At the other end of the spectrum from sleek, fast-running cockroaches such as P. americana are the muscular, shorter-legged species that burrow into soil or wood. Their legs are usually ornamented with sturdy spines, particularly at the distal end of the tibiae; these function to brace the insect against the sides of the burrow, providing a stable platform for the transmission of force. Fossorial cockroaches are built for power, not speed. When forced to jog on a treadmill, all tested cockroach species exhibited a classic aerobic response to running; oxygen consumption (VO2) rapidly rose to a steady state that persisted for the duration of the workout. When exercise was terminated, the recovery time of P. americana and Blab. discoidalis rivaled or exceeded the performance of the best vertebrate runners (Fig. 2.4). Among the slowest to recover was the heavy-bodied G. portentosa, which took 15-45 min, depending on the speed of the run (Herreid et al., 1981; Herreid and Full, 1984). Some individuals of G. portentosa exhibited obvious signs of fatigue.
They stopped, carried their body closer to the substrate, and had a hard time catching their breath: respiratory movements were exaggerated and the insects maintained their spiracles in a wide-open position.
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