BackgroundThe ostrich is a cursorial bird with extraordinary speed and endurance, especially in the desert, and thus is an ideal large-scale animal model for mechanic study of locomotion on granular substrate.MethodsThe plantar pressure distributions of ostriches walking/running on loose sand/solid ground were recorded using a dynamic pressure plate.ResultsThe center of pressure (COP) on loose sand mostly originated from the middle of the 3rd toe, which differed from the J-shaped COP trajectory on solid ground. At mid-stance, a high-pressure region was observed in the middle of the 3rd toe on loose sand, but three high-pressure regions were found on solid ground. The gait mode significantly affected the peak pressures of the 3rd and 4th toes (p = 1.5 × 10−6 and 2.39 × 10−8, respectively), but not that of the claw (p = 0.041). The effects of substrate were similar to those of the gait mode.DiscussionGround reaction force trials of each functional part showed the 3rd toe bore more body loads and the 4th toe undertook less loads. The pressure distributions suggest balance maintenance on loose sand was provided by the 3rd and 4th toes and the angle between their length axes. On loose sand, the middle of the 3rd toe was the first to touch the sand with a smaller attack angle to maximize the ground reaction force, but on solid ground, the lateral part was the first to touch the ground to minimize the transient loading. At push-off, the ostrich used solidification properties of granular sand under the compression of the 3rd toe to generate sufficient traction.

Flexor tendons function as energy storage and shock absorption structures in the tarsometatarso-phalangeal joint (TMTPJ) of ostrich feet during high-speed and heavy-load locomotion. In this study, mechanisms underlying the energy storage and shock absorption of three flexor tendons of the third toe were studied using histology and scanning electron microscopy (SEM). Macroscopic and microscopic structures of the flexor tendons in different positions of TMTPJ were analyzed. Histological slices showed collagen fiber bundles of all flexor tendons in the middle TMTPJ were arranged in a linear-type, but in the proximal and distal TMTPJ, a wavy-type arrangement was found in the tendon of the M. flexor digitorum longus and tendon of the M. flexor perforans et perforatus digiti III, while no regular-type was found in the tendon of the M. flexor perforatus digiti III. SEM showed that the collagen fiber bundles of flexor tendons were arranged in a hierarchically staggered way (horizontally linear-type and vertically linear-type). Linear-type and wavy-type both existed in the proximal TMTPJ for the collagen fiber bundles of the tendon of the M. flexor perforatus digiti III, but only the linear-type was found in the distal TMTPJ. A number of fibrils were distributed among the collagen fiber bundles, which were likely effective in connection, force transmission and other functions. The morphology and arrangement of collagen fiber bundles were closely related to the tendon functions. We present interpretations of the biological functions in different positions and types of the tendons in the TMTPJ of the ostrich feet.

In ostriches, the toes are the only body parts that contact loose sand surfaces. Thus, toe interphalangeal joint motions may play vital biomechanical roles. However, there is little research on ostrich phalangeal joint movements while walking or running on sand. The results from the three-dimensional motion track analysis system Simi Motion show that gait pattern has no significant effect on the key indicators (angles at touch-down, mid-stance, lift-off and range of motion) of the toe joint angles. The motion of the toe phalanges when walking and running on sand is basically the same. The ground medium is the key factor that changes the toe postures adopted by ostriches during the stance phase in slow to fast locomotion. The 3rd toe and the 4th toe are connected by the interphalangeal ligament, and the motions of the MTP3 and MTP4 joints are highly synchronized on a loose sand substrate. The 3rd toe and 4th toe are coupled to maintain static balance in slow locomotion and dynamic balance in fast locomotion. In addition, the gait pattern has a marked effect on the range of forward displacement of the toenail (YTN). The ostrich toenail plays an important role in preventing slip and provides traction at push-off in a sandy environment. The metatarsophalangeal joint plays an important role in energy saving during fast locomotion on loose sand substrates. Simulation reveals that the particle velocity field, particle force field and sand particle disturbance in the running gait are denser than those in the walking gait.

The ostrich is a highly cursorial bipedal land animal with a permanently elevated metatarsophalangeal joint supported by only two toes. Although locomotor kinematics in walking and running ostriches have been examined, these studies have been largely limited to above the metatarsophalangeal joint. In this study, kinematic data of all major toe joints were collected from gaits with double support (slow walking) to running during stance period in a semi-natural setup with two selected cooperative ostriches. Statistical analyses were conducted to investigate the effect of locomotor gait on toe joint kinematics. The MTP3 and MTP4 joints exhibit the largest range of motion whereas the first phalangeal joint of the 4th toe shows the largest motion variability. The interphalangeal joints of the 3rd and 4th toes present very similar motion patterns over stance phases of slow walking and running. However, the motion patterns of the MTP3 and MTP4 joints and the vertical displacement of the metatarsophalangeal joint are significantly different during running and slow walking. Because of the biomechanical requirements, osctriches are likely to select the inverted pendulum gait at low speeds and the bouncing gait at high speeds to improve movement performance and energy economy. Interestingly, the motions of the MTP3 and MTP4 joints are highly synchronized from slow to fast locomotion. This strongly suggests that the 3rd and 4th toes really work as an “integrated system” with the 3rd toe as the main load bearing element whilst the 4th toe as the complementary load sharing element with a primary role to ensure the lateral stability of the permanently elevated metatarsophalangeal joint.

The ostrich is a highly cursorial bipedal land animal with a permanently elevated metatarsophalangeal joint supported by only two toes. Although locomotor kinematics in walking and running ostriches have been examined, these studies have been largely limited to above the metatarsophalangeal joint. In this study, kinematic data of all major toe joints were collected from walking to running during stance period in a semi-natural setup with selected cooperative ostriches. Statistical analyses were conducted to investigate the effect of locomotor gait on toe joint kinematics. The MTP3 and MTP4 joints exhibit the largest range of motion whereas the first phalangeal joint of the 4th toe shows the largest motion variability. The interphalangeal joints of the 3rd and 4th toes present very similar motion patterns over stance phases of walking and running. However, the motion patterns of the MTP3 and MTP4 joints and the vertical displacement of the metatarsophalangeal joint are significantly different during running from walking. This is probably because of the biomechanical requirements for the inverted pendulum gait at low speeds and also the bouncing gait at high speeds. Interestingly, the motions of the MTP3 and MTP4 joints are highly synchronised from slow to fast locomotion. This strongly suggests that the 3rd and 4th toes really work as an integrated system with the 3rd toe as the main load bearing element whilst the 4th toe as the complementary load sharing element with a primary role to ensure the lateral stability of the permanently elevated metatarsophalangeal joint.