Evaluation of Lower Extremity Overuse Injury Potential in Runners
ABSTRACT & COMMENTARY
Synopsis: Low-impact forces, a rapid rate of pronation, and greater hamstring flexibility may be related to a reduced risk of overuse injury in runners.
Source: Hreljac A, et al. Evaluation of lower extremity overuse injury potential in runners. Med Sci Sports Exerc 2000;32(9):1635-1641.
This paper compared several anatomical features and biomechanical stride characteristics between runners with history of lower extremity injury and a matched group of runners free from history of injury. Two groups of 20 runners (8 female and 12 male in each) provided data pertaining to training distance, intensity, running surface, shoes worn, changes in training, and stretching habits. The injured group had sustained an overuse injury below the knee but subjects were pain-free at the time of the study and had returned to training for at least three months. Specific diagnoses were not obtained for the injured group. The anatomical data collected included height, weight, longitudinal arch height, footprint index, and hamstring and ankle flexibility. The biomechanical variables included contact time, vertical force impact peak, maximal vertical loading rate, maximum active force peak, maximum push-off force, Achilles tendon angle at touchdown, maximal angle of pronation, total change in Achilles tendon angle, and maximal pronation velocity.
No significant differences were found between groups in average running pace, weekly distance, or any of the other training variables. The statistical analysis for the anatomical and biomechanical data compared the average of right and left side values between groups. The only anatomical difference found between the groups was in flexibility as measured with the sit and reach test. The injured subjects were approximately 6.5° less flexible than the uninjured subjects. The only biomechanical variables that were different between groups were the vertical force impact peak and the maximal vertical loading rate. Hreljac and associates noted a trend toward more rapid pronation and greater touchdown supination.
Comment by David H. Perrin, PhD, ATC
Hreljac et al should be applauded for examining the anatomical and biomechanical factors that may lead to lower extremity injury in runners. Only with this knowledge can clinicians implement preventive strategies founded on experimental rather than anecdotal evidence. Little scientific evidence exists that decreased flexibility leads to an increased rate of injury in runners. Many have speculated that this relationship does exist, and the findings of this study would seem to lend credence to this speculation. It is interesting to note that the injured and uninjured subjects reported no differences in stretching habits. One might speculate that perhaps the differences in flexibility were a result of problems with technique, rather than frequency or duration of stretching.
The primary biomechanical differences between the two groups were excessive impact forces and rates of loading, which were greater in the injured than uninjured group. It seems logical that repeated excessive loading could lead to lower extremity injury. The trend toward more rapid pronation in the uninjured group is also interesting. Pronation is thought by many to be a protective mechanism during running, assuming it is not excessive.
The limitations of the study include the small sample size, and the absence of specific diagnoses of injury. Although a statistical power analysis was not reported, the failure to find statistically significant differences in maximal pronation velocity between the two groups might be due to the sample size. Further research should examine the potential risk factors for injury in runners with larger numbers of subjects and with prospective research designs. Specific injury diagnosis would also enable determination of a cause and effect relationship between anatomical and biomechanical characteristics and type of lower extremity overuse injury.