The runner, whether starting a new running program, returning from an injury or training for a new race goal, often questions how and when to increase running mileage. While runners are often looking to run faster and farther, progressing mileage too quickly harkens fear of injury or over-training.
Training errors are a leading cause of preventable injuries as many runners follow the paradigm of ‘too much, too soon, too fast and too frequent to gain the competitive edge. The 10% rule, a longstanding, familiar guide for the runner, states that one should not increase their weekly run mileage by more than 10% in an effort to minimize over-training induced injury. While the origin of this declaration is lost to history, and is most likely a construct of how we tend to lump numbers in blocks of ten (so that things make better sense), its conceptual importance is not diminished. However, validity of this rule is questioned as related to injury prevention while allowing optimal progression of aerobic running fitness.
Does the 10% rule help or hamper the runner?
Researchers followed 873 new runners for 1 year in which 202 runners (22%) had a running-related injury. Injuries were compared based on each participant’s weekly increase in run mileage as the runners were designated in three training groups:
- Less than 10% weekly mileage increase in the 2 weeks prior to injury,
- 10% to 30% weekly mileage increase in the 2 weeks prior to injury, and
- more than 30% weekly mileage increase in the 2 weeks prior to injury
- Novice runners who progressed their weekly running distance greater than 30% were more vulnerable to distance-related injuries, such as patellofemoral pain, iliotibial band syndrome, medial tibial stress syndrome, patellar tendinopathy, gluteus medius injury, greater trochanteric bursitis, and injury to the tensor fascia latae, than runners who progressed their running distance less than 10%
- The 10% rule relationship was not present for other injury types like traumatic injuries or pace-related injuries such as Achilles tendinopathy, plantar fasciitis, tibial stress fracture, hamstring injuries, iliopsoas injuries, and calf injuries.
The researchers identify that the biomechanical rationale for injury as related to the increase in weekly run distance is unknown. However, it is plausible that running longer distances than usual potentially forces the runner to decrease running speed, especially with fatigue. Studies show that as running speed decreases, ground contact time increases. Since ground reaction and joint loading forces are increased during slow-speed compared to faster running , the increased loading forces offers a greater potential for injury.
In contrast, another biomechanical rationale suggests a sudden increase in running speed to be linked with the aforementioned injuries like Achilles tendinopathy, plantar fasciitis, tibial stress fracture, hamstring injuries, hip flexor and calf injuries. This may be the reason for the difference in the results across distance and pace-related injuries.
RUNNING INJURIES: Increase in weekly run distance by more than 30% over a 2-week period may increase risk for developing patellofemoral pain, IT band syndrome, medial tibial stress syndrome, patellar tendinopathy, trochanteric bursitis, and gluteus medius or tensor fascia latae injury
However, in a real world application of this research finding, one must use caution when designing or progressing a running program.
These studies did not take into account volumes and potential changes in workout intensity during the weeks that mileage increased. Increased intensity coupled with high mileage progression could potentially increase injury potential.
Additionally, one must consider the volume of miles per week the real world runner potentially engaged in weeks prior to the increase. Previous high mileage percent progressions followed by continued high mileage increase could also increase injury potential
One has to consider how mileage is progressed within the ranges presented in these studies. The research outcomes could lead the runner to believe that keeping the increase in mileage to less than 30% would keep the injury rate low, no matter how the runner scheduled their running plan. An assumption such as this can be quite risky for the runner.
For example, the injury rate may be low when increasing the weekly distance by, for example, 10% on week 1, 12% on week 2 and 15% on week 3 (2 and 3% respectively, for each week’s progression). But, the injury rate may potentially be higher when progressing in larger bunches such as from 15% to 25% and finally to 30% over a 3 week period (5%, for each week’s progression, or from 18% to 22% to 24% over a 3 week period (4%, for each week’s progression) – even though the progression did not exceed 30%. In these examples, while the volume increases per week were relatively small (ranging from 2 to 5%), the overall volumes of mileage increase were higher in the 2nd and 3rd examples (15 to 30%). The research has yet to identify how the experienced or inexperienced runner may benefit or become injured when mileage is progressed with successive larger volumes.
The lowest injury rates are found in runners who increase their weekly mileage by less than 10% up to 22% over 2 weeks. Other running injuries may be linked to running pace, increasing running speed, sprint training, or other training errors.
Research does not identify how the progression of mileage, over successive weeks, at higher percentages (i.e. 15 … 20 … 22%) may influence injury rates, especially for the new runner or the experienced runner who may be under a higher level of training stress due to previous high mileage volumes, frequency of high intensity workouts, etc., therefore, it is suggested that the runner err on conservative progressions to offer optimal aerobic fitness progression while inhibiting injury.
Runner A: Low mileage runner .. low mileage progression
Week 1 = 15 miles per week
Week 2 = 16.5 miles per week (10% mileage increase)
Week 3 = 19 miles per week (15% mileage increase)
Week 4 – recovery volume week = 14 miles per week
Runner B: Medium mileage runner … high mileage progression
Week 1 = 28 miles per week
Week 2 = 36 miles per week ( 18% mileage progression)
Week 3 = 44 miles per week ( 22% mileage progression)
Week 4 – recovery volume week = 33 miles per week
Runner C: High mileage runner … medium mileage progression
Week 1 = 60 miles per week
Week 2 = 69 miles per week (15% mileage progression)
Week 3 = 81 miles per week ( 18% mileage progression)
Week 4 – recovery volume week = 60 miles per week