Fig. 8. Inclined walking in aged animals. (A) Animals were placed in a treadmill with an acetate belt that was tilted at a 45° angle. The analysis was started when the caudal end of the animal reached the beginning of the incline (START). (B) Trials were recorded as successful when the animal walked up the incline approximately one body length from the START point (END). (C) Leg slipping, defined as a change in the position of the foot on the substrate during the stance phase, was often present during inclined walking in aged animals. The probability of slipping was calculated as the number of slips per step for each animal. Probabilities for each individual were averaged across the population. There were no differences in the amount of leg slipping between animals with and without `tarsus catch'. However, prothoracic legs slipped more often than the mesothoracic or metathoracic legs. (D) Data from the inclined walking trials were reorganized into successful and unsuccessful trials. Significantly more leg slipping in the middle legs was present in failing trials than in successful trials (^*P<0.05). (E) Gait pattern in an aged individual that successfully climbed the incline. Although the front legs often took multiple steps during inclined walking, these animals used a metachronal gait to surmount the incline. (F) Gait pattern in an aged individual that did not successfully climb the incline. Leg movements were not coordinated in this trial and leg slipping was extensive.

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