A COMPARISON OF LOWER EXTREMITY FORCES, JOINT ANGLES, AND MUSCLE ACTIVITY DURING SHOD AND BAREFOOT RUNNING

Abstract

INTRODUCTION: Knowledge of the characteristics of barefoot running may enhance understanding of the muscular and gait modifications induced by wearing shoes. METHOD: Nine male competitive heel strike runners ran naturally across a Kistler force platform, mounted beneath a polyflex track, with the right foot while running at a speed of 4.5ms-1 +7.5%. Joint angular data was determined from marker digitisation of 100 Hz cine filming performed perpendicular to the plane of motion. Radiotelemetry was used to record the activity of six leg muscles: vastus medialis (VM); vastus lateralis (VL); rectus femoris (RF); tibialis anterior (TA); medial gastrocnemius (MG); lateral gastrocnemius (LG). Subject characteristics (mean, SD) were: age 30.8 +10.6 years; height 1.77 +0.06m; mass 70.9 +9.0kg. RESULTS: For all subjects the mean respective speeds (mean, SD) of the eight shod and barefoot running were 4.64ms-1 and 4.53ms-1, and these were not significantly different (P>0.05). In barefoot running the mean peak vertical impact force with respect to body weight(BW) was significantly higher, and mean minimal vertical impact lower. Also, the time to peak mean vertical impact, mean peak braking force and the stance time were significantly less in barefoot running. [table] Joint angles were determined at the hip, knee, ankle and knee-ankle-heel angle 10ms prior to impact, at impact, sole of the foot/shoe flat, maximum knee flexion and heel off. Of the twenty comparisons only three were significant, the barefoot ankle angle was significantly lower at heel off (), the barefoot knee-ankleheel angle was significantly lower at maximum knee flexion () and the barefoot knee-ankle-heel angle was significantly lower at heel off (). Analysis of within subject muscle activity indicated that in barefoot running TA activity at impact was less than in shod running, and LG and/or MG activity often increased before impact. Increases in VL,VM, and RF activity were frequently observed during barefoot running. CONCLUSION: Leg muscular activity alterations at impact are generally evident between barefoot and shod running, but there are interindividual differences.