Kevin,
You are correct, there is no good way to compare an 8 week vs. 13 group running program. This is another poorly conceived and executed study. This one though conforms to criteria which gives it the highest ranking within Evidence Based Medicine standards, an inexplicable paradox.
The authors were apparently stunned to learn that if you ran for more than a 50% longer time period than those you were being measured against, you might risk more injury.
The details:
Both studies had a gradual build up, not a random number of minutes run per week. The entire program was not spelled out but included both a 5 minute walking warm up, 3 days per week of running, and some walking added in. The 10% increase group ran for 13 weeks, while the standard group ran only for 8 weeks. The culmination was a 4 mile race/run.
There were differences in the groups. The Gradual Increase group had a small but significantly higher BMI. An attenmpt to lessen the risk of BMI in the different groups was attempted using
"Cox proportional hazards regression analysis". The standard group had significantly more drop outs that were not included in the study. No data was recorded or available for them. The number of failures to be included was literally more than twice as high in the "standard group": 11.9% vs. 5.3 or 32:14. If those drop outs were included as "injured" the results would have been radically different. The runners in the standard group included a higher number of experienced runners 55% vs. 50% in addition to being lighter, they were also more likely to be fit.
Another attempt to make up for the differences in the number of weeks run was the use of "survival curves" or Kaplan-Meier Curves. The survival time of those in the gradual training group was 212 vs. 167 in the standard group. This was not deemed statistially significant.
When the authors discovered that their "hypothesis" was not panning out they did further evaluation and noted the obvious. Those in the gradual increase running in running group had a lower RRI/1000 hours of running. It did not reach statistical significance with these study numbers however although it seemed to be about one injury away from statistical significance. The authors noted that their study was much too small to measure this very important and even superior parameter.
During the 4 weeks in which the gradual program continued to run and the standard did not, there were 13 injuries in the gradual group. During the initial 8 weeks of each groups training there were 48 Injuries in the Standard group vs. 41 in the Gradual.
Also note that the "standard group" had one drop back in distance, while the gradual group did not and invariably increased their time and distance each week.
It is unfortunate that this study did not have a large enough sample size to measure RRI/1000 hours run, but at least the authors note that. Other authors will take less a small sample size and want a tidal change in the treatment of a condidition such as Achilles tendinopathy and come up with a protocol for treatment that through at least 4 stubborn iterations you are encouraged to continue a painful eccentric exercise program in spite of abject failure.
Steve
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Stephen Pribut, DPM
Clinical Assistant Professor of Surgery
George Washington University School of Medicine
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