Fitness: Putting 10 per cent rule to the test
Much of those injuries are related to overuse or, in the case of many runners, too steep an incline in mileage over too short a period of time. Doing too much too soon is a common training error made by even the most seasoned runners. Yet little is known about exactly how much is too much. The 10 per cent rule is a commonly quoted guideline, suggesting any sudden increase in mileage over 10 per cent is a precursor to injury. Normally, increases in training volume are calculated from week to week, but there's been some suggestion it takes less than a week for an overuse injury to settle in, a theory a Danish team of researchers put to the test.
'In running, emerging evidence from our research shows that few runners report symptoms before an injury occurs,' the researchers said. 'This suggests that runners may be more vulnerable when increasing distance too rapidly within a single session.'
The researchers recruited 5,205 runners (4,053 male, 1,152 female) from North America and Europe who were a median age of 45.8 years with an average of 9.5 years of running experience. Using data from their Garmin watches to determine training load, the researchers calculated any increase in distance by comparing the length of a single training session to the longest run in the previous 30 days (15k/10k=50% increase) over an 18-month period or about 80 running sessions. Increases in training volume of the total cohort were grouped into four categories: regression (running less than the longest run — 10 per cent increase), a small spike (11-30 per cent), moderate spike (31-100 per cent) and a large spike (greater than 100 per cent). Injuries were self-reported.
Of the 5,205 runners, 35 per cent (1,820) reported an injury of which 72 per cent (1,311) were considered overuse. Small spikes in distance increased the risk of injury by 64 per cent. Moderate spikes resulted in a 52 per cent bump in risk and large spikes in training volume increased the risk of injury by 128 per cent. Injury rates were not affected when using a weekly (versus a single session) ratio to calculate spikes in running volume.
'These findings suggest a paradigm shift in understanding running-related injuries, indicating that most injuries occur due to an excessive training load in a single session, rather than gradual increases over time,' the researchers said.
That shift in understanding relates to the current theory that broadly states weekly increases in volume of 10 per cent or less will keep most runners safe from injury. But it looks like increasing the distance of a single run is the real culprit behind many overuse injuries. And even a modest 10 per cent increase isn't without risk.
'Although not statistically significant, a progression between one per cent and 10 per cent translated into an increased rate of 19 per cent, compared with regression or progression up to one per cent,' the researchers said.
This discovery is especially important to novice runners, runners who are gradually increasing their training volume in preparation for a longer run (10k, half-marathon and marathon distances) and runners recovering from an extended time away from running. It's common during weekly progressions to increase the distance of a single long run by 10 per cent or more and keep the rest of the weekly runs similar in distance. But it looks like it would be more prudent to either spread those weekly changes in running volume over several runs or keep any increases to a single run to less than 10 per cent, especially if you're prone to injury or or coming back from an injury.
That means revising most training calendars designed to prepare runners for a marathon or half-marathon. Instead of taking 16-20 weeks for novices and 12-16 weeks for more experienced runners, plan on giving your body even more time to adapt to longer runs. And since most on-line training programs plan their long run progression on a week-to-week basis, it means doing the math and changing weekly mileage goals to ensure no single run is more than 10 per cent longer than the previous run.
'Notably, a spike of 10 per cent in single-session running distance significantly increased the rate of overuse running-related injuries, with the risk sharply rising when the distance more than doubled,' the researchers said.
Keep in mind this study only focused on injury as it's related to training volume. Other training errors like not enough recovery or rest, changes in terrain, poor technique and inconsistent training can contribute to injury. So, too, can inherent biomechanical issues like a faulty foot strike, a mismatch between runner and footwear and muscle imbalances. With injuries so prevalent among runners, understanding how to better manage increases in training volume is an opportunity to stay healthier longer.
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'In running, emerging evidence from our research shows that few runners report symptoms before an injury occurs,' the researchers said. 'This suggests that runners may be more vulnerable when increasing distance too rapidly within a single session.' The researchers recruited 5,205 runners (4,053 male, 1,152 female) from North America and Europe who were a median age of 45.8 years with an average of 9.5 years of running experience. Using data from their Garmin watches to determine training load, the researchers calculated any increase in distance by comparing the length of a single training session to the longest run in the previous 30 days (15k/10k=50% increase) over an 18-month period or about 80 running sessions. Increases in training volume of the total cohort were grouped into four categories: regression (running less than the longest run — 10 per cent increase), a small spike (11-30 per cent), moderate spike (31-100 per cent) and a large spike (greater than 100 per cent). 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So, too, can inherent biomechanical issues like a faulty foot strike, a mismatch between runner and footwear and muscle imbalances. With injuries so prevalent among runners, understanding how to better manage increases in training volume is an opportunity to stay healthier longer.
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