AXIAL KINEMATICS AND MUSCLE-ACTIVITY DURING TERRESTRIAL LOCOMOTION OFTHE CENTIPEDE SCOLOPENDRA-HEROS

For centipedes moving steadily on a treadmill at speeds of 0.5, 1.0 an d 1.5 L s(-1), where L is body length, we obtained video tapes of move ment that were synchronized with electromyograms (EMGs) from lateral f lexor muscles at six standardized longitudinal positions, Field-by-hel d analysis of video tapes revealed posteriorly propagated waves of ben ding at all speeds, Muscle activity was also propagated posteriorly at the same speed as the kinematic wave, and EMGs of the lateral flexors were generally unilateral and alternating (between the left and right sides), The timing of EMG activity relative to lateral bending was co nsistent with electrical activity during the shortening of muscle fibe rs; therefore, activity of the axial musculature appears to cause late ral bending, Analysis of variance revealed widespread effects of speed on both kinematic and electromyographic variables, whereas longitudin al position within the centipede (between body segments 8 and 18) gene rally did not have significant effects on the same variables, For exam ple, as speed increased from 0.5 to 1.5 L s(-1), the amplitude of late ral displacement approximately doubled and the amplitude of lateral be nding increased approximately threefold, Lag times (in seconds) indica ting the propagation of kinematic and EMG events along the length of t he centipede decreased significantly with speed, Phase lags among long itudinal sites decreased significantly with increased speed, indicatin g that the kinematic and EMG wavelengths increased with increased spee d, EMG duration approximated 50% of cycle duration and was unaffected by speed, and the phase of the EMG activity relative to lateral bendin g was also unaffected by locomotor speed. Hence, all results from all speeds are consistent with active bending of the axial segments during centipede locomotion, conflicting with the widely accepted hypothesis that lateral bending is imposed on the body by the metachronal steppi ng pattern of the legs and that bending is resisted by axial muscles.