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How to assess running kinematics without a fancy 3D motion lab.
In any given year, nearly 80% of runners will report a running-related injury (RRI). Hip weakness and faulty kinematics are frequently implicated in injuries such as iliotibial band syndrome and medial tibial stress syndrome. However, without a high-tech running lab, clinicians have few resources to analyze running form. Therefore, a group of researchers from Montana State University wondered if a common clinical measure might give insight into running kinematics.
The researchers wanted to know if the kinematics observed in a single-leg step down (SLSD) correlated with a subject’s running kinematics. Also, did those runners who demonstrated total medial collapse (a sum of frontal plane motion of the hip, knee, and ankle) when performing the SLSD also exhibit kinetic variables associated with running injuries? Lastly, they were curious about the role that hip abduction and external rotation strength played in the relationship between SLSD and running kinematics.
The study enrolled 50 healthy experienced runners (25 males and 25 females) who ran at least 20 miles per week. They measured hip abductor and external rotator strength using a dynamometer. The researchers captured whole-body kinematics using a 10 camera motion-capture system. They recorded subjects while running over a 20m runway at an easy pace over three force plates and while stepping down from a 15cm box. Ten trials were recorded on each limb while both running and performing the SLSD. The volunteers wore their own shoes throughout the study.
Results and Implications
The kinematics measured during the SLSD were hip adduction, hip internal rotation, knee valgus, and rearfoot eversion. The study found that these measures predicted the running kinematics observed in the male participants. In the female subjects, hip internal rotation, knee valgus, and rearfoot eversion in the SLSD predicted running kinematics. When added together to get a single measurement of movement in the frontal plane, the total media collapse sum did not predict kinetic variables in men. However, it did predict kinetics in the female runners.
Interestingly, when normalized to Nm/kg of body weight, the male and female subjects did not differ significantly in hip abductor and external rotator strength. Furthermore, strength in these areas did not correspond with performance on the SLSD or while running. Therefore, only the SLSD had predictive value in assessing running kinematics.
The authors point out several limitations to this study. The first is that the height of the step may have influenced kinematics. As several studies differ on the step height, they suggest aligning your clinical practice to one of the studies based on your available equipment. For instance, if you can adjust the step based on patient height, then seek out the study that used that method. This study’s step was fixed at 15cm.
That there wasn’t a significant difference in strength between the genders is likely because all the participants were healthy and active runners. In addition, the narrow range of strength among subjects may have hidden any effect of strength upon kinematics. Researchers did not measure the other possible influencing factors in runners such as motor learning, muscle activation, joint mobility, dynamic balance, or flexibility.
In addition, all participants were healthy volunteers. Furthermore, the study used 3D motion capture, while most clinicians only have access to 2D video analysis. While both methods demonstrate interrater reliability and concurrent validity, the authors caution inferring that the study’s results would have been the same with a 2D method.
In this study, the runners ran before performing the SLSD. While the amount of testing during running wasn’t substantial, fatigue must be considered as a possible confounder of results. The runners also self-selected their running speeds during the trials, and they all wore their own shoes.
As this study alludes to the predictive value of the SLSD in healthy runners, this test could be a useful screening tool for pre-season running clinics. Exactly how predictive of injury is SLSD performance remains to be explored. Further research is needed to determine what factors, besides strength, contribute to that performance and their relationship to running kinematics.