USE OF 2-DIMENSIONAL SAGITTAL KINEMATIC VARIABLES TO ESTIMATE GROUND REACTION FORCE DURING RUNNING.

BACKGROUND: Variations in vertical loading rates have been associated with overuse injuries of the lower extremity; however, they are typically collected using 3-dimensional motion capture systems and in-ground force plates not available to most clinicians because of cost and space constraints. PURPOSE: The purpose of this study was to determine if kinetic measures commonly used to describe lower extremity loading characteristics could be estimated from step rate and specific sagittal plane kinematic variables captured using 2-dimensional motion analysis during treadmill running. STUDY DESIGN: Observational Study. METHODS: Ten high school cross-country runners (4 men and 6 women) voluntarily consented to participate in this study. Reflective markers were placed on each lower extremity over multiple anatomical landmarks. Participants were then asked to run on the instrumented treadmill at their preferred running speed. When the participants indicated they were in their typical running pattern, they continued to run at their preferred speed for a minimum of five minutes. After three minutes of running at their preferred running speed, the participant's step rate was counted and after running for four minutes, video and ground reaction force data were recorded for 60 sec. All running motion data were recorded using a single high-speed camera at 240 frames per second and ground reaction force data were sampled at 1000 Hz. RESULTS: Mean kinematic values between the left and right extremities for all 10 participants were not significantly different. Consequently, data for the left and right extremities were grouped for all further analyses. The stepwise forward regression to predict vertical ground reaction force resulted in a five-variable model (step rate and four kinematic variables) with R2 = 0.56. The stepwise forward regression to predict average loading rate also resulted in a five kinematic variable model with R2 = 0.51. CONCLUSIONS: Step rate and sagittal plane kinematic variables measured using a simplified 2-dimensional motion analysis approach with a single high-speed camera can provide the clinician with a reasonable estimate of ground reaction force kinetics during treadmill running. LEVEL OF EVIDENCE: 4, Controlled laboratory study.

Does foot placement affect the reliability of static foot posture measurements?

BACKGROUND: Previous studies have reported conflicting results on whether different foot placements in standing can affect static measurements of foot posture. We sought to determine whether three measurements of static foot posture could be consistently measured in three different foot placements while standing. METHODS: Twenty individuals, 12 women and eight men, with a mean age of 24.8 years consented to participate. Two raters assessed the dorsal arch height, midfoot width, and heel width of each foot while the participant stood in the following three foot placements: a standardized placement, a participant-determined placement after marching in place, and a rater-determined foot placement based on observation of the participant's angle of gait and base of support while walking. RESULTS: All three measurements of static foot posture were shown to have high levels of intrarater and interrater reliability. Significant differences in the measurements of dorsal arch height, midfoot width, and heel width were found among all three of the foot placements. There were no differences between the two raters for any of the three measurements of foot posture. CONCLUSIONS: Based on these findings, we recommend that clinicians perform measurements of static foot posture using the same standing foot placement between sessions to ensure a high level of measurement consistency.

The amount of rearfoot motion used during the stance phase of walking.

The purpose of this study was to determine the proportion of available passive frontal plane rearfoot motion that is used during the stance phase of walking. Data were collected from 40 healthy, asymptomatic volunteer subjects (20 men and 20 women) aged 23 to 44 years. Passive inversion and eversion motion was measured in a non-weightbearing position by manually moving the calcaneus. Dynamic rearfoot motion was referenced to a vertical calcaneus and tibia and was measured using a three-dimensional electromagnetic motion-analysis system. The results indicated that individuals used 68.1% of their available passive eversion range of motion and 13.2% of their available passive inversion range of motion during walking. The clinical implication of individuals' regularly operating at or near the end point of their available rearfoot eversion range of motion is discussed.