MOTOR PATTERNS FOR HORIZONTAL AND UPSIDE-DOWN WALKING AND VERTICAL CLIMBING IN THE LOCUST

The motor patterns of the locust's flexor tibiae and metathoracic subc oxal joint muscles were compared during unrestrained horizontal walkin g, vertical climbing and walking upside-down hanging from a branch, Co mbining anatomical and structural data with the results from myographi c recordings revealed the role of these muscles during walking and the ir functional adjustments to different loads and gravity effects cause d by changes in walking conditions, Motor patterns are remarkably cons tant during a given walking situation even at quite different walking speeds, In all walking situations, changes in step duration correlate strongly with changes in the duration of retraction but only weakly wi th the duration of protraction, Different motor units of one muscle ca n be distinguished by their spike amplitude, They may be active simult aneously or they may alternate and then fire in different phases of th e step cycle, For example, during horizontal walking, the small unit o f the first abductor (M125) is active during protraction and the large one during retraction, During retraction, the coral muscles serve two functions: (1) the joint has to be brought back to the posterior extr eme position by retractor muscles; (2) the joint has to be stabilized, that is held 'stiffly', by co-activity of functional antagonists, Dur ing protraction, it is moved to the anterior extreme position by power ful contractions of protractor muscles, The muscular activity patterns show marked differences depending on the walking situation, Some larg e motor units spike only sporadically during horizontal walking but bu rst during vertical climbing and upside-down walking (muscle M121p, th e large units of muscles M126 and M120). During upside-down walking, m uscles M120 and M121 and the large unit of muscle M125 are active duri ng opposite phases of the step cycle when compared with horizontal wal king and vertical climbing (for example, during walking and climbing, muscle M120 is active at the transition between retraction and protrac tion, whereas during upside-down walking, activity occurs during late protraction and early retraction). The results describe how motor patt erns are adjusted to the different requirements of various walking sit uations.