Underground locomotion in moles: kinematic and electromyographic studies of locomotion in the Japanese mole (Mogera wogura)

Abstract

A series of kinematic and electromyographic (EMG) studies were conducted to characterize the neural control of underground movement in the Japanese mole, Mogera wogura. For the purposes of the present study, the locomotion of moles was classified into two modes: crawling, which comprises alternate movements of the left and right forelimbs; and burrowing, in which both forelimbs move synchronously. In crawling, moles exhibit both symmetrical and asymmetrical locomotion independent of cycle duration and speed of travel. In burrowing, the movements of fore- and hindlimbs, and of the left and right hindlimb are loosely coordinated. We divided cycles of limb movement into recovery stroke phase and power stroke phases and observed that control of cycle duration in forelimbs and hindlimbs was achieved through changes to both recovery and power stroke phases. Our results showed phasic EMG bursts in various muscles in moles, whose timing differed from that seen in terrestrial four-legged mammals such as cats and dogs. The difference was especially apparent in the m. longissimus, in which EMG bursts recorded at the level of the thoracic and lumbar vertebrae corresponded to movements of the forelimbs and hindlimbs, respectively. Thus, we conclude that moles have evolved a distinctive mechanism of neural control to perform their specialized forms of underground locomotion.