine in Sport (2015)
All physical activity involves a certain risk of injury, whether acute (traumatic) or chronic (overuse). For elite amateur and professional athletes, these risks are accepted in return for the ultimate reward that comes from successful participation at the highest levels. On the other hand, for non-elite amateur athletes and individuals who make use of participative sport for the purposes of exercise, injury risk (as well as enjoyment) should be an important factor in deciding which type of sport to take part in. Some of the most popular amateur exercise pastimes are long- distance running, cycling and triathlon. However, the injury risk associated with long-distance running is high. Injury risk in sports is typically assessed by reference to prevalence, incidence or rate. Injury rates provide the best metric for understanding injury risk, as they correct for the number of hours typically spent in performing the activity. Injury rates in long-distance running reported in the literature range from 2.5 – 12.1 injuries per 1,000 hours training. Injury rates in triathlon are typically around half as high, from 1.4 – 5.5 injuries per 1,000 hours training, which may imply that not focusing solely on one activity is less injurious from an overuse perspective, or it may imply that swimming and cycling are fundamentally less damaging than running. The injury incidence in long distance running is also very high, with between 27 – 79% of recreational and competitive runners sustaining overuse injuries over the course of a single year. Injury during long-distance running is thought to arise from repetitive stress, which causes cumulative micro-trauma, leading to overuse injury. Consequently, a great deal of time and effort has been devoted to finding different strategies that might reduce loading and prevent overload. Proposals for helpful strategies include: varying the type of loading by performing a greater amount of cross-training rather than running, switching from rear-foot to mid- foot or forefoot striking patterns in order to reduce the ground impact forces, varying shoe types in order to alter the loading patterns, and strengthening lower body muscles in order to improve their ability to perform a shock-absorbing role during ground contact.
OBJECTIVE: To investigate the influence of running time (in hours per week) and frequency (number of sessions per week) on the incidence of running injury in recreational runners. The definition of running injury was taken as “any physical pain located at the lower limbs or lower back region, sustained during or as a result of running practice and impeding planned running activity for >1 day”.
POPULATION: 517 recreational runners (running >1 time per week), aged 42.2 ± 9.9 years.
Running time, frequency, distance and speed
The researchers found that their subjects ran for an average of 2.1 ± 1.1 sessions per week for a total running time of 2.3 ± 1.6 hours per week. The mean running distance was 22.1 ± 16.2 km per week and the average running speed was 9.6 ± 1.6km/h.
Running injury rate
The researchers found that 167 of the 517 subjects (32.3%) sustained a running injury during the period in review. Using the running time data provided, this corresponded to 6.7 injuries per 1,000 hours of running. Of these injuries, 32.9% were recurrent and the remainder were novel. Unsurprisingly, the most common injury locations were the lower leg (22.7%), knee (22.2%) and thigh (20.9%).
Factors influencing injury risk
Counterintuitively, the researchers found that weekly time <2h was associated with a 3.3 times greater risk of running injury than >2h and that <2 sessions per week was associated with a 2.4 times greater risk of running injury than >2 times per week.
What did the researchers conclude?
The researchers concluded that the exact relationships between weekly running time and running injury and between session frequency and running injury are very unclear. The data in the current study suggest the presence of counterintuitive relationships, such that fewer running sessions and short running times are associated with greater risk of injury. Such results may be a feature of experience and/or training consistency.
The study was limited in that there was no measure of running consistency assessed in the model.