Symmetry in Vertical Ground Reaction Force Variables in Distance Runners

Abstract

It has been suggested that the high incidence of injuries in runners may be due to asymmetries of the lower extremities. These asymmetries may lead to differences in vertical ground reaction forces (VGRF) imposed on each side of the body, thus increasing the risk of injury to the limbs. PURPOSE: To compare VGRF variables of the dominant (D) and non-dominant (ND) legs in distance runners. METHODS: Seven distance runners (5 men, 2 women, Mean ± SD: age 30.3 ± 8.0 yr; mass 77.1 ± 10.8 kg; height 1.73 ± 0.10 m)ran over a force platform at a velocity of 4.48 ± 0.04 m/s (mean ± SD). Velocity was measured using a radar gun at the instant when foot contact was made with the platform. Ground reaction force data from five successful foot contacts were collected for each leg and the average values were used for analysis. Force data were normalized to body weight (BW). Five VGRF variables were identified from the data of each side of the body. These variables were impact peak force (F1), time to impact peak force (t1), propulsive peak force (F2), time to propulsive peak force (t2) and impulse (I). Variables of the D and ND sides of the body were compared using paired sample t-tests. A symmetrical index (SI) was calculated for each variable to indicate the percentage difference between the variable measured on the D and ND sides. RESUITS: The SI ranged from 2.7% to 15.6%. There were no significant differences (P > 0.05) in all VGRF variables between the D and ND sides (Table 1).Table 1: Ground reaction force variables and symmetrical index (mean ± SD) in seven distance runners.CONCLUSION: Distance runners may not display bilateral asymmetries in VGRF variables. Further research is needed to determine if differences exist in the medio-lateral and antero-posterior directions.