Slopes and speed related effects on kinematic and EMG patterns in elite race walking

Introduction. In human locomotion every external condition generates a strategy. The aim of this study is to analyze the kinematics parameters and to indentify the changes in movement pattern and muscle activity of race-walkers (RW). Methods. Twelve elite RW have race walking on a treadmill for 5 minutes each slope (0, 2 and 7%) in iso-efficiency speed (IES1) with heart rate and sEMG on leg muscles constantly monitored. Digital cameras (210 Hz) were used to record; Dartfish 5.5Pro was used to perform a 2D video analysis, while for statistical analysis was used Anova. (1) The IES (km/h) for each subject at 0% grade was the average speed during the best performance in the 10000 m race, minus 1 km/h, which corresponds to the ~50% Vo2MAX and requires an energy cost (Cw0) of 5.0 J/m/kg according to previous studies (Di Prampero 1986). Moreover, according to previous data (Minetti et al. 2002) the increase of Cw as a function of ground slope is: 0.15 * slope (%) + Cw0. We calculated for each ground slope the IES at which the Vo2 was equal to the oxygen consumption during level race walking using the following equation: Vo2= (Cw0/21(J/m) * (IES0/0.06 (m/min)) IES= (Vo2 * 21 * 0.06)/(0.15(Cw) * slope (%) + (Cw0)) Results IES, step length (SL) and frequency (SF) decrease as a function of the increasing slope: IES0 12.5 – IES2 11.8 – IES7 10.3; SL= (0-2%= -3.71%, n.s.; 0-7%= -12.23%, p<0.001); SF= (0-2%= -2.38%, n.s.; 0-7%= -6.07%, p<0.01). The contact time (CT) and heart rate (HR) increase at the increasing slope: CT= (0-2%= 2.46%, n.s.; 0-7%= 6.56%, p<0.01); HR= (0-2%= 0.62%, n.s.; 0-7%= 3.25%, p<0.05). The sEMG activity was reduced at the increasing slope in: tibialis anterior (0-2%= 22.49%, p<0.0001; 0-7%= 41.18%, p<0.0001); rectus femoris (0-2%= 15.35%, p<0.0001; 0-7%= 29.13%, p<0.0001). While the sEMG activity was increased in this muscles: vastus lateralis (0-2%= 22.95%, p<0.0001; 0-7%= 31.15%, p<0.0001); gastrocnemius medialis (0-2%= 21.40%, p<0.001; 0-7%= 48.37%, p<0.0001); biceps femoris (0-2%= 190.78%, p<0.0001; 0-7%= 201.37%, p<0.0001). Discussion. These results provide the resultant of the real mechanical work in different slopes without increasing energetic cost, validating the equation to calculate the speed in RW only at IES between zero and 2% gradient. While for higher gradient levels the procedure used in this study seems to overestimate the speed, probably due to the different biomechanics between walking (Minetti et al., 2002) and race walking. References Di Prampero PE. The energy cost of human locomotion on land and in water. (1986). Int J Sports Med, 7 (2), 55-72. Minetti AE, Moia C, Roi GS, Susta D, Ferretti G. Energy cost of walking and running at extreme uphill and downhill slopes. (2002). J Appl Physiol, 93(3),1039-1046.