GROUND REACTION FORCES AND SPATIO-TEMPORAL VARIABLES DURING BAREFOOT AND SHOD RUNNING
AbstractINTRODUCTION The purpose of this study was to investigate the variations in step length, step frequency and ground reaction forces between barefoot and shod-foot running at three different velocities. Nine trained, male runners (age : 27.3 k 9 years ; height : 1.78 ? 0.07 m ; weight : 70 i 9 kg) were tested by using a Kistler force plate and by film analysis while running on a. 40m indoor runway. Ten trials, both barefoot and shod, at 3 different speeds (3.5, 4.5 and 5.5 m.sel) were analyzed with two-factor Anova tests with repeated measures with a significance level p r 0.05. The variables characterizing the vertical ground reaction forces (right foot) were defined following Nigg (1 986). RESULTS AND CONCLUSION All variables change significantly with Increasing speed. The increase of step length and step frequency support the findings in previous studies (Komi ef a/, 1987; Cavanagh and Kram, 1990). For the barefoot and shod-foot condition, there is a significant difference for all variables except for the amplitude of the Impact and active peak (Fzi and Fza). Considering the vertical ground reaction forces, more than one impact peak was seen during barefoot running. Although the amplitude of the impact peaks does not differ significantly, the maximal loading rate (Gzi = Fzilti) which is an important variable determining the impact load during heelstrike, is significantly larger in the barefoot condition. This supports the thesis that in barefoot running a maxmal deformation of the fatty heel tissue reduces its shock reduction capacity at heelstrike (De Clercq et a/, 1994). During push-off no important differences were found. A larger step frequency and a smaller step length for the barefoot condition were found. One possible explanation could be that the runners adapt a strategy to decrease the local stress underneath the heel (= pain sensation) in the barefoot condition. Taking smaller steps will change the touchdown conditions, with a larger plantar flexion of the bare foot as result. But further investigation of other kinematic variables of these nine persons will explain more clearly the differences found till now. REFERENCES Cavanagh, P.R. & Kram, R. (1990) in Cavanagh (Ed.) Biomechanics of distance running, Champaign, IL De Clercq, D. et al (1994). J. Biomechanics, 27(1 O), 121 3-1222. Komi, P.V. et al (1987). Int. J. Sports Med, 8, 196-202. Nigg, B.M. (1986). Biomechanics of running shoes, Champaign.IL.
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