Introduction:
Running related injuries are commonly seen in orthopedic and sports clinical practice. The incidence of injury reported in literature is variable and ranges from 19-79%.(1) This wide range of reporting is partly due to the heterogeneity of studies and differences in the operational definition of a “running related injury” (time loss vs. non-time loss, etc.).
Running related injuries are multifactorial in nature and therapists must identify which factors are at play when evaluating an injury. Careful attention should be directed at modifiable risk factors including training variables (frequency, intensity, and duration), training modes (running, cross training, etc.), nutrition, and sleep, making referrals as needed.
The purpose of this literature review will be to establish guidelines to assist clinicians in transitioning a patient back into mid- to long-distance running following an injury or to assist them in managing volume to reduce injury risk.
Etiology of Running Related Injuries (RRI):
Anecdotally running related injuries are most commonly related to training error and this is supported by Nielson et al.(2) and others.
Studies have found that both a very low frequency (2 or fewer days per week), and a very high frequency (5 or more days per week) of running are associated with a higher risk of running related injury.(1)
Ramskov et al.(3) found that a similar injury rate occurred between groups of runners that increase running volume (duration at a lower percentage of VO2max), and those that increase running volume at a higher intensity (duration at a higher percentage of VO2max) following a period of identical pre-conditioning. Their findings suggest that running intensity alone is not a risk factor for injury and that there is an interplay between training variables that contributes to running related injuries.
It may be interpreted that there is an optimal training dosage for a given individual that reduces injury risk to a reasonable level. The interplay of frequency, intensity, and duration must be considered when determining the optimal dosage, and progressions must be individualized to ensure a lower injury/re-injury risk.
Strategies for Progressions in Volume:
“10% Rule”:
There is a commonly described “10% rule” of increasing running volume. Runners should increase total volume each week by no more than 10% of the prior week. While this is certainly protective and limits the chances of sustaining a running related injury in the short-term, some have questioned that the 10% rule may be too conservative and increase the time to appropriately prepare for a given event.(2) This would be associated with more time spent running, thus increasing the chance of injury based on incidence rates.
Challenging the “10% Rule”:
Nielsen et al.(2) conducted a 10-week prospective observational study investigating the relationship between progressions in running volume and injury.
Following the 10-weeks participants were stratified into “injured” and “healthy” groups. While not statistically significant, they found that injured participants on average increased volume by 31.6 +/- 3.1% compared to only 22.1 +/- 2.1% by healthy individuals.
Practically, this study demonstrates that weekly training increases in distance of 30% or more may be associated with increased risk of injury. It also suggests that progressions in volume of 20-25% per week are reasonable over a shorter period of time for healthy, novice runners.
Acute to Chronic Workload Ratio:
Hulin et al.(4) investigated the relationship between “Acute to Chronic Workload Ratio” and injury risk in elite professional rugby athletes. Specifically, they researched injury risk based on acute to chronic workload ratio in elite rugby professionals when measuring running volume by GPS monitoring. While rugby does occur at a reasonably higher intensity compared to distance running, there may still be some practical applications for this population based on their research.
They defined chronic workload as the average mileage per week of the prior month’s training. The ratio is found by dividing the current week’s mileage by the chronic mileage. They were able to demonstrate differences in risk of injury in both the current and subsequent weeks based on the acute to chronic ratio (see below how to calculate this value).
Key findings from this study include:
- A higher chronic workload is associated with an increased resistance to injury with moderately low to moderately high A:R ratio (0.85 to 1.35).
- Conversely, a high chronic workload is associated with a decreased resistance to injury with a very high A:R ratio (1.5+)
- A higher A:R ratio is associated with increased risk of injury.
- A higher 2- week average A:R ratio is strongly associated with injury risk.
This study highlights the importance of establishing and maintaining a chronic workload to increase resistance to injury. This is important in terms of managing a runner presenting to the clinic for evaluation. In the absence of red flag symptoms or a more acute injury requiring careful management, I would recommend finding a way for them to modify rather than abstain from their training. This may result in increased athlete buy-in, a greater perceived self-efficacy, and an ability to maintain some level of training volume, shortening their return to their prior level of activity.
Additionally, this study highlights the importance of varying weekly training volume (and perhaps intensity) to enhance performance, maximize recovery, and maintain resistance to injury.
Practical Applications:
The figure below details a clinical decision-making tool based on the above strategies to assist clinicians in making recommendations to patients. Important considerations for this tool include the patient’s training age, length of time off due to their injury, and whether they are a competitive versus a recreational runner.
When making recommendations to patients, it is helpful to stratify them into one of two groups:
1) novice, or those returning to running following a prolonged time off running due to injury or
2) those runners who are well trained (increased training age) or those running through a nagging injury with an upcoming event or goal they are trying to achieve.
Secondly, clinicians must decide whether the athlete has established a sufficient chronic workload prior to determining appropriate progressions in training volume. See the below figure detailing different levels of chronic workload. These levels are largely based on arbitrary volumes however they do provide a starting point for clinicians.
| Chronic Workloads | |
| Low: | < 6 mi/week |
| Moderate: | 6-12 mi/week |
| High: | 12-24 mi/week |
| Very High: | 25+ mi/week |
Once a patient has established a sufficient chronic workload it is possible to make more informed recommendations surrounding their progressions in training volume. When consulting with a patient it is helpful to know the answers to the following questions to increase the chance of successful outcomes:
- How often would you like to run?
- In the past how many miles per week did you run on average?
- Do you have a specific goal or event you are training for?
- In the past, have you varied your weekly mileage or utilized “deload” weeks?
- Have you varied pace (intensity) in your training?
- Do you complete any other forms of exercises aside from your running?
- Do you keep a training log? And do you review it?
Conclusion:
When considering progressions in running volume, it is important that a chronic workload has been established due to its protective effect when increasing volume. However, it is also important that acute increases in volume are matched to the established chronic workload to avoid significant increases in injury risk.
For novice, recreational, or those runners returning to training following a lengthy time off, standard linear increases in training volume of 10-23% more consistent with the “10% rule” are appropriate and likely safe.
For those runners who are competitive, training for an event or goal mileage, or those looking to fine-tune their training plans and willing to learn, it is appropriate to review acute to chronic workload ratios and their applicability to training programs.
Citations:
[1] van Gent R, Siem D, van Middelkoop M, van Os A, Bierma-Zeinstra S, et al. (2007) Incidence and de- terminants of lower extremity running injuries in long distance runners: A systematic review. Br J Sports Med 41: 469–480. PMID: 17473005
[2] Nielsen, R. O., Cederholm, P., Buist, I., Sørensen, H., Lind, M., & Rasmussen, S. (2013). Can GPS Be Used to Detect Deleterious Progression in Training Volume Among Runners? Journal of Strength and Conditioning Research, 27(6), 1471–1478. doi: 10.1519/jsc.0b013e3182711e3c
[3] Ramskov, D., Rasmussen, S., Sørensen, H., Parner, E. T., Lind, M., & Nielsen, R. O. (2018). Run Clever – No difference in risk of injury when comparing progression in running volume and running intensity in recreational runners: A randomised trial. BMJ Open Sport & Exercise Medicine, 4(1). doi: 10.1136/bmjsem-2017-000333
[4] Hulin, B. T., Gabbett, T. J., Lawson, D. W., Caputi, P., & Sampson, J. A. (2015). The acute:chronic workload ratio predicts injury: high chronic workload may decrease injury risk in elite rugby league players. British Journal of Sports Medicine, 50(4), 231–236. doi: 10.1136/bjsports-2015-094817
