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Are Initial Contact Conditions Related to Tibial Stress Fracture in Distance Runners?: 110710:15 AM – 10:30 AM

Milner, Clare E.; Davis, Irene S. FACSM; Hamill, Joseph FACSM

Medicine & Science in Sports & Exercise: May 2006 - Volume 38 - Issue 5 - p S123
Presidential Closing Remarks 12:05 PM – 12:15 PM: Immediately Following President's Lectures ROOM: Ballroom 2/3 and Ballroom 1: G-39 Free Communication/Slide – Running Mechanics: SATURDAY, JUNE 3, 2006 9:00 AM – 11:00 AM ROOM: 401

1University of Tennessee, Knoxville, TN.

2University of Delaware, Newark, DE.

3University of Massachusetts, Amherst, MA


Runners with previous tibial stress fracture (TSF) have higher peak tibial shock (TSHK) and vertical loading rates than runners with no bony injuries. These events occur just after foot strike, before the body can respond to surface conditions. Therefore, different initial lower extremity compliance and leg angle may lead to differences in shock and loading rates which might be important in relation to TSF.

PURPOSE: To determine whether runners with previous TSF contact the ground with a stiffer lower extremity. That is, with a more flexed knee (KFLEX) and a more vertical leg (ALEG) at foot contact, plus a stiff er knee (KSTIF) and less flexion excursion (KEXC) from foot strike to impact peak than runners with no injury. A further purpose is to determine whether these variables are correlated with TSHK.

METHODS: Healthy runners who had sustained a TSF previously (RTSF; n = 20) and an age and mileage matched control group with no previous lower extremity bony injury (CTRL; n = 20) provided informed consent and participated. Gait data were collected at 120 Hz (960 Hz analog) as subjects ran at 3.7m/s on a 25m runway. Data from five trials were averaged for analysis. Independent t-tests and effect size (ES) were used to investigate the hypothesized differences between the groups. Pearson Product Moment correlations were used to determine whether initial contact variables were related to TSHK.

RESUITS: (Angles in degrees, stiffness is change in normalized joint moment (Nm/ (mass in kg x height in m)) divided by change in joint angle)



Runners with previous TSF (and, therefore, higher TSHK) have higher KSTIF at initial contact than controls. Furthermore, KSTIF was moderately correlated with TSHK across the sample. Small effects with moderate correlations for KEXC and ALEG suggest that pose of the leg during initial contact is less important.

CONCLUSION: Knee stiffness is greater in runners with previous TSF, but the pose of the leg is not statistically different from controls. Prospective studies are needed to determine whether KSTIF is high prior to TSF.

© 2006 American College of Sports Medicine