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Fig. 3. Frequency and phase of wall reaction forces during climbing. (A) Stride frequency increased with increasing average fore-aft velocity (blue circles). Inset: the relationship of stride frequency with speed was similar to the relation found in level ground running (black circles). Level data taken from Full and Tu (Full and Tu, 1990). (B) Power spectra of integrated forces (arbitrary units) while the animal was on the plate averaged over trials from different individuals. Fore-aft and normal forces oscillated at step frequency (average step frequency f_step=17.7±3.7 Hz) while lateral force oscillated at half stepping frequency (f_stance=7.8±1.9 Hz), the stride frequency. (C) Integrated forces from all legs during a single constant average velocity stride (two steps) in fore-aft (blue), lateral (green) and normal (red) direction. The data are normalized to the stride period. Error bars on plot represent ± 1 s.e.m. Standard deviations are approximately four times in magnitude (see Results section for a discussion). Black broken line represents average body weight (N=7 individuals). The stepping pattern for a single representative trial is shown below. The schematics of the cockroach indicate the approximate leg configurations at mid-stance. Legs colored black indicate feet that are in contact with the wall.

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